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Aras M, Güler-Kılıç S, Kılıç Ç. Enhancement of the magnetic anisotropy in single semiconductor nanowires via surface doping and adatom deposition. NANOTECHNOLOGY 2022; 33:205202. [PMID: 35105830 DOI: 10.1088/1361-6528/ac50f0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2021] [Accepted: 02/01/2022] [Indexed: 06/14/2023]
Abstract
The magnetic anisotropy of single semiconductor (ZnO and GaN) nanowires incorporating both a transition metal (Co and Mn, respectively) as a substitutional surface dopant and a heavy metal (Au, Bi, or Pt) adatom is studied by performing density-functional supercell calculations with the HubbardUcorrection. It is found that a substantial enhancement in the magnetic anisotropy energy is obtained through the deposition of Bi; the deposition of Au and Pt leads to significant variation in other magnetic properties, but not in the magnetic anisotropy energy. An analysis within a band description shows that the coexistence of Bi adatom and a surface dopant with large spin moment activates a mechanism involving reorientation and readjustment of the spin moments of electrons in occupied bands in response to the change of magnetization direction, which promotes giant magnetic anisotropy. Our results for adsorption energetics indicate that the accommodation of Bi in the neighborhood of the surface dopant is more likely in GaN nanowires, because the Bi adatom does (not) tend to be closer to the Mn (Co) dopant on the surface of GaN (ZnO) nanowire. The stability of GaN nanowire with giant magnetic anisotropy owing to the incorporation of both Mn and Bi is demonstrated by performingab initiomolecular dynamics simulations at temperatures considerably higher than room temperature. These results suggest that adatom deposition and surface doping can be used complementarily to develop single nanowire-based spintronic devices.
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Affiliation(s)
- Mehmet Aras
- Department of Physics, Gebze Technical University, Gebze, Kocaeli 41400, Turkey
| | - Sümeyra Güler-Kılıç
- Department of Physics, Gebze Technical University, Gebze, Kocaeli 41400, Turkey
| | - Çetin Kılıç
- Department of Physics, Gebze Technical University, Gebze, Kocaeli 41400, Turkey
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2
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Trishin S, Lotze C, Bogdanoff N, von Oppen F, Franke KJ. Moiré Tuning of Spin Excitations: Individual Fe Atoms on MoS_{2}/Au(111). PHYSICAL REVIEW LETTERS 2021; 127:236801. [PMID: 34936798 DOI: 10.1103/physrevlett.127.236801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Accepted: 10/14/2021] [Indexed: 06/14/2023]
Abstract
Magnetic adatoms on properly designed surfaces constitute exquisite systems for addressing, controlling, and manipulating single quantum spins. Here, we show that monolayers of MoS_{2} on a Au(111) surface provide a versatile platform for controllably tuning the coupling between adatom spins and substrate electrons. Even for equivalent adsorption sites with respect to the atomic MoS_{2} lattice, we observe that Fe adatoms exhibit behaviors ranging from pure spin excitations, characteristic of negligible exchange and dominant single-ion anisotropy, to a fully developed Kondo resonance, indicating strong exchange and negligible single-ion anisotropy. This tunability emerges from a moiré structure of MoS_{2} on Au(111) in conjunction with pronounced many-body renormalizations. We also find striking spectral variations in the immediate vicinity of the Fe atoms, which we explain by quantum interference reflecting the formation of Fe-S hybrid states despite the nominally inert nature of the substrate. Our work establishes monolayer MoS_{2} as a tuning layer for adjusting the quantum spin properties over an extraordinarily broad parameter range. The considerable variability can be exploited for quantum spin manipulations.
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Affiliation(s)
- Sergey Trishin
- Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Christian Lotze
- Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Nils Bogdanoff
- Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Felix von Oppen
- Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
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3
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González-García A, López-Pérez W, González-Hernández R, Bacaksiz C, Šabani D, Milošević MV, Peeters FM. Transition-metal adatoms on 2D-GaAs: a route to chiral magnetic 2D materials by design. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:145803. [PMID: 33503605 DOI: 10.1088/1361-648x/abe077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 01/27/2021] [Indexed: 06/12/2023]
Abstract
Using relativistic density-functional calculations, we examine the magneto-crystalline anisotropy and exchange properties of transition-metal atoms adsorbed on 2D-GaAs. We show that single Mn and Mo atom (Co and Os) strongly bind on 2D-GaAs, and induce local out-of-plane (in-plane) magnetic anisotropy. When a pair of TM atoms is adsorbed on 2D-GaAs in a close range from each other, magnetisation properties change (become tunable) with respect to concentrations and ordering of the adatoms. In all cases, we reveal presence of strong Dzyaloshinskii-Moriya interaction. These results indicate novel pathways towards two-dimensional chiral magnetic materials by design, tailored for desired applications in magneto-electronics.
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Affiliation(s)
- A González-García
- Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla, Colombia
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - W López-Pérez
- Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla, Colombia
| | - R González-Hernández
- Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla, Colombia
| | - C Bacaksiz
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Belgium
- Bremen Center for Computational Material Science (BCCMS), Bremen D-28359, Germany
- Computational Science Research Center, Beijing and Computational Science and Applied Research Institute Shenzhen, Shenzhen, People's Republic of China
| | - D Šabani
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Belgium
| | - M V Milošević
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Belgium
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Belgium
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4
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Seifert TS, Kovarik S, Juraschek DM, Spaldin NA, Gambardella P, Stepanow S. Longitudinal and transverse electron paramagnetic resonance in a scanning tunneling microscope. SCIENCE ADVANCES 2020; 6:eabc5511. [PMID: 32998882 PMCID: PMC7527223 DOI: 10.1126/sciadv.abc5511] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Accepted: 08/13/2020] [Indexed: 06/11/2023]
Abstract
Electron paramagnetic resonance (EPR) spectroscopy is widely used to characterize paramagnetic complexes. Recently, EPR combined with scanning tunneling microscopy (STM) achieved single-spin sensitivity with sub-angstrom spatial resolution. The excitation mechanism of EPR in STM, however, is broadly debated, raising concerns about widespread application of this technique. We present an extensive experimental study and modeling of EPR-STM of Fe and hydrogenated Ti atoms on a MgO surface. Our results support a piezoelectric coupling mechanism, in which the EPR species oscillate adiabatically in the inhomogeneous magnetic field of the STM tip. An analysis based on Bloch equations combined with atomic-multiplet calculations identifies different EPR driving forces. Specifically, transverse magnetic field gradients drive the spin-1/2 hydrogenated Ti, whereas longitudinal magnetic field gradients drive the spin-2 Fe. Also, our results highlight the potential of piezoelectric coupling to induce electric dipole moments, thereby broadening the scope of EPR-STM to nonpolar species and nonlinear excitation schemes.
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Affiliation(s)
- Tom S Seifert
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland.
| | - Stepan Kovarik
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| | - Dominik M Juraschek
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
- Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
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5
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Kozanecki M, Rudowicz C. Importance of the fourth-rank zero field splitting parameters for Fe 2+ ( S = 2) adatoms on the CuN/Cu(100) surface evidenced by their determination based on DFT and experimental data. Phys Chem Chem Phys 2020; 22:19837-19844. [DOI: 10.1039/d0cp02986f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Equations allow to determine 2nd- and 4th-rank ZFSPs (Bkq) based on spin energy levels (λi) at B = 0. This method is applied to Fe2+ (S = 2) adatoms on CuN/Cu(100) surface using DFT and experimental data. Relative importance of ZFSPs is analyzed.
