The intrinsic switching field of single domain ferromagnetic particles

The intrinsic switching field defined as the minimum field to induce spontaneous magnetic reversal is calculated at finite temperatures for a uniaxially anisotropic single domain particle using a formalism based on the generalized free energy function of the system. For a fine ferromagnetic particle coupled to a constant temperature heat bath, the switching field is smaller than the field predicted by the Stoner-Wohlfarth (SW) theory and the difference is dependent on the direction of the applied field resulting in breaking of the symmetry of the SW astroid.