The effect of uniaxial quartic anisotropy on thermal stability of magnetic nanograins

The effect of quartic anisotropy (K-2) for nanograins with hexagonal crystalline structure on thermal stability has been studied. For reversal field parallel to the anisotropy axis, the presence of K-2 increases the energy barrier in small fields but does not change the nucleation field. The mean first passage time was calculated from the stochastic differential equation. Reversal field at a finite temperature versus field pulse time showed very little effect at short times but thermal stability at long times was significantly extended. This effect was shown to be appreciable only for fields oriented within about 15 degrees to the anisotropy axis. (C) 2001 American Institute of Physics.