1
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Das S, Sumedha. Inverse transitions and disappearance of the λ-line in the asymmetric random-field Ising and Blume-Capel models. Phys Rev E 2023; 108:L042101. [PMID: 37978665 DOI: 10.1103/physreve.108.l042101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2023] [Accepted: 10/06/2023] [Indexed: 11/19/2023]
Abstract
We report on reentrance in the random-field Ising and Blume-Capel models, induced by an asymmetric bimodal random-field distribution. The conventional continuous line of transitions between the paramagnetic and ferromagnetic phases, the λ-line, is wiped away by the asymmetry. The phase diagram, then, consists of only first-order transition lines that always end at ordered critical points. We find that, while for symmetric random-field distributions there is no reentrance, the asymmetry in the random-field results in a range of temperatures for which magnetization shows reentrance. While this does not give rise to an inverse transition in the Ising model, for the Blume-Capel model, however, there is a line of first-order inverse phase transitions that ends at an inverse-ordered critical point. We show that the location of the inverse transitions can be inferred from the ground-state phase diagram of the model.
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Affiliation(s)
- Santanu Das
- School of Physical Sciences, National Institute of Science Education and Research, Jatni 752050, India and Homi Bhabha National Institute, Training School Complex, Anushakti Nagar 400094, India
| | - Sumedha
- School of Physical Sciences, National Institute of Science Education and Research, Jatni 752050, India and Homi Bhabha National Institute, Training School Complex, Anushakti Nagar 400094, India
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2
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Yang S, Ju TS, Kim C, Kim HJ, An K, Moon KW, Park S, Hwang C. Magnetic Field Magnitudes Needed for Skyrmion Generation in a General Perpendicularly Magnetized Film. NANO LETTERS 2022; 22:8430-8436. [PMID: 36282733 PMCID: PMC9650724 DOI: 10.1021/acs.nanolett.2c02268] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Revised: 10/08/2022] [Indexed: 06/16/2023]
Abstract
Due to its topological protection, the magnetic skyrmion has been intensively studied for both fundamental aspects and spintronics applications. However, despite recent advancements in skyrmion research, the deterministic creation of isolated skyrmions in a generic perpendicularly magnetized film is still one of the most essential and challenging techniques. Here, we present a method to create magnetic skyrmions in typical perpendicular magnetic anisotropy (PMA) films by applying a magnetic field pulse and a method to determine the magnitude of the required external magnetic fields. Furthermore, to demonstrate the usefulness of this result for future skyrmion research, we also experimentally study the PMA dependence on the minimum size of skyrmions. Although field-driven skyrmion generation is unsuitable for device application, this result can provide an easier approach for obtaining isolated skyrmions, making skyrmion-based research more accessible.
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Affiliation(s)
- Seungmo Yang
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
| | - Tae-Seong Ju
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
- Department
of Physics, Pusan National University, Busan46241, Republic of Korea
| | - Changsoo Kim
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
| | - Hyun-Joong Kim
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
| | - Kyongmo An
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
| | - Kyoung-Woong Moon
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
| | - Sungkyun Park
- Department
of Physics, Pusan National University, Busan46241, Republic of Korea
| | - Chanyong Hwang
- Quantum
Spin Team, Korea Research Institute of Standards
and Science, Daejeon34113, Republic of Korea
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3
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Krupinski M, Sobieszczyk P, Zieliński P, Marszałek M. Magnetic reversal in perpendicularly magnetized antidot arrays with intrinsic and extrinsic defects. Sci Rep 2019; 9:13276. [PMID: 31527641 PMCID: PMC6746764 DOI: 10.1038/s41598-019-49869-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 08/31/2019] [Indexed: 11/30/2022] Open
Abstract
Defects can significantly affect performance of nanopatterned magnetic devices, therefore their influence on the material properties has to be understood well before the material is used in technological applications. However, this is experimentally challenging due to the inability of the control of defect characteristics in a reproducible manner. Here, we construct a micromagnetic model, which accounts for intrinsic and extrinsic defects associated with the polycrystalline nature of the material and with corrugated edges of nanostructures. The predictions of the model are corroborated by the measurements obtained for highly ordered arrays of circular Co/Pd antidots with perpendicular magnetic anisotropy. We found that magnetic properties, magnetic reversal and the evolution of the domain pattern are strongly determined by density of defects, heterogeneity of nanostructures, and edge corrugations. In particular, an increase in the Néel domain walls, as compared to Bloch walls, was observed with a increase of the antidot diameters, suggesting that a neck between two antidots can behave like a nanowire with a width determined by the array period and antidot size. Furthermore, the presence of edge corrugations can lead to the formation of a network of magnetic bubbles, which are unstable in non-patterned flat films.
