‘‘Dynamic-thermal’’ reversal in a fine micromagnetic grain: Time dependence of coercivity

An analytic model for reversal field versus pulse time in a fine magnetic grain has been developed for the case when the external magnetic field H0 is parallel to the axis of uniaxial anisotropy. The expressions include both thermal fluctuations and magnetization dynamics. Therefore application is for fields both less than and greater than the intrinsic uniaxial anisotropy field HK . For the case of 2H0 /HK.1 the mean first passage time from the initial saturated state to the thermodynamically equilibrium reversed state is calculated. For the case of 2H0 /HK,1 we calculate the mean first passage time from the thermodynamically equilibrium state of the metastable well to the thermodynamically equilibrium stable reversed state. It is shown that simple Néel–Arrhenius analysis is applicable for times greater than at least 100/agHK . © 2000 American Institute of Physics. @S0021-8979~00!83508-2#