Some nontrivial aspects of the magnetic and structural characterization of hard-magnetic nanoparticles are investigated. Dilute ensembles are well-described by mean-field theory, although there is an asymmetry between exchange and magnetostatic interaction fields. Corrections to the mean-field approximation are caused by cooperative effects and have the character of Onsager reaction fields, which are much stronger in micromagnetism than in atomic-scale magnetism. The slow dynamics of zero-field-cooled (ZFC) magnetization curves is strongly affected by the particles0 magnetic anisotropy, which reduces the corresponding energy-barrier height from 25 to 19.1 kBT.
Skomski, Ralph, Balamurugan Balamurugan, Tom A. George, Mircea Chipara, Xiao-Hui Wei, Jeff E. Shield, and David J. Sellmyer. "Hysteresis and relaxation in granular permanent magnets." Journal of Applied Physics 111, no. 7 (2012). http://dx.doi.org/10.1063/1.3672845
Journal of Applied Physics