Integral relaxation time of single-domain ferromagnetic particles

The integral relaxation time τᵢₙₜ 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 τᵢₙₜ^-1 from the lowest eigenvalue of the Fokker-Planck equation Λ₁ 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. {} 1996 The American Physical Society.