Thermodynamic behavior of nanomagnets with a vortex configuration

The thermodynamic behavior of flat circular nanomagnets with a vortex domain configuration is studied using Langevin dynamics simulations for the dynamical behavior as well as local mean-field calculations for equilibrium properties. Our studies show that the vortex core becomes thermally unstable with increasing temperature, acting like a superparamagnetic system. On time scales where the vortex core remains within one of the metastable states it still has a stronger temperature dependence than the magnetization far away in the bulk of a domain.

Figure 1

(Color online) Superparamagnetic behavior of the vortex core: Magnetization of the vortex core vs time for different temperatures. The system diameter is 35 spins, $\omega ∕J=0.2$.

Figure 2

(Color online) First switching time vs inverse temperature for different values of $\omega ∕J$. The system diameter is 35 spins.

Figure 3

(Color online) Temperature dependence of different magnetization components inside and outside the vortex core for the case of a system diameter of (a) 35 spins and (b) 32 spins. $\omega ∕J=0.2$.

Figure 4

Breakdown of the core magnetization: out-of-plane magnetization in the central part of the disk for different temperatures corresponding to Fig. 3a.