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Affiliation(s)
- Michał Kozanecki
- Faculty of Chemistry
- Adam Mickiewicz University
- 61-614 Poznań
- Poland
| | - Czesław Rudowicz
- Faculty of Chemistry
- Adam Mickiewicz University
- 61-614 Poznań
- Poland
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6
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Wang Y, Li X, Yang J. Spin-flip excitations induced by dehydrogenation in a magnetic single-molecule junction. J Chem Phys 2019; 151:224704. [DOI: 10.1063/1.5129288] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Yu Wang
- Institute for Advanced Study, Shenzhen University, Shenzhen 518060, China
| | - Xiaoguang Li
- Institute for Advanced Study, Shenzhen University, Shenzhen 518060, China
| | - Jinlong Yang
- Hefei National Laboratory for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
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7
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Brahimi S, Bouzar H, Lounis S. Impact of single atomic defects and vacancies on the magnetic anisotropy energy of CoPt thin films. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:435803. [PMID: 31284270 DOI: 10.1088/1361-648x/ab2ffb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The impact of surface vacancies and single adatoms on the magnetic properties of tetragonal L1 0 CoPt thin films is investigated from first principles. We consider Co and Fe single adatoms deposited on a Pt-terminated thin film while a Pt adatom is assumed to be supported by a Co-terminated film. The vacancy is injected in the top-surface layer of the films with both types of termination. After finding the most stable location of the defects, we discuss their magnetic properties tied to those of the substrate and investigate the magnetocrystalline anisotropy energy (MAE). Previous simulations (Brahimi et al 2016 J. Phys.: Condens. Matter 28 496002) predicted a large out-of-plane surface MAE for the Pt-terminated CoPt films (4 meV per f.u.) in contrast to in-plane surface MAE for Co-terminated films (-1 meV per f.u.). Here, we find that the surface MAE is significantly modified upon the presence of the atomic defects. All investigated defects induce an in-plane MAE, which is large enough for Fe adatom and Pt vacancy to switch the surface MAE from out-of-plane to in-plane for the Pt-terminated films. Interestingly, among the investigated defects Pt vacancy has the largest effect on the MAE in contrast to Co vacancy, which induced the smallest but still significant effect. This behavior is explained in terms of the orbital moment anisotropy of the thin films.
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Affiliation(s)
- Samy Brahimi
- Laboratoire de Physique et Chimie Quantique, Université Mouloud Mammeri de Tizi-Ouzou, 15000 Tizi-Ouzou, Algeria
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Balashov T, Meyer M, Wulfhekel W. A compact ultrahigh vacuum scanning tunneling microscope with dilution refrigeration. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:113707. [PMID: 30501324 DOI: 10.1063/1.5043636] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Accepted: 10/25/2018] [Indexed: 06/09/2023]
Abstract
We have designed and built a scanning tunneling microscope (STM) setup for operation at millikelvin temperatures in an ultrahigh vacuum. A compact cryostat with an integrated dilution refrigerator has been built that allows measurements at a base temperature of 25 mK in the magnetic field up to 7.5 T with low mechanical and electronic noise. The cryostat is not larger than conventional helium bath cryostats (23 and 13 l of nitrogen and helium, respectively) so that the setup does not require a large experimental hall and fits easily into a standard lab space. Mechanical vibrations with running dilution circulation were kept below 1 pm/ Hz by mechanically decoupling the STM from the cryostat and the pumping system. All electronic input lines were low-pass filtered, reducing the electronic temperature to below 100 mK, as deduced from the quasiparticle peaks of superconducting aluminum. The microscope is optically accessible in the parked position, making sample and tip exchange fast and user-friendly. For measurement, the STM is lowered 60 mm down so that the sample ends in the middle of a wet superconducting magnetic coil.
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Affiliation(s)
- T Balashov
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany
| | - M Meyer
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany
| | - W Wulfhekel
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany
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9
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Ibañez-Azpiroz J, Dos Santos Dias M, Blügel S, Lounis S. Spin-fluctuation and spin-relaxation effects of single adatoms from first principles. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:343002. [PMID: 30020083 DOI: 10.1088/1361-648x/aad43d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Single adatoms offer an exceptional playground for studying magnetism and its associated dynamics at the atomic scale. Here we review recent results on single adatoms deposited on metallic substrates, based on time-dependent density functional theory. First we analyze quantum zero-point spin-fluctuations (ZPSF) as calculated from the fluctuation-dissipation theorem, and show how they affect the magnetic stability by modifying the magnetic anisotropy energy. We also assess the impact of ZPSF in the limit of small hybridization to the substrate characteristic of semi-insulating substrates, connecting to recent experimental investigations where magnetic stability of a single adatom was achieved for the first time. Secondly, we inspect further the dynamics of single adatoms by considering the longitudinal and transverse spin-relaxation processes, whose time-scales are analyzed and related to the underlying electronic structure of both the adatom and the substrate. Thirdly, we analyze spin-fluctuation modes of paramagnetic adatoms, i.e. adatoms where the Stoner criterion for magnetism is almost fulfilled. Interestingly, such modes can develop well-defined peaks in the meV range, their main characteristics being determined by two fundamental electronic properties, namely the Stoner parameter and the density of states at the Fermi level. Furthermore, simulated inelastic scanning tunneling spectroscopy curves reveal that these spin-fluctuation modes can be triggered by tunneling electrons, opening up potential applications also for paramagnetic adatoms. Lastly, an overview of the outstanding issues and future directions is given.
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Affiliation(s)
- Julen Ibañez-Azpiroz
- Centro de Física de Materiales, Universidad del País Vasco, 20018 San Sebastián, Spain
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10
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Yuan HK, Cui H, Liu B, Tian CL, Kuang AL, Chen H. Density functional theory calculations for magnetic properties of Co 3W systems. J Chem Phys 2018; 149:014303. [PMID: 29981542 DOI: 10.1063/1.5029398] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Cheaper permanent magnetic nanostructures with magnetic properties equivalent to those of noble-metal or rare-earth nanomagnets have been experimentally developed for their potential applications in ultrahigh storage densities in magnetic memory. To date, their intrinsic magnetic properties are not well understood under the micro-level of local atomic arrangements and electronic structures. In this work, we performed theoretical investigations on the Co3W bulk, the clean surface, nanoclusters, and the Co|Co3W bilayers and superlattices for their geometrical structures, magnetic moments, and magnetic anisotropy energies (MAEs). We found that the Co3W nanostructures we constructed are stable and have the local minima in the energetic landscape, whose stabilities increase with increasing proportion of W and cluster size. The Co and W atoms in clusters are antiferromagnetically coupled, and their local magnetic moments decrease with increasing proportion of W. The breakdown of the Hund's third rule in W atoms observed in experiment can be interpreted as the competition between the intra-atomic spin-orbit coupling in W atoms and interatomic Co-W hybridizations. The highest MAE of about a few tens of meV is obtained in small cluster sizes, whereas it is an order of magnitude reduction in large cluster sizes. The magnetic systems of Co3W clean surface, Co|Co3W bilayer and superlattice can present large MAEs, and their easy-axes of magnetization are perpendicular to the (001) surface. Our calculated MAEs are of the same order of magnitude as that of the experimental measurements, and the electronic origin is revealed through the second-order perturbation method.
