Thermal reversal of magnetic nanoparticles with the quartic anisotropy

The effect of the quartic anisotropy on energy barriers and thermal reversal modes is studied in a system of two interacting single-domain particles. It is assumed that the two particles possess identical volumes and uniaxial anisotropies. The lowest energy barriers to be overcome for magnetization reversal are determined by saddle points of the energy surface. The presence of the quartic anisotropy results in a change in the locations of the saddle points, and then the reversal modes under thermal excitation, which is illustrated by the energy surface and corresponding contour plots of the two single-domain particles. In the presence of the quartic anisotropy, the energy barriers are calculated analytically for the coherent rotation and the symmetric fanning rotation modes.