Brownian and Néel relaxation times in magnetic particle dynamics

Abstract

The equations for the well-known Brownian and Néel relaxation times T_B and T_N (given in the Introduction) are not sufficient to determine whether or not the Néel relaxation mechanism may be neglected. In fact, for a sufficiently large magnetic field strength, the Néel relaxation time can change by many orders of magnitude, whereas the Brownian relaxation time is comparatively insensitive to the magnetic field strength. Therefore, even if τ_N >> τ_B, the Néel relaxation mechanism can still be important and even dominate.