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Affiliation(s)
- H K Yuan
- School of Physical Science and Technology, Southwest University, Chongqing 400715, People's Republic of China
| | - H Cui
- School of Mechanical Engineering, Shaanxi University of Technology, Hanzhong, Shaanxi 723001, People's Republic of China
| | - B Liu
- School of Physical Science and Technology, Southwest University, Chongqing 400715, People's Republic of China
| | - C L Tian
- School of Physical Science and Technology, Southwest University, Chongqing 400715, People's Republic of China
| | - A L Kuang
- School of Physical Science and Technology, Southwest University, Chongqing 400715, People's Republic of China
| | - H Chen
- School of Physical Science and Technology, Southwest University, Chongqing 400715, People's Republic of China
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11
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Bar AK, Kalita P, Singh MK, Rajaraman G, Chandrasekhar V. Low-coordinate mononuclear lanthanide complexes as molecular nanomagnets. Coord Chem Rev 2018. [DOI: 10.1016/j.ccr.2018.03.022] [Citation(s) in RCA: 77] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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12
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Hermenau J, Ternes M, Steinbrecher M, Wiesendanger R, Wiebe J. Long Spin-Relaxation Times in a Transition-Metal Atom in Direct Contact to a Metal Substrate. NANO LETTERS 2018; 18:1978-1983. [PMID: 29466854 DOI: 10.1021/acs.nanolett.7b05392] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Long spin-relaxation times are a prerequisite for the use of spins in data storage or nanospintronics technologies. An atomic-scale solid-state realization of such a system is the spin of a transition-metal atom adsorbed on a suitable substrate. For the case of a metallic substrate, which enables the direct addressing of the spin by conduction electrons, the experimentally measured lifetimes reported to date are on the order of only hundreds of femtoseconds. Here, we show that the spin states of iron atoms adsorbed directly on a conductive platinum substrate have a surprisingly long spin-relaxation time in the nanosecond regime, which is comparable to that of a transition metal atom decoupled from the substrate electrons by a thin decoupling layer. The combination of long spin-relaxation times and strong coupling to conduction electrons implies the possibility to use flexible coupling schemes to process the spin information.
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Affiliation(s)
- Jan Hermenau
- Department of Physics , Hamburg University , Jungiusstrasse 11 , D-20355 Hamburg , Germany
| | - Markus Ternes
- Max-Planck Institute for Solid State Research , Heisenbergstrasse 1 , D-70569 Stuttgart , Germany
| | - Manuel Steinbrecher
- Department of Physics , Hamburg University , Jungiusstrasse 11 , D-20355 Hamburg , Germany
| | - Roland Wiesendanger
- Department of Physics , Hamburg University , Jungiusstrasse 11 , D-20355 Hamburg , Germany
| | - Jens Wiebe
- Department of Physics , Hamburg University , Jungiusstrasse 11 , D-20355 Hamburg , Germany
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13
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Huang Z, Zhang Y, He Y, Song H, Yin C, Wu K. A chemist's overview of surface electron spins. Chem Soc Rev 2018; 46:1955-1976. [PMID: 28317957 DOI: 10.1039/c6cs00891g] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
This review summarizes recent research progress in the measurement and tuning of the electron spins of alien atoms and molecules adsorbed on well-defined substrates. After a brief introduction to the main experimental techniques employed to study surface electron spins, some well-explored systems consisting of atomic and molecular spin-carriers at surfaces are overviewed from a chemist's viewpoint, focusing on the experimental measurements and chemical modifications of the electron spin states of the alien entities at the surfaces on the atomic/molecular level. Finally, personal perspectives have been provided, aiming at describing some of the remaining issues that need to be addressed in the future and proposing potential applications in surface chemistry.
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Affiliation(s)
- Zhichao Huang
- BNLMS, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
| | - Yajie Zhang
- BNLMS, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
| | - Yang He
- BNLMS, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
| | - Huanjun Song
- BNLMS, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
| | - Cen Yin
- BNLMS, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
| | - Kai Wu
- BNLMS, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
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14
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Mishra P, Qi ZK, Oka H, Nakamura K, Komeda T. Spatially Resolved Magnetic Anisotropy of Cobalt Nanostructures on the Au(111) Surface. NANO LETTERS 2017; 17:5843-5847. [PMID: 28806089 DOI: 10.1021/acs.nanolett.7b03114] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Understanding the origin of perpendicular magnetic anisotropy in surface-supported nanoclusters is crucial for fundamental research as well as data storage applications. Here, we investigate the perpendicular magnetic anisotropy energy (MAE) of bilayer cobalt islands on Au(111) substrate using spin-polarized scanning tunneling microscopy at 4.6 K and first-principles theoretical calculations. Au(111) substrate serves as an excellent model system to study the effect of nucleation site and stacking sequence on MAE. Our measurements reveal that the MAE of bilayer islands depends strongly on the crystallographic stacking of the two Co layers and nucleation of the third layer. Moreover, the MAE of Co atoms on Au(111) is enhanced by a factor of 1.75 as compared to that reported on Cu(111). Our first-principles calculations attribute this enhancement to the large spin-orbit coupling of the Au atoms. Our results highlight the strong impact of nanometer-scale structural changes in Co islands on MAE and emphasize the importance of spatially resolved measurements for the magnetic characterization of surface-supported nanostructures.
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Affiliation(s)
- Puneet Mishra
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University , Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan
| | - Zhi Kun Qi
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University , Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan
| | - Hirofumi Oka
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University , Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan
| | - Kohji Nakamura
- Department of Physics Engineering, Mie University , Tsu, Mie 514-8507, Japan
| | - Tadahiro Komeda
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University , Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan
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15
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Rudowicz C, Tadyszak K. Single magnetic 3dN adatoms on surfaces – Proper outlook on compatibility of orthorhombic zero-field splitting parameters and their relationships with magnetic anisotropy quantities. Polyhedron 2017. [DOI: 10.1016/j.poly.2017.01.052] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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16
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The geometric phase of Z n- and T-symmetric nanomagnets as a classification toolkit. Sci Rep 2017; 7:46614. [PMID: 28440279 PMCID: PMC5404233 DOI: 10.1038/srep46614] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Accepted: 03/21/2017] [Indexed: 11/08/2022] Open
Abstract
We derive the general form of the non-trivial geometric phase resulting from the unique combination of point group and time reversal symmetries. This phase arises e.g. when a magnetic adatom is adsorbed on a non-magnetic Cn crystal surface, where n denotes the fold of the principal axis. The energetic ordering and the relevant quantum numbers of the eigenstates are entirely determined by this quantity. Moreover, this phase allows to conveniently predict the protection mechanism of any prepared state, shedding light onto a large number of experiments and allowing a classification scheme. Owing to its robustness this geometric phase also has great relevance for a large number of applications in quantum computing, where topologically protected states bearing long relaxation times are highly desired.
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17
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Zhang KC, Li YF, Liu Y, Zhu Y, Shi LB. Giant magnetic anisotropy of rare-earth adatoms and dimers adsorbed by graphene oxide. Phys Chem Chem Phys 2017; 19:13245-13251. [DOI: 10.1039/c7cp01641g] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The rare-earth dimers adsorbed onto graphene oxide possess huge magnetic anisotropy which can be effectively tuned by electric field.
