Thermal relaxation of clusters of interacting Stoner-Wohlfarth particles

The relaxation of the total magnetization of a cluster of identical Stoner-Wohlfarth particles on a cubic lattice is studied by solving the Langevin Landau-Lifshitz equation which incorporates thermal fluctuations into the full dynamics of the magnetization. The resultant ordinary differential equations are numerically integrated with the stochastic Euler method. In the computation, the particles are located at nodal points of a 12x12x12 lattice (total 1728 nodes). All particles have uniaxial anisotropy and the easy axes are aligned in the same direction. The interaction between particles is dipolar. The relaxation of the magnetization is calculated. Initially, the magnetization in all particles is aligned in the up direction. Due to thermal fluctuations, the average magnetization decays. Simulations show that the speed of decay is faster when the interaction between particles is stronger. Furthermore, the magnetization decays exponentially without interaction. As the interaction between particles increases, the decay is no longer exponential and apparently there are two or more relaxation time scales present. (C) 2000 American Institute of Physics. [S0021-8979(00)78208-9].