The design and verification of Mumax3
TL;DR: In this paper, the authors report on the design, verification and performance of mumax3, an open-source GPU-accelerated micromagnetic simulation program that solves the time and space dependent magnetization evolution in nano-to micro-scale magnets using a finite-difference discretization.
Abstract: We report on the design, verification and performance of mumax3, an open-source GPU-accelerated micromagnetic simulation program. This software solves the time- and space dependent magnetization evolution in nano- to micro scale magnets using a finite-difference discretization. Its high performance and low memory requirements allow for large-scale simulations to be performed in limited time and on inexpensive hardware. We verified each part of the software by comparing results to analytical values where available and to micromagnetic standard problems. mumax3 also offers specific extensions like MFM image generation, moving simulation window, edge charge removal and material grains.
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TL;DR: This work designed cobalt-based multilayered thin thin metals in which the cobalt layer is sandwiched between two heavy metals and so provides additive interfacial Dzyaloshinskii-Moriya interactions (DMIs), which reach a value close to 2 mJ m(-2) in the case of the Ir|Co|Pt asymmetric multilayers.
Abstract: Facing the ever-growing demand for data storage will most probably require a new paradigm. Nanoscale magnetic skyrmions are anticipated to solve this issue as they are arguably the smallest spin textures in magnetic thin films in nature. We designed cobalt-based multilayered thin films in which the cobalt layer is sandwiched between two heavy metals and so provides additive interfacial Dzyaloshinskii-Moriya interactions (DMIs), which reach a value close to 2 mJ m(-2) in the case of the Ir|Co|Pt asymmetric multilayers. Using a magnetization-sensitive scanning X-ray transmission microscopy technique, we imaged small magnetic domains at very low fields in these multilayers. The study of their behaviour in a perpendicular magnetic field allows us to conclude that they are actually magnetic skyrmions stabilized by the large DMI. This discovery of stable sub-100 nm individual skyrmions at room temperature in a technologically relevant material opens the way for device applications in the near future.
1,023 citations
University of California, Berkeley1, Argonne National Laboratory2, University of California, Los Angeles3, Massachusetts Institute of Technology4, University of California, San Diego5, University of Minnesota6, University of Texas at Austin7, Cornell University8, University of South Florida9, Stanford University10, University of California, Santa Cruz11, Ohio State University12, Academy of Sciences of the Czech Republic13, University of Nottingham14, Radboud University Nijmegen15, Eindhoven University of Technology16, University of California, Irvine17, Drexel University18, Northwestern University19, Pennsylvania State University20, Oakland University21, National Institute of Standards and Technology22, Johns Hopkins University23, University of Denver24
TL;DR: This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces, identifying the most exciting new scientific results and pointing to promising future research directions.
Abstract: This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin transfer torque, and spin pumping. An overview is provided to the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. The article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes.
758 citations
TL;DR: This work presents a tunable RT skyrmion platform based on multilayer stacks of Ir/Fe/Co/Pt, which is established a platform for investigating functional sub-50-nm RTskyrmions, pointing towards the development of skyrMion-based memory devices.
Abstract: Magnetic skyrmions are nanoscale topological spin structures offering great promise for next-generation information storage technologies. The recent discovery of sub-100-nm room-temperature (RT) skyrmions in several multilayer films has triggered vigorous efforts to modulate their physical properties for their use in devices. Here we present a tunable RT skyrmion platform based on multilayer stacks of Ir/Fe/Co/Pt, which we study using X-ray microscopy, magnetic force microscopy and Hall transport techniques. By varying the ferromagnetic layer composition, we can tailor the magnetic interactions governing skyrmion properties, thereby tuning their thermodynamic stability parameter by an order of magnitude. The skyrmions exhibit a smooth crossover between isolated (metastable) and disordered lattice configurations across samples, while their size and density can be tuned by factors of two and ten, respectively. We thus establish a platform for investigating functional sub-50-nm RT skyrmions, pointing towards the development of skyrmion-based memory devices.
641 citations
TL;DR: This study demonstrates a method leading to the formation of magnetic skyrmions in a micrometer-sized track using homogeneous current injection and addresses the particularly important role of the magnetic inhomogeneities on the current-induced motion of sub-100 nm skyrMions for which the material grains size is comparable to theskyrmion diameter.