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Affiliation(s)
- Kai-Cheng Zhang
- College of Mathematics and Physics
- Bohai University
- Jinzhou 121013
- China
| | - Yong-Feng Li
- School of Science
- Inner Mongolia University of Science and Technology
- Baotou 014010
- China
- Key laboratory of Integrated Exploitation of Bayan Obo Multi-Metal Resources
| | - Yong Liu
- State Key Laboratory of Metastable Materials Science & Technology and College of Science
- Yanshan University
- Qinhuangdao 066004
- China
| | - Yan Zhu
- Department of Physics
- Nanjing University of Aeronautics and Astronautics
- Nanjing 210016
- China
| | - Li-Bin Shi
- College of Mathematics and Physics
- Bohai University
- Jinzhou 121013
- China
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18
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Akin ST, Zamudio-Bayer V, Duanmu K, Leistner G, Hirsch K, Bülow C, Ławicki A, Terasaki A, Issendorff BV, Truhlar DG, Lau JT, Duncan MA. Size-Dependent Ligand Quenching of Ferromagnetism in Co 3(benzene) n+ Clusters Studied with X-ray Magnetic Circular Dichroism Spectroscopy. J Phys Chem Lett 2016; 7:4568-4575. [PMID: 27779876 DOI: 10.1021/acs.jpclett.6b01839] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Cobalt-benzene cluster ions of the form Co3(bz)n+ (n = 0-3) were produced in the gas phase, mass-selected, and cooled in a cryogenic ion trap held at 3-4 K. To explore ligand effects on cluster magnetic moments, these species were investigated with X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopy. XMCD spectra yield both the spin and orbital angular momenta of these clusters. Co3+ has a spin magnetic moment of μS = 6 μB and an orbital magnetic moment of μL = 3 μB. Co3(bz)+ and Co3(bz)2+ complexes were found to have spin and orbital magnetic moments identical to the values for ligand-free Co3+. However, coordination of the third benzene to form Co3(bz)3+ completely quenches the high spin state of the system. Density functional theory calculations elucidate the spin states of the Co3(bz)n+ species as a function of the number of attached benzene ligands, explaining the transition from septet to singlet for n = 0 → 3.
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Affiliation(s)
- Scott T Akin
- Department of Chemistry, University of Georgia , Athens, Georgia 30602, United States
| | - Vicente Zamudio-Bayer
- Institut für Methoden und Instrumentierung der Forschung mit Synchrotronstrahlung, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
- Physikalisches Institut, Universität Freiburg , Stefan-Meier-Straße 21, 79104 Freiburg, Germany
| | - Kaining Duanmu
- Department of Chemistry, Chemical Theory Center, and the Supercomputing Institute, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Georg Leistner
- Institut für Methoden und Instrumentierung der Forschung mit Synchrotronstrahlung, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
- Institut für Optik und Atomare Physik, Technische Universität Berlin , Hardenbergstraße 36, 10623 Berlin, Germany
| | - Konstantin Hirsch
- Institut für Methoden und Instrumentierung der Forschung mit Synchrotronstrahlung, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
- Institut für Optik und Atomare Physik, Technische Universität Berlin , Hardenbergstraße 36, 10623 Berlin, Germany
| | - Christine Bülow
- Institut für Methoden und Instrumentierung der Forschung mit Synchrotronstrahlung, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
- Institut für Optik und Atomare Physik, Technische Universität Berlin , Hardenbergstraße 36, 10623 Berlin, Germany
| | - Arkadiusz Ławicki
- Institut für Methoden und Instrumentierung der Forschung mit Synchrotronstrahlung, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
| | - Akira Terasaki
- East Tokyo Laboratory, Genesis Research Institute, Inc. , 717-86 Futamata, Ichikawa, Chiba 272-0001, Japan
- Department of Chemistry, Faculty of Science, Kyushu University , 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
| | - Bernd von Issendorff
- Physikalisches Institut, Universität Freiburg , Stefan-Meier-Straße 21, 79104 Freiburg, Germany
| | - Donald G Truhlar
- Department of Chemistry, Chemical Theory Center, and the Supercomputing Institute, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - J Tobias Lau
- Institut für Methoden und Instrumentierung der Forschung mit Synchrotronstrahlung, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
| | - Michael A Duncan
- Department of Chemistry, University of Georgia , Athens, Georgia 30602, United States
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19
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Ibañez-Azpiroz J, Dos Santos Dias M, Blügel S, Lounis S. Zero-Point Spin-Fluctuations of Single Adatoms. NANO LETTERS 2016; 16:4305-4311. [PMID: 27248465 DOI: 10.1021/acs.nanolett.6b01344] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Stabilizing the magnetic signal of single adatoms is a crucial step toward their successful usage in widespread technological applications such as high-density magnetic data storage devices. The quantum mechanical nature of these tiny objects, however, introduces intrinsic zero-point spin-fluctuations that tend to destabilize the local magnetic moment of interest by dwindling the magnetic anisotropy potential barrier even at absolute zero temperature. Here, we elucidate the origins and quantify the effect of the fundamental ingredients determining the magnitude of the fluctuations, namely, the (i) local magnetic moment, (ii) spin-orbit coupling, and (iii) electron-hole Stoner excitations. Based on a systematic first-principles study of 3d and 4d adatoms, we demonstrate that the transverse contribution of the fluctuations is comparable in size to the magnetic moment itself, leading to a remarkable ≳50% reduction of the magnetic anisotropy energy. Our analysis gives rise to a comprehensible diagram relating the fluctuation magnitude to characteristic features of adatoms, providing practical guidelines for designing magnetically stable nanomagnets with minimal quantum fluctuations.
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Affiliation(s)
- Julen Ibañez-Azpiroz
- Peter Grünberg Institute and Institute for Advanced Simulation, Forschungszentrum Jülich & JARA, D-52425 Jülich, Germany
| | - Manuel Dos Santos Dias
- Peter Grünberg Institute and Institute for Advanced Simulation, Forschungszentrum Jülich & JARA, D-52425 Jülich, Germany
| | - Stefan Blügel
- Peter Grünberg Institute and Institute for Advanced Simulation, Forschungszentrum Jülich & JARA, D-52425 Jülich, Germany
| | - Samir Lounis
- Peter Grünberg Institute and Institute for Advanced Simulation, Forschungszentrum Jülich & JARA, D-52425 Jülich, Germany
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20
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Chen J, Cui H, Wang GQ, Zhou TW, Chen H, Yuan HK. Deposition Morphology and Magnetism of Co, Pt Adatoms and Small CoPt Adclusters on Ni(100) Substrate. J CLUST SCI 2016. [DOI: 10.1007/s10876-016-0976-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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21
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Singh S, Prajapat CL, Bhattacharya D, Ghosh SK, Gonal MR, Basu S. Antiferromagnetic coupling between surface and bulk magnetization and anomalous magnetic transport in electro-deposited cobalt film. RSC Adv 2016. [DOI: 10.1039/c6ra05091c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Correlation of morphology and structure and magnetization depth profiles of Co films grown by two different techniques, e.g. electrodeposition (S1) and sputtering (S2).
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Affiliation(s)
- Surendra Singh
- Solid State Physics Division
- Bhabha Atomic Research Centre
- Mumbai
- India
| | - C. L. Prajapat
- Technical Physics Division
- Bhabha Atomic Research Centre
- Mumbai
- India
| | - D. Bhattacharya
- Solid State Physics Division
- Bhabha Atomic Research Centre
- Mumbai
- India
| | - S. K. Ghosh
- Material Processing Division
- Bhabha Atomic Research Centre
- Mumbai
- India
| | - M. R. Gonal
- Glass and Advanced Material Division
- Bhabha Atomic Research Centre
- Mumbai
- India
| | - S. Basu
- Solid State Physics Division
- Bhabha Atomic Research Centre
- Mumbai
- India
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22
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Dreiser J. Molecular lanthanide single-ion magnets: from bulk to submonolayers. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:183203. [PMID: 25893740 DOI: 10.1088/0953-8984/27/18/183203] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Single-ion magnets (SIMs) are mononuclear molecular complexes exhibiting slow relaxation of magnetization. They are currently attracting a lot of interest because of potential applications in spintronics and quantum information processing. However, exploiting SIMs in, e.g. molecule-inorganic hybrid devices requires a fundamental understanding of the effects of molecule-substrate interactions on the SIM magnetic properties. In this review the properties of lanthanide SIMs in the bulk crystalline phase and deposited on surfaces in the (sub)monolayer regime are discussed. As a starting point trivalent lanthanide ions in a ligand field will be described, and the challenges in characterizing the ligand field are illustrated with a focus on several spectroscopic techniques which are able to give direct information on the ligand-field split energy levels. Moreover, the dominant mechanisms of magnetization relaxation in the bulk phase are discussed followed by an overview of SIMs relevant for surface deposition. Further, a short introduction will be given on x-ray absorption spectroscopy, x-ray magnetic circular dichroism and scanning tunneling microscopy. Finally, the recent experiments on surface-deposited SIMs will be reviewed, along with a discussion of future perspectives.