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Affiliation(s)
- Michal Krupinski
- Institute of Nuclear Physics Polish Academy of Sciences, Radzikowskiego 152, 31-342, Kraków, Poland.
| | - Pawel Sobieszczyk
- Institute of Nuclear Physics Polish Academy of Sciences, Radzikowskiego 152, 31-342, Kraków, Poland
| | - Piotr Zieliński
- Institute of Nuclear Physics Polish Academy of Sciences, Radzikowskiego 152, 31-342, Kraków, Poland
| | - Marta Marszałek
- Institute of Nuclear Physics Polish Academy of Sciences, Radzikowskiego 152, 31-342, Kraków, Poland
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4
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Cannas SA, Stariolo DA. Three-state model with competing antiferromagnetic and pairing interactions. Phys Rev E 2019; 99:042137. [PMID: 31108696 DOI: 10.1103/physreve.99.042137] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Indexed: 11/07/2022]
Abstract
Motivated by the rich phase diagram of the high-temperature superconductors, we introduce a pseudospin model with three state variables which can be interpreted as two states (spin ±1/2) particles and holes. The Hamiltonian has a term which favors antiferromagnetism and an additional competing interaction which favors bonding between pairs of antiparallel spins mediated by holes. For low concentration of holes the dominant interaction between particles has antiferromagnetic character, leading to an antiferromagnetic phase in the temperature-hole concentration phase diagram, qualitatively similar to the antiferromagnetic phase of doped Mott insulators. For growing concentration of holes antiferromagnetic order is weakened and a phase with a different kind of order mediated by holes appears. This last phase has the form of a dome in the T-hole concentration plane. The whole phase diagram resembles those of some families of high-T_{c} superconductors. We compute the phase diagram in the mean-field approximation and characterize the different phase transitions through Monte Carlo simulations.
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Affiliation(s)
- Sergio A Cannas
- Facultad de Matemática, Astronomía, Física y Computación, Universidad Nacional de Córdoba, Instituto de Física Enrique Gaviola (IFEG-CONICET) Ciudad Universitaria, 5000 Córdoba, Argentina
| | - Daniel A Stariolo
- Departamento de Física, Universidade Federal Fluminense and National Institute of Science and Technology for Complex Systems Av. Gal. Milton Tavares de Souza s/n, Campus Praia Vermelha, 24210-346 Niterói, RJ, Brazil
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5
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Mendoza-Coto A, Nicolao L, Díaz-Méndez R. On the mechanism behind the inverse melting in systems with competing interactions. Sci Rep 2019; 9:2020. [PMID: 30765837 PMCID: PMC6375973 DOI: 10.1038/s41598-018-38465-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Accepted: 12/27/2018] [Indexed: 11/09/2022] Open
Abstract
The competition between a short range attractive interaction and a nonlocal repulsive interaction promote the appearance of modulated phases. In this work we present the microscopic mechanisms leading to the emergence of inverse transitions in such systems by considering a thorough mean-field analysis of a variety of minimal models with different competing interactions. We identify the specific connections between the characteristic energy of the homogeneous and modulated phases and the observed reentrant behaviors in the phase diagram. In particular, we find that reentrance is appreciable when the characteristic energy cost of the homogeneous and modulated phases are comparable to each other, and for systems in which the local order parameter is limited. In the asymptotic limit of high energy cost of the homogeneous phase we observe that the degree of reentrance decreases exponentially with the ratio of the characteristic energy cost of homogeneous and modulated phases. These mean-field results are confronted with Langevin simulations of an effective coarse grained model, confirming the expected extension of the reentrance in the phase diagram. These results shed new light on many systems undergoing inverse melting transitions by qualitatively improving the understanding of the interplay of entropy and energy around the inverse melting points.
