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Micromagnetic modelling—the current state of the art
Josef Fidler,Thomas Schrefl +1 more
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In this article, a dynamic micromagnetic code based on the Gilbert equation of motion to study the time evolution of the magnetization has been developed, and three different regimes have been identified.Abstract:
The increasing information density in magnetic recording, the miniaturization in magnetic sensor technology, the trend towards nanocrystalline magnetic materials and the improved availability of large-scale computer power are the main reasons why micromagnetic modelling has been developing extremely rapidly. Computational micromagnetism leads to a deeper understanding of hysteresis effects by visualization of the magnetization reversal process. Recent advances in numerical simulation techniques are reviewed. Higher order finite elements and adaptive meshing have been introduced, in order to reduce the discretization error. The use of a hybrid boundary/finite element method enables accurate stray field computation for arbitrary shaped particles and takes into account the granular microstructure of the material. A dynamic micromagnetic code based on the Gilbert equation of motion to study the time evolution of the magnetization has been developed. Finite element models for different materials and magnet shapes are obtained from a Voronoi construction and subsequent meshing of the polyhedral regions. Adaptive refinement and coarsening of the finite element mesh guarantees accurate solutions near magnetic inhomogeneities or domain walls, while keeping the number of elements small. The polycrystalline microstructure and assumed random magnetocrystalline anisotropy of elongated Co elements decreases the coercive field and the switching time compared to zero anisotropy elements, in which vortices form and move only after a certain waiting time after the application of a reversed field close to the coercive field. NiFe elements with flat, rounded and slanted ends show different hysteresis properties and switching dynamics. Micromagnetic simulations show that the magnetic properties of intergranular regions in nucleation-controlled Nd-Fe-B hard magnetic materials control the coercive field. Exchange interactions between neighbouring soft and hard grains lead to remanence enhancement of isotropically oriented grains in nanocrystalline composite magnets. Upper limits of the coercive field of pinning-controlled Sm-Co magnets for high-temperature applications are predicted from the micromagnetic calculations. Incorporating thermally activated magnetization reversal and micromagnetics we found complex magnetization reversal mechanisms for small spherical magnetic particles. The magnetocrystalline anisotropy and the external field strength determine the switching mechanism. Three different regimes have been identified. For fields, which are smaller than the anisotropy field, magnetization by coherent switching has been observed. Single droplet nucleation occurs, if the external field is comparable to the anisotropy field, and multi-droplet nucleation is the driving reversal process for higher fields.read more
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Spin transfer torques
Daniel C. Ralph,Mark D. Stiles +1 more
TL;DR: In this paper, the physics of spin transfer torque in magnetic devices are discussed and an elementary discussion of the mechanism and experimental progress in this field is provided, along with a review of theoretical and experimental results.
Journal ArticleDOI
Ultrafast optical manipulation of magnetic order
TL;DR: In this article, the authors review the progress in this field of laser manipulation of magnetic order in a systematic way and show that the polarization of light plays an essential role in the manipulation of the magnetic moments at the femtosecond time scale.
Journal ArticleDOI
Nanofabricated and self-assembled magnetic structures as data storage media
Bruce D. Terris,T. Thomson +1 more
TL;DR: Nanofabrication of magnetic storage media, where servo marks, discrete tracks or individual islands are defined, offers the prospect for improved performance and increased areal density as discussed by the authors.
Journal ArticleDOI
Interface-induced phenomena in magnetism
Frances Hellman,Axel Hoffmann,Yaroslav Tserkovnyak,Geoffrey S. D. Beach,Eric E. Fullerton,Chris Leighton,Allan H. MacDonald,Daniel C. Ralph,Dario Arena,Hermann A. Dürr,Peter Fischer,Julie Grollier,Joseph P. Heremans,Tomas Jungwirth,Tomas Jungwirth,Alexey Kimel,B Bert Koopmans,Ilya Krivorotov,Steven J. May,Amanda K. Petford-Long,James M. Rondinelli,Nitin Samarth,Ivan K. Schuller,Ivan K. Schuller,Andrei Slavin,Mark D. Stiles,Oleg Tchernyshyov,André Thiaville,Barry L. Zink +28 more
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.
Journal ArticleDOI
Magnetic recording: advancing into the future
Andreas Moser,Kentaro Takano,David Thomas Margulies,Manfred Albrecht,Yoshiaki Sonobe,Yoshihiro Ikeda,Shouheng Sun,Eric E. Fullerton +7 more
TL;DR: In this article, the authors reviewed some of the recent advances in recording media (e.g., oriented and antiferromagnetic coupled media) that have helped magnetic recording to maintain the areal density growth rate.
References
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Journal ArticleDOI
A Mechanism of Magnetic Hysteresis in Heterogeneous Alloys
Edmund C. Stoner,E. P. Wohlfarth +1 more
TL;DR: In this paper, the effect of shape anisotropy on magnetization curves was studied for the case of ellipsoidal spheroids of revolution (e.g., ellipses of revolution).
Journal ArticleDOI
New material for permanent magnets on a base of Nd and Fe (invited)
TL;DR: In this paper, a new compound composed of Nd, Fe, and a small quantity of B (about 1 wt. %) has been found, which has a tetragonal structure with lattice constants a=0.880 nm and c=1.221 nm.
Journal ArticleDOI
Thermal Fluctuations of a Single-Domain Particle
TL;DR: In this article, the Langevin equation of the Fokker-planck partial differential equation is replaced by a random-field term, which can be avoided by using the fluctuation-dissipation theorem.