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Affiliation(s)
- J Dreiser
- Ecole Polytechnique Fédérale de Lausanne, ICMP, Station 3, CH-1015 Lausanne, Switzerland. Paul Scherrer Institut, Swiss Light Source, CH-5232 Villigen PSI, Switzerland
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23
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Dubout Q, Donati F, Wäckerlin C, Calleja F, Etzkorn M, Lehnert A, Claude L, Gambardella P, Brune H. Controlling the spin of co atoms on pt(111) by hydrogen adsorption. PHYSICAL REVIEW LETTERS 2015; 114:106807. [PMID: 25815958 DOI: 10.1103/physrevlett.114.106807] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Indexed: 06/04/2023]
Abstract
We investigate the effect of H adsorption on the magnetic properties of individual Co atoms on Pt(111) with scanning tunneling microscopy. For pristine Co atoms, we detect no inelastic features in the tunnel spectra. Conversely, CoH and CoH2 show a number of low-energy vibrational features in their differential conductance identified by isotope substitution. Only the fcc-adsorbed species present conductance steps of magnetic origin, with a field splitting identifying their effective spin as Seff=2 for CoH and 3/2 for CoH2. The exposure to H2 and desorption through tunnel electrons allow the reversible control of the spin in half-integer steps. Because of the presence of the surface, the hydrogen-induced spin increase is opposite to the spin sequence of CoHn molecules in the gas phase.
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Affiliation(s)
- Q Dubout
- Institute of Condensed Matter Physics (ICMP), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - F Donati
- Institute of Condensed Matter Physics (ICMP), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - C Wäckerlin
- Institute of Condensed Matter Physics (ICMP), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - F Calleja
- Institute of Condensed Matter Physics (ICMP), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
- Madrid Institute for Advanced Studies, IMDEA Nanoscience, Calle Faraday 9, Campus Cantoblanco, E-28049 Madrid, Spain
| | - M Etzkorn
- Institute of Condensed Matter Physics (ICMP), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany
| | - A Lehnert
- Institute of Condensed Matter Physics (ICMP), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - L Claude
- Institute of Condensed Matter Physics (ICMP), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - P Gambardella
- Institute of Condensed Matter Physics (ICMP), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
- Department of Materials, ETH Zürich, Hönggerbergring 64, CH-8093 Zürich, Switzerland
| | - H Brune
- Institute of Condensed Matter Physics (ICMP), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
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24
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Zhang Y, Zhu G, Lu J, Guo Z, Cao J. Graphyne as a promising substrate for high density magnetic storage bits. RSC Adv 2015. [DOI: 10.1039/c5ra18767b] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Applying magnetic nanostructures in high density magnetic data storage is hindered by a lack of suitable substrate.
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Affiliation(s)
- Yun Zhang
- Department of Physics
- Xiangtan University
- Xiangtan
- China
- Department of Physics and Information Technology
| | - Guojun Zhu
- Department of Physics
- Xiangtan University
- Xiangtan
- China
| | - Jinlian Lu
- Department of Physics
- Xiangtan University
- Xiangtan
- China
| | - Zhixin Guo
- Department of Physics
- Xiangtan University
- Xiangtan
- China
| | - Juexian Cao
- Department of Physics
- Xiangtan University
- Xiangtan
- China
- Beijing Computational Science Research Center
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25
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Fransson J, Ren J, Zhu JX. Electrical and thermal control of magnetic exchange interactions. PHYSICAL REVIEW LETTERS 2014; 113:257201. [PMID: 25554904 DOI: 10.1103/physrevlett.113.257201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Indexed: 06/04/2023]
Abstract
We investigate the far-from-equilibrium nature of magnetic anisotropy and exchange interactions between molecular magnets embedded in a tunnel junction. By mapping to an effective spin model, these magnetic interactions can be divided into three types: isotropic Heisenberg, anisotropic Ising, and anisotropic Dzyaloshinski-Moriya contributions, which are attributed to the background nonequilibrium electronic structures. We further demonstrate that both the magnetic self- and exchange interactions can be controlled either electrically by gating and tuning the voltage bias, or thermally by adjusting the temperature bias. We show that the Heisenberg and Ising interactions scale linearly, while the Dzyaloshinski-Moriya interaction scales quadratically, with the molecule-lead coupling strength. The interactions scale linearly with the effective spin polarizations of the leads and the molecular coherence. Our results pave a way for smart control of magnetic exchange interactions at atomic and molecular levels.
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Affiliation(s)
- Jonas Fransson
- Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
| | - Jie Ren
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Jian-Xin Zhu
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA and Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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26
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Lounis S. Non-collinear magnetism induced by frustration in transition-metal nanostructures deposited on surfaces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:273201. [PMID: 24918578 DOI: 10.1088/0953-8984/26/27/273201] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
How does magnetism behave when the physical dimension is reduced to the size of nanostructures? The multiplicity of magnetic states in these systems can be very rich, in that their properties depend on the atomic species, the cluster size, shape and symmetry or choice of the substrate. Small variations of the cluster parameters may change the properties dramatically. Research in this field has gained much by the many novel experimental methods and techniques exhibiting atomic resolution. Here we review the ab-initio approach, focusing on recent calculations on magnetic frustration and occurrence of non-collinear magnetism in antiferromagnetic nanostructures deposited on surfaces.
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Affiliation(s)
- S Lounis
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich & JARA, 52425 Jülich, Germany
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27
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Šipr O, Bornemann S, Ebert H, Minár J. Magnetocrystalline anisotropy energy for adatoms and monolayers on non-magnetic substrates: where does it come from? JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:196002. [PMID: 24762802 DOI: 10.1088/0953-8984/26/19/196002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The substrate contribution to the magnetic anisotropy energy (MAE) of supported nanostructures can be assessed by a site-selective manipulation of the spin-orbit coupling (SOC) and of the effective exchange field Bex. A systematic study of Co adatoms and Co monolayers on the (1 1 1) surfaces of Cu, Ag, Au, Pd and Pt is performed to study common trends in this class of materials. It is found that for adatoms, the influence of the substrate SOC and Bex is relatively small (10-30% of the MAE) while for monolayers, this influence can be substantial. The influence of the substrate SOC is much more important than the influence of the substrate Bex, except for highly polarizable substrates with a strong SOC (such as Pt). The substrate always promotes the tendency to an out-of-plane orientation of the easy magnetic axis for all the investigated systems.
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Affiliation(s)
- O Šipr
- Institute of Physics of the ASCR vvi, Cukrovarnická 10, CZ-162 53 Prague, Czech Republic
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28
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Rajeswari J, Ibach H, Schneider CM. Standing spin waves in ultrathin magnetic films: a method to test for layer-dependent exchange coupling. PHYSICAL REVIEW LETTERS 2014; 112:127202. [PMID: 24724676 DOI: 10.1103/physrevlett.112.127202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2013] [Indexed: 06/03/2023]
Abstract
We introduce a method to test theoretical models for the layer dependence of exchange coupling constants in ultrathin magnetic films. The method is based on the observation of high-energy and high-momentum standing spin wave modes using high-resolution electron energy loss spectroscopy. Experimental data are presented for 5-8 layers of fcc cobalt deposited on Cu(100). The power of the method is illustrated by comparison to two theoretical studies predicting rather different results concerning the ratio of the interlayer and intralayer exchange coupling constants near the surface. Only the theory with a large interlayer coupling shows sufficient energy spreading in the layer dependence of the dispersion curves to match the experimental data. We furthermore discuss the reason for the surprising success of the simple nearest-neighbor Heisenberg model with a single exchange constant matched to experiment.
