Micromagnetic simulations using Langevin dynamics studying thermal field correlations

In micromagnetic simulations using the Langevin dynamics thermal field Hfl is usually assumed to be δ-correlated in space and time. However, non-trivial correlations of Hfl may (i) exist due to thermal bath correlations (for ultrafast processes) and (ii) arise from the discretization of the problem. We show that the unavoidable elimination of magnons with the wavelength smaller than the grid cell size leads to significant space and time correlations of Hfl. We suggest a procedure for a generation of Hfl with required correlations, thus allowing to take them into account