Time Dependence of Magnetic Anisotropy at Finite Temperature for Homogeneous and Composite Media

A simple torque-based method for calculating the transient behavior of temperature-dependent magnetic anisotropy is introduced. Using this method we obtain several physical quantities at finite temperature, including effective anisotropy, anisotropy field, and their fluctuations, that are crucial to heat-assisted magnetic recording (HAMR). We show that use of a composite grain that includes a high Curie temperature soft layer reduces the anisotropy fluctuations.