Thermal and magnetic field effect on macroscopic quantum tunneling of a ferromagnetic particle

At finite temperature we study the quantum tunneling of a ferromagnetic particle placed in a magnetic field at an arbitrary angle. Considering the magnetocrystalline anisotropy with the biaxial symmetry, in the small epsilon(= 1- H/H-c) limit we obtain the approximate form of the WKB exponent about the crossover temperature T-c from thermal to quantum regime for the magnetic field opposite to the initial easy axis and for the field in the intermediate range of angle. Moreover, the numerical WKB exponent in the full range of temperature is presented.