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Affiliation(s)
- J Rajeswari
- Peter Grünberg Institut (PGI-6), Forschungszentrum Jülich, 52425 Jülich, Germany and Jülich Aachen Research Alliance, 52425 Jülich, Germany
| | - H Ibach
- Jülich Aachen Research Alliance, 52425 Jülich, Germany and Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
| | - C M Schneider
- Peter Grünberg Institut (PGI-6), Forschungszentrum Jülich, 52425 Jülich, Germany and Jülich Aachen Research Alliance, 52425 Jülich, Germany
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29
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Brovko OO, Ruiz-Díaz P, Dasa TR, Stepanyuk VS. Controlling magnetism on metal surfaces with non-magnetic means: electric fields and surface charging. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:093001. [PMID: 24523356 DOI: 10.1088/0953-8984/26/9/093001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We review the state of the art of surface magnetic property control with non-magnetic means, concentrating on metallic surfaces and techniques such as charge-doping or external electric field (EEF) application. Magneto-electric coupling via EEF-based charge manipulation is discussed as a way to tailor single adatom spins, exchange interaction between adsorbates or anisotropies of layered systems. The mechanisms of paramagnetic and spin-dependent electric field screening and the effect thereof on surface magnetism are discussed in the framework of theoretical and experimental studies. The possibility to enhance the effect of EEF by immersing the target system into an electrolyte or ionic liquid is discussed by the example of substitutional impurities and metallic alloy multilayers. A similar physics is pointed out for the case of charge traps, metallic systems decoupled from a bulk electron bath. In that case the charging provides the charge carrier density changes necessary to affect the magnetic moments and anisotropies in the system. Finally, the option of using quasi-free electrons rather than localized atomic spins for surface magnetism control is discussed with the example of Shockley-type metallic surface states confined to magnetic nanoislands.
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Affiliation(s)
- Oleg O Brovko
- Max-Planck Institut für Mikrostrukturphysik, Halle, Germany
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30
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Oberg JC, Calvo MR, Delgado F, Moro-Lagares M, Serrate D, Jacob D, Fernández-Rossier J, Hirjibehedin CF. Control of single-spin magnetic anisotropy by exchange coupling. NATURE NANOTECHNOLOGY 2014; 9:64-8. [PMID: 24317285 DOI: 10.1038/nnano.2013.264] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2013] [Accepted: 11/08/2013] [Indexed: 05/12/2023]
Abstract
The properties of quantum systems interacting with their environment, commonly called open quantum systems, can be affected strongly by this interaction. Although this can lead to unwanted consequences, such as causing decoherence in qubits used for quantum computation, it can also be exploited as a probe of the environment. For example, magnetic resonance imaging is based on the dependence of the spin relaxation times of protons in water molecules in a host's tissue. Here we show that the excitation energy of a single spin, which is determined by magnetocrystalline anisotropy and controls its stability and suitability for use in magnetic data-storage devices, can be modified by varying the exchange coupling of the spin to a nearby conductive electrode. Using scanning tunnelling microscopy and spectroscopy, we observe variations up to a factor of two of the spin excitation energies of individual atoms as the strength of the spin's coupling to the surrounding electronic bath changes. These observations, combined with calculations, show that exchange coupling can strongly modify the magnetic anisotropy. This system is thus one of the few open quantum systems in which the energy levels, and not just the excited-state lifetimes, can be renormalized controllably. Furthermore, we demonstrate that the magnetocrystalline anisotropy, a property normally determined by the local structure around a spin, can be tuned electronically. These effects may play a significant role in the development of spintronic devices in which an individual magnetic atom or molecule is coupled to conducting leads.
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Affiliation(s)
- Jenny C Oberg
- 1] London Centre for Nanotechnology, University College London, London WC1H 0AH, UK [2] Department of Physics and Astronomy, University College London, London WC1E 6BT, UK [3]
| | - M Reyes Calvo
- 1] London Centre for Nanotechnology, University College London, London WC1H 0AH, UK [2] [3]
| | - Fernando Delgado
- International Iberian Nanotechnology Laboratory, 4715-330 Braga, Portugal
| | - María Moro-Lagares
- 1] Instituto de Nanociencia de Aragón and Laboratorio de Microscopías Avanzadas, Universidad de Zaragoza, 50018 Zaragoza, Spain [2] Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50009 Zaragoza, Spain
| | - David Serrate
- 1] Instituto de Nanociencia de Aragón and Laboratorio de Microscopías Avanzadas, Universidad de Zaragoza, 50018 Zaragoza, Spain [2] Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50009 Zaragoza, Spain
| | - David Jacob
- Max-Planck-Institut für Mikrostrukturphysik, 06120 Halle, Germany
| | | | - Cyrus F Hirjibehedin
- 1] London Centre for Nanotechnology, University College London, London WC1H 0AH, UK [2] Department of Physics and Astronomy, University College London, London WC1E 6BT, UK [3] Department of Chemistry, University College London, London WC1H 0AJ, UK
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31
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Choi H, Lee M, Kim S, Lee KR, Chung YC. Detecting gas molecules via atomic magnetization. Dalton Trans 2014; 43:13070-5. [DOI: 10.1039/c4dt01401d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Adsorptions of gas molecules were found to alter the directions and magnitudes of magnetic moments of transition metal (Co, Fe) atoms adsorbed on graphene.
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Affiliation(s)
- Heechae Choi
- Center for Computational Science
- Korea Institute of Science and Technology
- Seoul 136-791, Korea
- Department of Materials Science and Engineering
- Hanyang University
| | - Minho Lee
- Department of Materials Science and Engineering
- Hanyang University
- Seoul 133-791, Korea
| | - Seungchul Kim
- Center for Computational Science
- Korea Institute of Science and Technology
- Seoul 136-791, Korea
| | - Kwang-Ryeol Lee
- Center for Computational Science
- Korea Institute of Science and Technology
- Seoul 136-791, Korea
| | - Yong-Chae Chung
- Department of Materials Science and Engineering
- Hanyang University
- Seoul 133-791, Korea
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32
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Miyamachi T, Schuh T, Märkl T, Bresch C, Balashov T, Stöhr A, Karlewski C, André S, Marthaler M, Hoffmann M, Geilhufe M, Ostanin S, Hergert W, Mertig I, Schön G, Ernst A, Wulfhekel W. Stabilizing the magnetic moment of single holmium atoms by symmetry. Nature 2013; 503:242-6. [DOI: 10.1038/nature12759] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Accepted: 10/09/2013] [Indexed: 11/09/2022]
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33
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Bezerra-Neto MM, Ribeiro MS, Sanyal B, Bergman A, Muniz RB, Eriksson O, Klautau AB. Complex magnetic structure of clusters and chains of Ni and Fe on Pt(111). Sci Rep 2013; 3:3054. [PMID: 24165828 PMCID: PMC3810666 DOI: 10.1038/srep03054] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Accepted: 09/13/2013] [Indexed: 11/30/2022] Open
Abstract
We present an approach to control the magnetic structure of adatoms adsorbed on a substrate having a high magnetic susceptibility. Using finite Ni-Pt and Fe-Pt nanowires and nanostructures on Pt(111) surfaces, our ab initio results show that it is possible to tune the exchange interaction and magnetic configuration of magnetic adatoms (Fe or Ni) by introducing different numbers of Pt atoms to link them, or by including edge effects. The exchange interaction between Ni (or Fe) adatoms on Pt(111) can be considerably increased by introducing Pt chains to link them. The magnetic ordering can be regulated allowing for ferromagnetic or antiferromagnetic configurations. Noncollinear magnetic alignments can also be stabilized by changing the number of Pt-mediated atoms. An Fe-Pt triangularly-shaped nanostructure adsorbed on Pt(111) shows the most complex magnetic structure of the systems considered here: a spin-spiral type of magnetic order that changes its propagation direction at the triangle vertices.