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Affiliation(s)
- Alejandro Mendoza-Coto
- Departamento de Física, Universidade Federal de Santa Catarina, 88040-900, Florianópolis, Brazil.
| | - Lucas Nicolao
- Departamento de Física, Universidade Federal de Santa Catarina, 88040-900, Florianópolis, Brazil
| | - Rogelio Díaz-Méndez
- Department of Theoretical Physics, KTH Royal Institute of Technology, SE-106 91, Stockholm, Sweden
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6
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Fin S, Silvani R, Tacchi S, Marangolo M, Garnier LC, Eddrief M, Hepburn C, Fortuna F, Rettori A, Pini MG, Bisero D. Straight motion of half-integer topological defects in thin Fe-N magnetic films with stripe domains. Sci Rep 2018; 8:9339. [PMID: 29921938 PMCID: PMC6008308 DOI: 10.1038/s41598-018-27283-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Accepted: 05/31/2018] [Indexed: 11/09/2022] Open
Abstract
In thin magnetic films with perpendicular magnetic anisotropy, a periodic “up-down” stripe-domain structure can be originated at remanence, on a mesoscopic scale (~100 nm) comparable with film thickness, by the competition between short-range exchange coupling and long-range dipolar interaction. However, translational order is perturbed because magnetic edge dislocations are spontaneously nucleated. Such topological defects play an important role in magnetic films since they promote the in-plane magnetization reversal of stripes and, in superconductor/ferromagnet hybrids, the creation of superconducting vortex clusters. Combining magnetic force microscopy experiments and micromagnetic simulations, we investigated the motion of two classes of magnetic edge dislocations, randomly distributed in an \documentclass[12pt]{minimal}
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\begin{document}$${{\rm{N}}}_{2}^{+}$$\end{document}N2+-implanted Fe film. They were found to move in opposite directions along straight trajectories parallel to the stripes axis, when driven by a moderate dc magnetic field. Using the approximate Thiele equation, analytical expressions for the forces acting on such magnetic defects and a microscopic explanation for the direction of their motion could be obtained. Straight trajectories are related to the presence of a periodic stripe domain pattern, which imposes the gyrotropic force to vanish even if a nonzero, half-integer topological charge is carried by the defects in some layers across the film thickness.
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Affiliation(s)
- S Fin
- Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara, Via Saragat 1, I-44122, Ferrara, Italy
| | - R Silvani
- Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Via Pascoli, I-06123, Perugia, Italy
| | - S Tacchi
- Istituto Officina dei Materiali del CNR (CNR-IOM), Sede Secondaria di Perugia, c/o Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, I-06123, Perugia, Italy
| | - M Marangolo
- Sorbonne Université, CNRS, Institut des NanoSciences de Paris, UMR 7588, F-75252, Paris, France
| | - L-C Garnier
- Sorbonne Université, CNRS, Institut des NanoSciences de Paris, UMR 7588, F-75252, Paris, France.,Université Versailles St-Quentin, LISV, Bâtiment Boucher, Pôle scientifique et technologique de Vélizy, 10-12 avenue de l'Europe, F-78140, Vélizy, France
| | - M Eddrief
- Sorbonne Université, CNRS, Institut des NanoSciences de Paris, UMR 7588, F-75252, Paris, France
| | - C Hepburn
- Sorbonne Université, CNRS, Institut des NanoSciences de Paris, UMR 7588, F-75252, Paris, France
| | - F Fortuna
- CSNSM, Université Paris-Sud and CNRS/IN2P3, Université Paris-Saclay, F-91405, Orsay, France
| | - A Rettori
- Dipartimento di Fisica ed Astronomia, Università degli Studi di Firenze, Via Sansone 1, I-50019, Sesto Fiorentino, FI, Italy
| | - M G Pini
- Istituto dei Sistemi Complessi del CNR (CNR-ISC), Sede Secondaria di Sesto Fiorentino, Via Madonna del Piano 10, I-50019, Sesto Fiorentino, FI, Italy.
| | - D Bisero
- Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara, Via Saragat 1, I-44122, Ferrara, Italy. .,CNISM, Unità di Ferrara, I-44122, Ferrara, Italy.
