1
|
Huang HL, Jeng HT. Orbital ordering and magnetism in layered Perovskite Ruthenate Sr 2RuO 4. Sci Rep 2020; 10:7089. [PMID: 32341446 PMCID: PMC7184627 DOI: 10.1038/s41598-020-63415-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2019] [Accepted: 03/31/2020] [Indexed: 11/17/2022] Open
Abstract
Local density approximation plus on-site Coulomb interaction U electronic structure calculations reveal that layered perovskite oxide Sr2RuO4 exhibits the ferromagnetic (FM) half-metallic ground state, which is nearly degenerate with the antiferromagnetic (AFM) phase with a slightly higher total energy. The nearly degenerate FM/AFM total energies provide a reasonable explanation for the experimentally observed spin-fluctuation. In addition, a dumbbell-shape 4d − t2g recombined dxz − dyz orbital ordering on the Ru sublattice is obtained owing to the on-site Coulomb interaction U associated with the elongated RuO6 octahedron local structure. The discovered orbital ordering is robust against the spin-orbit interaction as well as the surface terminations. Our findings unravel the on-site Coulomb correlation as the driving force of the Ru-4d orbital ordering as well as the inherent magnetic degeneracy.
Collapse
Affiliation(s)
- Hung-Lung Huang
- Department of Physics, National Tsing Hua University, Hsinchu, 30013, Taiwan
| | - Horng-Tay Jeng
- Department of Physics, National Tsing Hua University, Hsinchu, 30013, Taiwan. .,Physics Division, National Center for Theoretical Sciences, Hsinchu, 30013, Taiwan. .,Institute of Physics, Academia Sinica, Taipei, 11529, Taiwan.
| |
Collapse
|
2
|
Romming N, Pralow H, Kubetzka A, Hoffmann M, von Malottki S, Meyer S, Dupé B, Wiesendanger R, von Bergmann K, Heinze S. Competition of Dzyaloshinskii-Moriya and Higher-Order Exchange Interactions in Rh/Fe Atomic Bilayers on Ir(111). PHYSICAL REVIEW LETTERS 2018; 120:207201. [PMID: 29864327 DOI: 10.1103/physrevlett.120.207201] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 02/27/2018] [Indexed: 06/08/2023]
Abstract
Using spin-polarized scanning tunneling microscopy and density functional theory we demonstrate the occurrence of a novel type of noncollinear spin structure in Rh/Fe atomic bilayers on Ir(111). We find that higher-order exchange interactions depend sensitively on the stacking sequence. For fcc-Rh/Fe/Ir(111), frustrated exchange interactions are dominant and lead to the formation of a spin spiral ground state with a period of about 1.5 nm. For hcp-Rh/Fe/Ir(111), higher-order exchange interactions favor an up-up-down-down (↑↑↓↓) state. However, the Dzyaloshinskii-Moriya interaction at the Fe/Ir interface leads to a small angle of about 4° between adjacent magnetic moments resulting in a canted ↑↑↓↓ ground state.
Collapse
Affiliation(s)
- Niklas Romming
- Department of Physics, University of Hamburg, 20355 Hamburg, Germany
| | - Henning Pralow
- Institut für Theoretische und Astrophysik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany
| | - André Kubetzka
- Department of Physics, University of Hamburg, 20355 Hamburg, Germany
| | - Markus Hoffmann
- Institut für Theoretische und Astrophysik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Stephan von Malottki
- Institut für Theoretische und Astrophysik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany
| | - Sebastian Meyer
- Institut für Theoretische und Astrophysik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany
| | - Bertrand Dupé
- Institut für Theoretische und Astrophysik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany
- Institute of Physics, Johannes Gutenberg-Universität Mainz, Staudingerweg 7, 55128 Mainz, Germany
| | | | | | - Stefan Heinze
- Institut für Theoretische und Astrophysik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany
| |
Collapse
|
3
|
Abstract
Skyrmions are topologically protected non-collinear magnetic structures. Their stability is ideally suited to carry information in, e.g., racetrack memories. The success of such a memory critically depends on the ability to stabilize and manipulate skyrmions at low magnetic fields. The non-collinear Dzyaloshinskii-Moriya interaction originating from spin-orbit coupling drives skyrmion formation. It competes with Heisenberg exchange and magnetic anisotropy favoring collinear states. Isolated skyrmions in ultra-thin films so far required magnetic fields as high as several Tesla. Here, we show that isolated skyrmions in a monolayer of Co/Ru(0001) can be stabilized down to vanishing fields. Even with the weak spin-orbit coupling of the 4d element Ru, homochiral spin spirals and isolated skyrmions were detected with spin-sensitive scanning tunneling microscopy. Density functional theory calculations explain the stability of the chiral magnetic features by the absence of magnetic anisotropy energy. Skyrmions are promising for spintronics but usually require large spin-orbit coupling of 5d-metals and external magnetic field. Here the authors realize stabilization of isolated skyrmions at a 4d-metal interface of weak chiral interaction and magnetic anisotropy down to vanishing field.
