Effects of surface anisotropy on hysteresis in fine magnetic particles

We solve numerically the dissipative Landau-Lifshitz-Gilbert equations to consider hysteresis in fine magnetic particles. Finite-size effects are studied for two models with uniaxial anisotropy—bulk random axis and surface anisotropy only. It is demonstrated that the latter model introduces considerable effects for small enough particles when the coupling to the anisotropy is equal or greater than the coupling to the isotropic Heisenberg exchange. We show that some features of magnetization reversal are associated with spins at the surface of fine particles.