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7
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Pȩkalski J, Ciach A. Orientational ordering of lamellar structures on closed surfaces. J Chem Phys 2018; 148:174902. [PMID: 29739225 DOI: 10.1063/1.5026112] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Self-assembly of particles with short-range attraction and long-range repulsion interactions on a flat and on a spherical surface is compared. Molecular dynamics simulations are performed for the two systems having the same area and the density optimal for formation of stripes of particles. Structural characteristics, e.g., a cluster size distribution, a number of defects, and an orientational order parameter (OP), as well as the specific heat, are obtained for a range of temperatures. In both cases, the cluster size distribution becomes bimodal and elongated clusters appear at the temperature corresponding to the maximum of the specific heat. When the temperature decreases, orientational ordering of the stripes takes place and the number of particles per cluster or stripe increases in both cases. However, only on the flat surface, the specific heat has another maximum at the temperature corresponding to a rapid change of the OP. On the sphere, the crossover between the isotropic and anisotropic structures occur in a much broader temperature interval; the orientational order is weaker and occurs at significantly lower temperature. At low temperature, the stripes on the sphere form spirals and the defects resemble defects in the nematic phase of rods adsorbed at a sphere.
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Affiliation(s)
- J Pȩkalski
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland
| | - A Ciach
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland
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8
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Ludbrook BM, Dubuis G, Puichaud AH, Ruck BJ, Granville S. Nucleation and annihilation of skyrmions in Mn 2CoAl observed through the topological Hall effect. Sci Rep 2017; 7:13620. [PMID: 29051573 PMCID: PMC5648899 DOI: 10.1038/s41598-017-13211-8] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Accepted: 09/21/2017] [Indexed: 11/20/2022] Open
Abstract
Magnetic skyrmions are topologically protected spin textures with great technological potential. These topologically non-trivial non-coplanar spin textures give rise to a topological Hall effect, enabling the purely electronic detection of magnetic skyrmions. We report a clear topological Hall effect in thin films of the the Heusler alloy Mn2CoAl, a ferromagnetic spin-gapless semiconductor, capped by a thin layer of Pd. We exploit the strong thickness- and temperature-dependence of the anomalous Hall effect in this system, tuning it to zero to enable the unambiguous measurement of the topological Hall effect, which is observed for temperatures between 3 K and 280 K. The topological Hall effect is evidence of skyrmions, and we demonstrate the simultaneous coexistence of opposite polarity skyrmions using a novel method involving minor field loops of the Hall effect.
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Affiliation(s)
- B M Ludbrook
- The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, 6140, New Zealand
| | - G Dubuis
- The MacDiarmid Institute for Advanced Materials and Nanotechnology, Robinson Research Institute, Victoria University of Wellington, P.O. Box 33436, Lower Hutt, 5046, New Zealand
| | - A-H Puichaud
- The MacDiarmid Institute for Advanced Materials and Nanotechnology, Robinson Research Institute, Victoria University of Wellington, P.O. Box 33436, Lower Hutt, 5046, New Zealand
| | - B J Ruck
- The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, 6140, New Zealand
| | - S Granville
- The MacDiarmid Institute for Advanced Materials and Nanotechnology, Robinson Research Institute, Victoria University of Wellington, P.O. Box 33436, Lower Hutt, 5046, New Zealand.
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9
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Critical exponents and scaling invariance in the absence of a critical point. Nat Commun 2016; 7:13611. [PMID: 27917865 PMCID: PMC5150222 DOI: 10.1038/ncomms13611] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Accepted: 10/18/2016] [Indexed: 11/08/2022] Open
Abstract
The paramagnetic-to-ferromagnetic phase transition is classified as a critical phenomenon due to the power-law behaviour shown by thermodynamic observables when the Curie point is approached. Here we report the observation of such a behaviour over extraordinarily many decades of suitable scaling variables in ultrathin Fe films, for certain ranges of temperature T and applied field B. This despite the fact that the underlying critical point is practically unreachable because protected by a phase with a modulated domain structure, induced by the dipole–dipole interaction. The modulated structure has a well-defined spatial period and is realized in a portion of the (T, B) plane that extends above the putative critical temperature, where thermodynamic quantities do not display any singularity. Our results imply that scaling behaviour of macroscopic observables is compatible with an avoided critical point. Thermodynamic observables develop power laws and singularities when approaching the Curie point of a ferromagnetic phase transition. Here, Saratz et al. demonstrate that topological excitations (that is, magnetic domains in Fe/Cu(100) films that even persist above the Curie point) remove those singularities compatibly with an avoided critical point.