Collapse
|
4
|
Phark SH, Sander D. Spin-polarized scanning tunneling microscopy with quantitative insights into magnetic probes. NANO CONVERGENCE 2017; 4:8. [PMID: 28725524 PMCID: PMC5486209 DOI: 10.1186/s40580-017-0102-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Accepted: 03/29/2017] [Indexed: 05/25/2023]
Abstract
Spin-polarized scanning tunneling microscopy and spectroscopy (spin-STM/S) have been successfully applied to magnetic characterizations of individual nanostructures. Spin-STM/S is often performed in magnetic fields of up to some Tesla, which may strongly influence the tip state. In spite of the pivotal role of the tip in spin-STM/S, the contribution of the tip to the differential conductance dI/dV signal in an external field has rarely been investigated in detail. In this review, an advanced analysis of spin-STM/S data measured on magnetic nanoislands, which relies on a quantitative magnetic characterization of tips, is discussed. Taking advantage of the uniaxial out-of-plane magnetic anisotropy of Co bilayer nanoisland on Cu(111), in-field spin-STM on this system has enabled a quantitative determination, and thereby, a categorization of the magnetic states of the tips. The resulting in-depth and conclusive analysis of magnetic characterization of the tip opens new venues for a clear-cut sub-nanometer scale spin ordering and spin-dependent electronic structure of the non-collinear magnetic state in bilayer high Fe nanoislands on Cu(111).
Collapse
Affiliation(s)
- Soo-hyon Phark
- Center for Quantum Nanoscience, Institute for Basic Science, Seoul, 03760 Republic of Korea
- Department of Physics, Ewha Womans University, Seoul, 03760 Republic of Korea
| | - Dirk Sander
- Max-Planck-Institut für Mikrostrukturphysik, 06120 Halle, Germany
| |
Collapse
|
5
|
Fischer JA, Sandratskii LM, Phark SH, Ouazi S, Pasa AA, Sander D, Parkin SSP. Probing the spinor nature of electronic states in nanosize non-collinear magnets. Nat Commun 2016; 7:13000. [PMID: 27721384 PMCID: PMC5062547 DOI: 10.1038/ncomms13000] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Accepted: 08/18/2016] [Indexed: 11/12/2022] Open
Abstract
Non-collinear magnetization textures provide a route to novel device concepts in spintronics. These applications require laterally confined non-collinear magnets (NCM). A crucial aspect for potential applications is how the spatial proximity between the NCM and vacuum or another material impacts the magnetization texture on the nanoscale. We focus on a prototypical exchange-driven NCM given by the helical spin order of bilayer Fe on Cu(111). Spin-polarized scanning tunnelling spectroscopy and density functional theory reveal a nanosize- and proximity-driven modification of the electronic and magnetic structure of the NCM in interfacial contact with a ferromagnet or with vacuum. An intriguing non-collinearity between the local magnetization in the sample and the electronic magnetization probed above its surface results. It is a direct consequence of the spinor nature of electronic states in NCM. Our findings provide a possible route for advanced control of nanoscale spin textures by confinement. Non-collinear magnetization textures which are established by chiral exchange interactions have recently provided a route to novel phenomena and device concepts. Here, the authors demonstrate the effects of symmetry breaking on non-collinear magnetization by lateral confinement.
Collapse
Affiliation(s)
- Jeison A Fischer
- Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany.,Laboratório de Filmes Finos e Superfícies, Departamento de Física, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, Brazil
| | | | - Soo-Hyon Phark
- Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany.,Center for Nanometrology, Korea Research Institute of Standards and Science, Daejeon 34113, Korea
| | - Safia Ouazi
- Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany
| | - André A Pasa
- Laboratório de Filmes Finos e Superfícies, Departamento de Física, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, Brazil
| | - Dirk Sander
- Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany
| | - Stuart S P Parkin
- Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany
| |
Collapse
|
6
|
Hsu PJ, Finco A, Schmidt L, Kubetzka A, von Bergmann K, Wiesendanger R. Guiding Spin Spirals by Local Uniaxial Strain Relief. PHYSICAL REVIEW LETTERS 2016; 116:017201. [PMID: 26799040 DOI: 10.1103/physrevlett.116.017201] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Indexed: 06/05/2023]
Abstract
We report on the influence of uniaxial strain relief on the spin spiral state in the Fe double layer grown on Ir(111). Scanning tunneling microscopy (STM) measurements reveal areas with reconstruction lines resulting from uniaxial strain relief due to the lattice mismatch of Fe and Ir atoms, as well as pseudomorphic strained areas. Magnetic field-dependent spin-polarized STM measurements of the reconstructed Fe double layer reveal cycloidal spin spirals with a period on the nm scale. Globally, the spin spiral wave fronts are guided along symmetry-equivalent [112̅] crystallographic directions of the fcc(111) substrate. On an atomic scale the spin spiral propagation direction is linked to the [001] direction of the bcc(110)-like Fe, leading to a zigzag shaped wave front. The isotropically strained pseudomorphic areas also exhibit a preferred magnetic periodicity on the nm scale but no long-range order. We find that already for local strain relief with a single set of reconstruction lines a strict guiding of the spin spiral is realized.
Collapse
Affiliation(s)
- Pin-Jui Hsu
- Department of Physics, University of Hamburg, D-20355 Hamburg, Germany
| | - Aurore Finco
- Department of Physics, University of Hamburg, D-20355 Hamburg, Germany
- Département de physique, École normale supérieure, 45 rue d'Ulm, 75005 Paris, France
| | - Lorenz Schmidt
- Department of Physics, University of Hamburg, D-20355 Hamburg, Germany
| | - André Kubetzka
- Department of Physics, University of Hamburg, D-20355 Hamburg, Germany
| | | | | |
Collapse
|