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Khajetoorians AA, Schlenk T, Schweflinghaus B, Dias MDS, Steinbrecher M, Bouhassoune M, Lounis S, Wiebe J, Wiesendanger R. Spin excitations of individual Fe atoms on Pt(111): impact of the site-dependent giant substrate polarization. PHYSICAL REVIEW LETTERS 2013; 111:157204. [PMID: 24160625 DOI: 10.1103/physrevlett.111.157204] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2013] [Indexed: 06/02/2023]
Abstract
We demonstrate using inelastic scanning tunneling spectroscopy and simulations based on density functional theory that the amplitude and sign of the magnetic anisotropy energy for a single Fe atom adsorbed onto the Pt(111) surface can be manipulated by modifying the adatom binding site. Since the magnitude of the measured anisotropy is remarkably small, up to an order of magnitude smaller than previously reported, electron-hole excitations are weak and thus the spin excitation exhibits long lived precessional lifetimes compared to the values found for the same adatom on noble metal surfaces.
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Affiliation(s)
- A A Khajetoorians
- Institute of Applied Physics, Universität Hamburg, D-20355 Hamburg, Germany
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35
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Bryant B, Spinelli A, Wagenaar JJT, Gerrits M, Otte AF. Local control of single atom magnetocrystalline anisotropy. PHYSICAL REVIEW LETTERS 2013; 111:127203. [PMID: 24093296 DOI: 10.1103/physrevlett.111.127203] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Indexed: 06/02/2023]
Abstract
Individual Fe atoms on a Cu(2)N/Cu(100) surface exhibit strong magnetic anisotropy due to the crystal field. We show that we can controllably enhance or reduce this anisotropy by adjusting the relative position of a second nearby Fe atom, with atomic precision, in a low-temperature scanning tunneling microscope. Local inelastic electron tunneling spectroscopy, combined with a qualitative first-principles model, reveal that the change in uniaxial anisotropy is driven by local strain due to the presence of the second Fe atom.
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Affiliation(s)
- B Bryant
- Department of Quantum Nanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
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36
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Holzberger S, Schuh T, Blügel S, Lounis S, Wulfhekel W. Parity effect in the ground state localization of antiferromagnetic chains coupled to a ferromagnet. PHYSICAL REVIEW LETTERS 2013; 110:157206. [PMID: 25167307 DOI: 10.1103/physrevlett.110.157206] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2012] [Revised: 01/13/2013] [Indexed: 06/03/2023]
Abstract
We investigate the ground states of antiferromagnetic Mn nanochains on Ni(110) by spin-polarized scanning tunneling microscopy in combination with theory. While the ferrimagnetic linear trimer experimentally shows the predicted collinear classical ground state, no magnetic contrast was observed for dimers and tetramers where noncollinear structures were expected based on ab initio theory. This striking observation can be explained by zero-point energy motion for even-numbered chains derived within a classical equation of motion leading to nonclassical ground states. Thus, depending on the parity of the chain length, the system shows a classical or a quantum behavior.
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Affiliation(s)
- Simon Holzberger
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany
| | - Tobias Schuh
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany
| | - Stefan Blügel
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Samir Lounis
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Wulf Wulfhekel
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany
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37
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Schuh T, Miyamachi T, Gerstl S, Geilhufe M, Hoffmann M, Ostanin S, Hergert W, Ernst A, Wulfhekel W. Magnetic excitations of rare earth atoms and clusters on metallic surfaces. NANO LETTERS 2012; 12:4805-4809. [PMID: 22906055 DOI: 10.1021/nl302250n] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Magnetic anisotropy and magnetization dynamics of rare earth Gd atoms and dimers on Pt(111) and Cu(111) were investigated with inelastic tunneling spectroscopy. The spin excitation spectra reveal that giant magnetic anisotropies and lifetimes of the excited states of Gd are nearly independent of the supporting surfaces and the cluster size. In combination with theoretical calculations, we argue that the observed features are caused by strongly localized character of 4f electrons in Gd atoms and clusters.
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Affiliation(s)
- Tobias Schuh
- Karlsruhe Institute of Technology, Physikalisches Institut, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe, Germany
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38
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Zhang Y, Chuang TH, Zakeri K, Kirschner J. Relaxation time of terahertz magnons excited at ferromagnetic surfaces. PHYSICAL REVIEW LETTERS 2012; 109:087203. [PMID: 23002772 DOI: 10.1103/physrevlett.109.087203] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Indexed: 06/01/2023]
Abstract
The temporal and spatial properties of terahertz magnons excited at ferromagnetic fcc Co(100) and bcc Fe(110) surfaces are investigated experimentally. The magnon lifetime is found to be a few tens of femtoseconds at low wave vectors, which reduces significantly as the wave vector approaches the Brillouin zone boundary. Surprisingly, the lifetime is very similar in both systems, in spite of the fact that the excitation energy in the Co(100) film is by a factor of two larger than in the Fe(110) film. The magnon wave packets propagate only a few nanometers within their lifetime. In addition to the fact that our results describe the damping mechanism in ultrafast time scales, they may provide a way to predict the ultimate time scale of magnetic switching in nanostructures.
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Affiliation(s)
- Y Zhang
- Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany.
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39
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Bauer DSG, Mavropoulos P, Lounis S, Blügel S. Thermally activated magnetization reversal in monatomic magnetic chains on surfaces studied by classical atomistic spin-dynamics simulations. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:394204. [PMID: 21921308 DOI: 10.1088/0953-8984/23/39/394204] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We analyse the spontaneous magnetization reversal of supported monatomic chains of finite length due to thermal fluctuations via atomistic spin-dynamics simulations. Our approach is based on the integration of the Landau-Lifshitz equation of motion of a classical spin Hamiltonian in the presence of stochastic forces. The associated magnetization lifetime is found to obey an Arrhenius law with an activation barrier equal to the domain wall energy in the chain. For chains longer than one domain wall width, the reversal is initiated by nucleation of a reversed magnetization domain primarily at the chain edge followed by a subsequent propagation of the domain wall to the other edge in a random-walk fashion. This results in a linear dependence of the lifetime on the chain length, if the magnetization correlation length is not exceeded. We studied chains of uniaxial and triaxial anisotropy and found that a triaxial anisotropy leads to a reduction of the magnetization lifetime due to a higher reversal attempt rate, even though the activation barrier is not changed.
