Superparamagnetic relaxation times for mixed anisotropy and high energy barriers with intermediate to high damping: 2. Uniaxial axis in a 〈111〉 direction

Superparamagnetic relaxation rates are calculated for ferromagnetic particles with mixed cubic and uniaxial anisotropy. In part 1 the uniaxial axis is in a 〈001〉 crystallographic direction, while in this article it is in a 〈111〉 crystallographic direction. When K u = 0, there are six remanent states but only one relaxation rate. As K u increases, the remanent states converge on the uniaxial axis, merging with it at K u = 0.76 K ′ 1 for K ′ 1 > 0 and at K u = 0.22 ∣ K ′ 1 ∣ for K ′ 1 < 0. In between the components parallel and perpendicular to the uniaxial axis relax at different rates. The rate for the perpendicular component increases with K u . If all the remanent states have the same energy, there is a single, decreasing rate for the parallel component. However, for some values of K u and K ′ 1 there are two states with two different energies. There are then two rates, one decreasing and one increasing. For large K u the remanence is uniaxial. In this article and part 1 the relaxation rates have an exponential and a prefactor. The prefactors are calculated in the high energy barrier, intermediate‐ to high‐damping approximation. For elongated particles the prefactor is smaller than predicted by the Néel‐Brown theory for uniaxial particles. The predicted relaxation rates are the same order of magnitude as experimental estimates for maghemite and magnetite. Better agreement cannot be expected because order‐of‐magnitude uncertainties still exist in both the experimental and theoretical estimates.