Integral relaxation time of single-domain ferromagnetic particles

The integral relaxation time tau(int) of thermoactivating noninteracting single-domain ferromagnetic particles is calculated analytically in the geometry with a magnetic field H applied parallel to the easy axis. It is shown that the drastic deviation of tau(int)(-1) from the lowest eigenvalue of the Fokker-Planck equation Lambda(1) at low temperatures, starting from some critical value of H, is the consequence of the depletion of the upper potential well. In these conditions the integral relaxation time consists of two competing contributions corresponding to the overbarrier and intrawell relaxation processes.