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Affiliation(s)
- David S G Bauer
- Institut für Festkörperforschung, Institute for Advanced Simulation, and JARA, Forschungszentrum Jülich, D-52425 Jülich, Germany
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40
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Zhang L, Miyamachi T, Tomanić T, Dehm R, Wulfhekel W. A compact sub-Kelvin ultrahigh vacuum scanning tunneling microscope with high energy resolution and high stability. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2011; 82:103702. [PMID: 22047298 DOI: 10.1063/1.3646468] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We designed a scanning tunneling microscope working at sub-Kelvin temperatures in ultrahigh vacuum (UHV) in order to study the magnetic properties on the nanoscale. An entirely homebuilt three-stage cryostat is used to cool down the microscope head. The first stage is cooled with liquid nitrogen, the second stage with liquid (4)He. The third stage uses a closed-cycle Joule-Thomson refrigerator of a cooling power of 1 mW. A base temperature of 930 mK at the microscope head was achieved using expansion of (4)He, which can be reduced to ≈400 mK when using (3)He. The cryostat has a low liquid helium consumption of only 38 ml/h and standing times of up to 280 h. The fast cooling down of the samples (3 h) guarantees high sample throughput. Test experiments with a superconducting tip show a high energy resolution of 0.3 meV when performing scanning tunneling spectroscopy. The vertical stability of the tunnel junction is well below 1 pm (peak to peak) and the electric noise floor of tunneling current is about 6fA/√Hz. Atomic resolution with a tunneling current of 1 pA and 1 mV was achieved on Au(111). The lateral drift of the microscope at stable temperature is below 20 pm/h. A superconducting spilt-coil magnet allows to apply an out-of-plane magnetic field of up to 3 T at the sample surface. The flux vortices of a Nb(110) sample were clearly resolved in a map of differential conductance at 1.1 K and a magnetic field of 0.21 T. The setup is designed for in situ preparation of tip and samples under UHV condition.
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Affiliation(s)
- L Zhang
- Physikalisches Institut, Karlsruhe Institute of Technology, Karlsruhe, Germany
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41
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Gawronski H, Fransson J, Morgenstern K. Real-space imaging of inelastic Friedel-like surface oscillations emerging from molecular adsorbates. NANO LETTERS 2011; 11:2720-2724. [PMID: 21639119 DOI: 10.1021/nl201076g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We report real space imaging measurements of inelastic Friedel oscillations. The inelastic electron tunneling spectroscopy, using scanning tunneling microscopy, around dimers of dichlorobenze adsorbates on Au(111) surface display clear spatial modulations that we attribute to inelastic scattering at the molecular sites caused by molecular vibrations. Due to local interactions between the adsorbate and the surface states, the molecular vibrations generate a redistribution of the charge density at energies in a narrow range around the inelastic mode. Our experimental findings are supported by theoretical arguments.
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Affiliation(s)
- Heiko Gawronski
- Division for Atomic and Molecular Structures (ATMOS), Institute for Solid State Physics, Leibniz University of Hannover, Appelstrasse 2, D-30167 Hannover, Germany
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Khajetoorians AA, Lounis S, Chilian B, Costa AT, Zhou L, Mills DL, Wiebe J, Wiesendanger R. Itinerant nature of atom-magnetization excitation by tunneling electrons. PHYSICAL REVIEW LETTERS 2011; 106:037205. [PMID: 21405293 DOI: 10.1103/physrevlett.106.037205] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2010] [Indexed: 05/30/2023]
Abstract
We have performed single-atom magnetization curve (SAMC) measurements and inelastic scanning tunneling spectroscopy (ISTS) on individual Fe atoms on a Cu(111) surface. The SAMCs show a broad distribution of magnetic moments with 3.5 μB being the mean value. ISTS reveals a magnetization excitation with a lifetime of 200 fsec which decreases by a factor of 2 upon application of a magnetic field of 12 T. The experimental observations are quantitatively explained by the decay of the magnetization excitation into Stoner modes of the itinerant electron system as shown by newly developed theoretical modeling.
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Affiliation(s)
- A A Khajetoorians
- Institute of Applied Physics, Hamburg University, Jungiusstrasse 11, D-20355 Hamburg, Germany
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Lounis S, Costa AT, Muniz RB, Mills DL. Dynamical magnetic excitations of nanostructures from first principles. PHYSICAL REVIEW LETTERS 2010; 105:187205. [PMID: 21231134 DOI: 10.1103/physrevlett.105.187205] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2010] [Indexed: 05/30/2023]
Abstract
Within time-dependent density functional theory, combined with the Korringa-Kohn-Rostoker Green functions, we devise a real space method to investigate spin dynamics. Our scheme enables one to deduce the Coulomb potential which assures a proper Goldstone mode is present. We illustrate with application to 3d adatoms and dimers on Cu(100).
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Affiliation(s)
- S Lounis
- Department of Physics and Astronomy, University of California Irvine, California 92697, USA.
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44
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Detecting excitation and magnetization of individual dopants in a semiconductor. Nature 2010; 467:1084-7. [DOI: 10.1038/nature09519] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2010] [Accepted: 09/10/2010] [Indexed: 11/08/2022]
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45
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Brede J, Atodiresei N, Kuck S, Lazić P, Caciuc V, Morikawa Y, Hoffmann G, Blügel S, Wiesendanger R. Spin- and energy-dependent tunneling through a single molecule with intramolecular spatial resolution. PHYSICAL REVIEW LETTERS 2010; 105:047204. [PMID: 20867880 DOI: 10.1103/physrevlett.105.047204] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2010] [Indexed: 05/29/2023]
Abstract
We investigate the spin- and energy-dependent tunneling through a single organic molecule (CoPc) adsorbed on a ferromagnetic Fe thin film, spatially resolved by low-temperature spin-polarized scanning tunneling microscopy. Interestingly, the metal ion as well as the organic ligand show a significant spin dependence of tunneling current flow. State-of-the-art ab initio calculations including also van der Waals interactions reveal a strong hybridization of molecular orbitals and substrate 3d states. The molecule is anionic due to a transfer of one electron, resulting in a nonmagnetic (S=0) state. Nevertheless, tunneling through the molecule exhibits a pronounced spin dependence due to spin-split molecule-surface hybrid states.
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Affiliation(s)
- Jens Brede
- Institute of Applied Physics, University of Hamburg, 20355 Hamburg, Germany
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46
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Błoński P, Hafner J. Density-functional theory of the magnetic anisotropy of nanostructures: an assessment of different approximations. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:426001. [PMID: 21715860 DOI: 10.1088/0953-8984/21/42/426001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We discuss the multiple technical choices that have to be made in ab initio density-functional calculations of the magnetic anisotropy of supported nanostructures: (i) choice of the exchange-correlation functional, (ii) degree of optimization of the geometry of the adsorbate/substrate complex, (iii) magnetic anisotropy energy calculated self-consistently or via the 'force theorem', (iv) calculations based on slab models of the substrate or using a Green's function describing a semi-infinite substrate, (v) full potential approach or atomic-sphere approximation. Using isolated Fe and Co atoms on Pt(111) as an example we demonstrate that by using a judicious combination of relatively crude approximations (complete neglect of structural relaxation, local exchange-correlation functional,...) seemingly good agreement with experimental anisotropy energies can be achieved, while the calculated orbital moments remain small. At a higher level of theory (relaxed adsorbate/substrate complex, gradient-corrected functionals,...) providing a realistic geometry of the adsorbate/substrate complex and hence a correct description of the interaction between the magnetic adatom and its ligands, anisotropy energies are also in semi-quantitative agreement with experiment, while the orbital moments of the adatoms are much too small. We suggest that the anisotropy energies provided by both approaches should be considered as lower limits of the real anisotropies. Without relaxation the ligand effect coupling the orbital moments of the adatom to the heavy atoms of the substrate is underestimated, while in a relaxed adsorbate/substrate complex the lack of orbital dependence of the exchange potential combined with a strong hybridization of adatom and substrate states leads to a strong underestimation of the orbital moment. We have briefly explored the influence of post-density-functional corrections. Adding a modest on-site Coulomb repulsion to the d states of the adatom (in a DFT+U approach) leads to a modest increase of spin and orbital moments of the adatom accompanied by a slow decrease of the induced moments, leaving the anisotropy energy almost unchanged.
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Affiliation(s)
- Piotr Błoński
- Fakultät für Physik and Center for Computational Materials Science, Universität Wien, Sensengasse 8/12, A-1090 Wien, Austria
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