2013/12/31 by S. Bance, Simon Bance, Johann Fischbacher +6 · 1 citation
Materials Science · Physics and Astronomy · #Anisotropy #Aspect ratio (aeronautics) #Coercivity #Composite material #Condensed matter physics #Ferromagnetism #Field (mathematics) #Magnet #Magnetic Properties of Alloys #Magnetic and transport properties of perovskites and related materials #Magnetic anisotropy #Magnetic field #Magnetic properties of thin films #Magnetization #Magnetocrystalline anisotropy #Materials science #Micromagnetics #Optics #Physics #RADIUS #Single domain #cond-mat.mtrl-sci
paper · pdf · doi:10.1016/j.jmmm.2014.03.070
published as Journal of Magnetism and Magnetic Materials Volume 363, August 2014, Pages 121-124 · 3 pages, 4 figures
arxiv created 2014/03/26 · openalex publication_date 2014/04/03 · arxiv updated 2016/03/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
In the search for rare-earth free permanent magnets, various ideas related to shape anisotropy are being pursued. In this work we assess the limits of shape contributions to the reversal stability using micromagnetic simulations. In a first series of tests we altered the aspect ratio of single phase prolate spheroids from 1 to 16. Starting with a sphere of radius 4.3 times the exchange length Lex we kept the total magnetic volume constant as the aspect ratio was modified. For a ferromagnet with zero magnetocrystalline anisotropy the maximum coercive field reached up to 0.5 times the magnetization Ms. Therefore, in materials with moderate uniaxial magnetocrystalline anisotropy, the addition of shape anisotropy could even double the coercive field. Interestingly due to non-uniform magnetization reversal there is no significant increase of the coercive field for an aspect ratio greater than 5. A similar limit of the maximum aspect ratio was observed in cylinders. The coercive field depends on the wire diameter. By decreasing the wire diameter from 8.7 Lex to 2.2 Lex the coercive field increased by 40%. In the cylinders nucleation of a reversed domain starts at the corners at the end. Smoothing the edges can improve the coercive field by about 10%. In further simulations we compacted soft magnetic cylinders into a bulk-like arrangement. Misalignment and magnetostatic interactions cause a spread of 0.1 Ms in the switching fields of the rods. Comparing the volume averaged hysteresis loops computed for isolated rods and the hysteresis loop computed for interacting rods, we conclude that magnetostatic interactions reduce the coercive field by up to 20%.