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10
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Martínez MDP, Milano J, Eddrief M, Marangolo M, Bustingorry S. Modeling magnetization curves in magnetic thin films with striped patterns. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:136001. [PMID: 26941191 DOI: 10.1088/0953-8984/28/13/136001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
In this work, we study magnetic thin films presenting magnetic stripe patterns. A fingerprint of such domains is a linear behavior of the in-plane magnetization curves below a given saturation field. We present free energy models for the in-plane magnetization curves which permit us to extract key geometrical information about the stripe patterns, such as the maximum canted angle of the magnetization and the domain wall width. As an example, we discuss in this work magnetization curves for Fe(1-x)Ga(x) magnetic films which present a stripe pattern with a period of 160 nm and we found a typical maximum canted angle of 85° and a domain wall width around 30 nm.
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Affiliation(s)
- M Di Pietro Martínez
- Instituto Balseiro, Universidad Nacional de Cuyo, Av. Bustillo 9500, (R8402AGP) San Carlos de Bariloche, RN, Argentina
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11
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Yu G, Upadhyaya P, Li X, Li W, Kim SK, Fan Y, Wong KL, Tserkovnyak Y, Amiri PK, Wang KL. Room-Temperature Creation and Spin-Orbit Torque Manipulation of Skyrmions in Thin Films with Engineered Asymmetry. NANO LETTERS 2016; 16:1981-1988. [PMID: 26848783 DOI: 10.1021/acs.nanolett.5b05257] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Magnetic skyrmions, which are topologically protected spin textures, are promising candidates for ultralow-energy and ultrahigh-density magnetic data storage and computing applications. To date, most experiments on skyrmions have been carried out at low temperatures. The choice of available materials is limited, and there is a lack of electrical means to control skyrmions in devices. In this work, we demonstrate a new method for creating a stable skyrmion bubble phase in the CoFeB-MgO material system at room temperature, by engineering the interfacial perpendicular magnetic anisotropy of the ferromagnetic layer. Importantly, we also demonstrate that artificially engineered symmetry breaking gives rise to a force acting on the skyrmions, in addition to the current-induced spin-orbit torque, which can be used to drive their motion. This room-temperature creation and manipulation of skyrmions offers new possibilities to engineer skyrmionic devices. The results bring skyrmionic memory and logic concepts closer to realization in industrially relevant and manufacturable thin film material systems.
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Affiliation(s)
- Guoqiang Yu
- Department of Electrical Engineering, University of California , Los Angeles, California 90095, United States
| | - Pramey Upadhyaya
- Department of Electrical Engineering, University of California , Los Angeles, California 90095, United States
| | - Xiang Li
- Department of Electrical Engineering, University of California , Los Angeles, California 90095, United States
| | - Wenyuan Li
- Department of Electrical Engineering, University of California , Los Angeles, California 90095, United States
| | - Se Kwon Kim
- Department of Physics and Astronomy, University of California , Los Angeles, California 90095, United States
| | - Yabin Fan
- Department of Electrical Engineering, University of California , Los Angeles, California 90095, United States
| | - Kin L Wong
- Department of Electrical Engineering, University of California , Los Angeles, California 90095, United States
| | - Yaroslav Tserkovnyak
- Department of Physics and Astronomy, University of California , Los Angeles, California 90095, United States
| | - Pedram Khalili Amiri
- Department of Electrical Engineering, University of California , Los Angeles, California 90095, United States
| | - Kang L Wang
- Department of Electrical Engineering, University of California , Los Angeles, California 90095, United States
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12
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Guerrero AI, Stariolo DA, Almarza NG. Nematic phase in the J(1)-J(2) square-lattice Ising model in an external field. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 91:052123. [PMID: 26066135 DOI: 10.1103/physreve.91.052123] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2015] [Indexed: 06/04/2023]
Abstract
The J(1)-J(2) Ising model in the square lattice in the presence of an external field is studied by two approaches: the cluster variation method (CVM) and Monte Carlo simulations. The use of the CVM in the square approximation leads to the presence of a new equilibrium phase, not previously reported for this model: an Ising-nematic phase, which shows orientational order but not positional order, between the known stripes and disordered phases. Suitable order parameters are defined, and the phase diagram of the model is obtained. Monte Carlo simulations are in qualitative agreement with the CVM results, giving support to the presence of the new Ising-nematic phase. Phase diagrams in the temperature-external field plane are obtained for selected values of the parameter κ=J(2)/|J(1)| which measures the relative strength of the competing interactions. From the CVM in the square approximation we obtain a line of second order transitions between the disordered and nematic phases, while the nematic-stripes phase transitions are found to be of first order. The Monte Carlo results suggest a line of second order nematic-disordered phase transitions in agreement with the CVM results. Regarding the stripes-nematic transitions, the present Monte Carlo results are not precise enough to reach definite conclusions about the nature of the transitions.