Abstract: Magnetic skyrmions are nanoscale windings of the spin configuration that hold great promise for technology due to their topology-related properties and extremely reduced sizes. After the recent observation at room temperature of sub-100 nm skyrmions stabilized by interfacial chiral interaction in magnetic multilayers, several pending questions remain to be solved, notably about the means to nucleate individual compact skyrmions or the exact nature of their motion. In this study, a method leading to the formation of magnetic skyrmions in a micrometer-sized track using homogeneous current injection is evidenced. Spin-transfer-induced motion of these small electrical-current-generated skyrmions is then demonstrated and the role of the out-of-plane magnetic field in the stabilization of the moving skyrmions is also analyzed. The results of these experimental observations of spin torque induced motion are compared to micromagnetic simulations reproducing a granular type, nonuniform magnetic multilayer in order...
371 citations
TL;DR: It is demonstrated that room-temperature antiferromagnetic skyrmions can be stabilized in synthetic antiferromaagnets (SAFs), in which perpendicular magnetic anisotropy, antiferromeagnetic coupling and chiral order can be adjusted concurrently.
Abstract: Room-temperature skyrmions in ferromagnetic films and multilayers show promise for encoding information bits in new computing technologies. Despite recent progress, ferromagnetic order generates dipolar fields that prevent ultrasmall skyrmion sizes, and allows a transverse deflection of moving skyrmions that hinders their efficient manipulation. Antiferromagnetic skyrmions shall lift these limitations. Here we demonstrate that room-temperature antiferromagnetic skyrmions can be stabilized in synthetic antiferromagnets (SAFs), in which perpendicular magnetic anisotropy, antiferromagnetic coupling and chiral order can be adjusted concurrently. Utilizing interlayer electronic coupling to an adjacent bias layer, we demonstrate that spin-spiral states obtained in a SAF with vanishing perpendicular magnetic anisotropy can be turned into isolated antiferromagnetic skyrmions. We also provide model-based estimates of skyrmion size and stability, showing that room-temperature antiferromagnetic skyrmions below 10 nm in radius can be anticipated in further optimized SAFs. Antiferromagnetic skyrmions in SAFs may thus solve major issues associated with ferromagnetic skyrmions for low-power spintronic devices.
326 citations
References
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IBM1
TL;DR: In this paper, a new mechanism was proposed for exciting the magnetic state of a ferromagnet, where a transfer of vectorial spin accompanied an electric current flowing perpendicular to two parallel magnetic films connected by a normal metallic spacer.
5,824 citations
Journal Article•
2,543 citations
01 Jan 1935
TL;DR: This chapter examines the distribution of magnetic moments in a ferromagnetic crystal and finds that if the crystal is placed in an external magnetic field, the boundaries between the layers begin to move so that the layers with magnetic moments parallel to the field become wider.
Abstract: Publisher Summary This chapter examines the distribution of magnetic moments in a ferromagnetic crystal. When the crystal is magnetized, the boundaries between the oppositely magnetized layers move so that the layers with one direction of magnetic moment grow at the cost of the layers with moments in the opposite direction. The presence of separate elementary regions, magnetized in opposite directions, is due only to the demagnetizing effect of the surface, and the number and dimensions of these regions are entirely determined by the dimensions of the body. The analysis of the preceding section gives only the distribution of the directions of the magnetic moments in the intermediate regions but gives nothing for determining the width of the layers. If the crystal is placed in an external magnetic field, which is directed parallel to the axis of easiest magnetization, the boundaries between the layers begin to move so that the layers with magnetic moments parallel to the field become wider.
1,866 citations
TL;DR: This work compute the response of the conduction electron spins in a spatial and time varying magnetization M(r,t) in the time-dependent semiclassical transport theory and shows that the induced nonequilibrium conduction spin density generates four spin torques acting on the magnetization.
Abstract: The mutual dependence of spin-dependent conduction and magnetization dynamics of ferromagnets provides the key mechanisms in various spin-dependent phenomena. We compute the response of the conduction electron spins in a spatial and time varying magnetization M(r,t) in the time-dependent semiclassical transport theory. We show that the induced nonequilibrium conduction spin density in turn generates four spin torques acting on the magnetization-with each torque playing a different role in magnetization dynamics. By comparing with recent theoretical models, we find that one of these torques which has not been previously identified is crucial to consistently interpreting experimental data on domain wall motion.
1,125 citations