Abstract
The increasing information density in magnetic recording, theminiaturization in magnetic sensor technology, the trend towardsnanocrystalline magnetic materials and the improved availability oflarge-scale computer power are the main reasons why micromagnetic modellinghas been developing extremely rapidly. Computational micromagnetism leads to adeeper understanding of hysteresis effects by visualization of themagnetization reversal process. Recent advances in numerical simulationtechniques are reviewed. Higher order finite elements and adaptive meshinghave been introduced, in order to reduce the discretization error. The use ofa hybrid boundary/finite element method enables accurate stray fieldcomputation for arbitrary shaped particles and takes into account the granularmicrostructure of the material. A dynamic micromagnetic code based on theGilbert equation of motion to study the time evolution of the magnetizationhas been developed. Finite element models for different materials and magnetshapes are obtained from a Voronoi construction and subsequent meshing of thepolyhedral regions. Adaptive refinement and coarsening of the finite elementmesh guarantees accurate solutions near magnetic inhomogeneities or domainwalls, while keeping the number of elements small. The polycrystallinemicrostructure and assumed random magnetocrystalline anisotropy of elongatedCo elements decreases the coercive field and the switching time compared tozero anisotropy elements, in which vortices form and move only after a certainwaiting time after the application of a reversed field close to the coercivefield. NiFe elements with flat, rounded and slanted ends show differenthysteresis properties and switching dynamics. Micromagnetic simulations showthat the magnetic properties of intergranular regions in nucleation-controlledNd-Fe-B hard magnetic materials control the coercive field. Exchangeinteractions between neighbouring soft and hard grains lead to remanenceenhancement of isotropically oriented grains in nanocrystalline compositemagnets. Upper limits of the coercive field of pinning-controlled Sm-Comagnets for high-temperature applications are predicted from the micromagneticcalculations. Incorporating thermally activated magnetization reversal andmicromagnetics we found complex magnetization reversal mechanisms for smallspherical magnetic particles. The magnetocrystalline anisotropy and theexternal field strength determine the switching mechanism. Three differentregimes have been identified. For fields, which are smaller than theanisotropy field, magnetization by coherent switching has been observed.Single droplet nucleation occurs, if the external field is comparable to theanisotropy field, and multi-droplet nucleation is the driving reversal processfor higher fields.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