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Affiliation(s)
- Alejandra I Guerrero
- Departamento de Física, Universidade Federal do Rio Grande do Sul CP 15051, 91501-970 Porto Alegre, RS, Brazil
| | - Daniel A Stariolo
- Departamento de Física, Universidade Federal do Rio Grande do Sul and National Institute of Science and Technology for Complex Systems, CP 15051, 91501-970 Porto Alegre, RS, Brazil
| | - Noé G Almarza
- Instituto de Química Física Rocasolano, CSIC, Serrano 119, E-28006 Madrid, Spain
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13
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Real-time observation of domain fluctuations in a two-dimensional magnetic model system. Nat Commun 2015; 6:6832. [PMID: 25902073 PMCID: PMC4423231 DOI: 10.1038/ncomms7832] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Accepted: 03/04/2015] [Indexed: 11/08/2022] Open
Abstract
Domain patterns of perpendicularly magnetized ultra-thin ferromagnetic films are often determined by the competition of the short range but strong exchange interaction favouring ferromagnetic alignment of magnetic moments and the long range but weak antiferromagnetic dipolar interaction. Detailed phase diagrams of the resulting stripe domain patterns have been evaluated in recent years; however, the domain fluctuations in these pattern forming systems have not been studied in great detail so far. Here we show that domain fluctuations can be observed in ultra-thin two-dimensional ferromagnetic Fe/Ni/Cu(001) films with perpendicular magnetization in the stripe domain phase. Non-stroboscopic time-resolved threshold photoemission electron microscopy with high temporal resolution allows analysing the dynamic fingerprint of the topological excitations in the nematic domain phase. Furthermore, proliferation of domain ending defects in the vicinity of the spin reorientation transition is witnessed.
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14
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Barci DG, Mendoza-Coto A, Stariolo DA. Nematic phase in stripe-forming systems within the self-consistent screening approximation. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:062140. [PMID: 24483418 DOI: 10.1103/physreve.88.062140] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2013] [Indexed: 06/03/2023]
Abstract
We show that in order to describe the isotropic-nematic transition in stripe-forming systems with isotropic competing interactions of the Brazovskii class it is necessary to consider the next to leading order in a 1/N approximation for the effective Hamiltonian. This can be conveniently accomplished within the self-consistent screening approximation. We solve the relevant equations and show that the self-energy in this approximation is able to generate the essential wave vector dependence to account for the anisotropic character of a two-point correlation function characteristic of a nematic phase.
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Affiliation(s)
- Daniel G Barci
- Departamento de Física Teórica, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, 20550-013 Rio de Janeiro, Brazil
| | - Alejandro Mendoza-Coto
- Departamento de Física, Universidade Federal do Rio Grande do Sul, CP 15051, 91501-970 Porto Alegre, RS, Brazil
| | - Daniel A Stariolo
- Departamento de Física, Universidade Federal do Rio Grande do Sul, CP 15051, 91501-970 Porto Alegre, RS, Brazil
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15
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Dipolar-energy-activated magnetic domain pattern transformation driven by thermal fluctuations. Nat Commun 2013; 4:2054. [PMID: 23784257 DOI: 10.1038/ncomms3054] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2012] [Accepted: 05/24/2013] [Indexed: 11/08/2022] Open
Abstract
Two-dimensional ferromagnetic layers can serve as a playground for the study of basic physical properties of various pattern forming systems by virtue of their tuneable magnetic properties. Here we use threshold photoemission magnetic circular dichroism in combination with photoemission electron microscopy to investigate ultra-thin ferromagnetic Fe/Ni/Cu(001) films in the stripe domain phase near the spin reorientation transition as a function of film thickness, temperature and effective anisotropy. Here we report a metastable domain state with domain width larger than the thermodynamically stable one as a result of a rapid reduction of the anisotropy. The transformation into the equilibrium state takes place via the propagation of a transition front, which originates from defined steps in the film thickness.
