Proposed solutions to a standard problem in micromagnetics that were collected anonymously from a number of researchers using a variety of computational techniques are presented. This is the first time that a problem in micromagnetics has been attempted by a group. The sample problem is a 1 m x2 m rectangular element of Permalloy film, 20 nm thick. The material properties are specified by an exchange stiffness constant, A=1.3X10-11 J/m, a magnetization, M=8.0X105 A/m, and a uniaxial ansotropy constant, K=5.0X102 J/m3 with the easy axis directed parallel to the long edge of the sample. The requested calculations are hysteresis loops for fields directed one degree away from the long and short axes and magnetization configuration data for the remanent states. The results collected show a surprising lack of agreement. For fields applied nearly parallel to the long axis of the sample problem, calculated coercivities range from 2.4 to 33 mT, squareness values range from 0.23 to 1.00, and there is a variety of hysteresis loop shapes and magnetization patterns. Similar differences exist in the results for fields applied nearly parallel to the short axis of the sample. Differences in computational methods that give rise to the disparity in the results, e.g., grid geometry and size and magnetostatic field calculation methods, are highlighted.
Citation: Journal of Applied Physics
Issue: No. 8
Pub Type: Journals