Louise Desplat
The rate of thermally activated transitions can generally be described by the Arrhenius law, as k = f0 exp(-ΔE/kT) , in which ΔE is the energy barrier, and f0 is a prefactor. Within the magnetic community, it is common practice to assume a constant value of f0 as a characteristic frequency of the dynamics – typically a few GHz, and focus on the barrier to assess thermal stability of magnetic textures. In this work, we show how the activation entropy contained in the prefactor can play a crucial role in thermally activated magnetic transitions. By means of atomistic simulations, we demonstrate entropic narrowing for skyrmions, whereby the activation entropy tends to stabilize an isolated skyrmion against the collinear ground state. For the free layer of a magnetic tunnel junction, we shed light onto the Meyer-Neldel compensation phenomenon, in which fluctuations favour the domain wall configuration at the saddle point over the stable collinear state, thereby drastically reducing information retention times in memory applications.