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Barci DG, Ribeiro L, Stariolo DA. Nematic phase in two-dimensional frustrated systems with power-law decaying interactions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 87:062119. [PMID: 23848639 DOI: 10.1103/physreve.87.062119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2013] [Indexed: 06/02/2023]
Abstract
We address the problem of orientational order in frustrated interaction systems as a function of the relative range of the competing interactions. We study a spin model Hamiltonian with short-range ferromagnetic interaction competing with an antiferromagnetic component that decays as a power law of the distance between spins, 1/r(α). These systems may develop a nematic phase between the isotropic disordered and stripe phases. We evaluate the nematic order parameter using a self-consistent mean-field calculation. Our main result indicates that the nematic phase exists, at mean-field level, provided 0<α<4. We analytically compute the nematic critical temperature and show that it increases with the range of the interaction, reaching its maximum near α~0.5. We also compute a coarse-grained effective Hamiltonian for long wavelength fluctuations. For 0<α<4 the inverse susceptibility develops a set of continuous minima at wave vectors |k[over arrow]|=k(0)(α) which dictate the long-distance physics of the system. For α→4, k(0)→0, making the competition between interactions ineffective for greater values of α.
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Affiliation(s)
- Daniel G Barci
- Departamento de Física Teórica, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, 20550-013 Rio de Janeiro, Brazil
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Mendoza-Coto A, Stariolo DA. Coarse-grained models of stripe forming systems: phase diagrams, anomalies, and scaling hypothesis. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 86:051130. [PMID: 23214761 DOI: 10.1103/physreve.86.051130] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2012] [Indexed: 06/01/2023]
Abstract
Two coarse-grained models which capture some universal characteristics of stripe forming systems are studied. At high temperatures, the structure factors of both models attain their maxima on a circle in reciprocal space, as a consequence of generic isotropic competing interactions. Although this is known to lead to some universal properties, we show that the phase diagrams have important differences, which are a consequence of the particular k dependence of the fluctuation spectrum in each model. The phase diagrams are computed in a mean field approximation and also after inclusion of small fluctuations, which are shown to modify drastically the mean field behavior. Observables like the modulation length and magnetization profiles are computed for the whole temperature range accessible to both models and some important differences in behavior are observed. A stripe compression modulus is computed, showing an anomalous behavior with temperature as recently reported in related models. Also, a recently proposed scaling hypothesis for modulated systems is tested and found to be valid for both models studied.
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Affiliation(s)
- Alejandro Mendoza-Coto
- Departamento de Física, Universidade Federal do Rio Grande do Sul, CP 15051, 91501-970 Porto Alegre, Brazil
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Pighin SA, Billoni OV, Cannas SA. Finite-temperature phase diagram of ultrathin magnetic films without external fields. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 86:051119. [PMID: 23214750 DOI: 10.1103/physreve.86.051119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2012] [Revised: 10/15/2012] [Indexed: 06/01/2023]
Abstract
We analyze the finite-temperature phase diagram of ultrathin magnetic films by introducing a mean-field theory, valid in the low-anisotropy regime, i.e., close to the spin reorientation transition. The theoretical results are compared with Monte Carlo simulations carried out on a microscopic Heisenberg model. Connections between the finite-temperature behavior and the ground-state properties of the system are established. Several properties of the stripe pattern, such as the presence of canted states, the stripe width variation phenomenon, and the associated magnetization profiles, are also analyzed.
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Affiliation(s)
- Santiago A Pighin
- Centro Atómico Bariloche, Comisión Nacional de Energía Atómica, CNEA, CONICET, Avenida E Bustillo 9500, R8402AGP SC de Bariloche, Argentina.
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Hierro-Rodriguez A, Cid R, Vélez M, Rodriguez-Rodriguez G, Martín JI, Álvarez-Prado LM, Alameda JM. Topological defects and misfit strain in magnetic stripe domains of lateral multilayers with perpendicular magnetic anisotropy. PHYSICAL REVIEW LETTERS 2012; 109:117202. [PMID: 23005668 DOI: 10.1103/physrevlett.109.117202] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2012] [Indexed: 05/26/2023]
Abstract
Stripe domains are studied in perpendicular magnetic anisotropy films nanostructured with a periodic thickness modulation that induces the lateral modulation of both stripe periods and in-plane magnetization. The resulting system is the 2D equivalent of a strained superlattice with properties controlled by interfacial misfit strain within the magnetic stripe structure and shape anisotropy. This allows us to observe, experimentally for the first time, the continuous structural transformation of a grain boundary in this 2D magnetic crystal in the whole angular range. The magnetization reversal process can be tailored through the effect of misfit strain due to the coupling between disclinations in the magnetic stripe pattern and domain walls in the in-plane magnetization configuration.
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