Magnetic viscosity in high-density recording

For future ultrahigh-density magnetic recording, the magnetic viscosity in thin-film media will become an issue due to the drastic reduction in grain size. An algorithm combining a Monte Carlo method and molecular dynamics was employed to study the thermal effects in thin-film media. The component of the field perpendicular to the plane defined by the axes of shape anisotropy and uniaxial crystalline anisotropy makes it necessary to use the three-dimensional energy surface to find the minimum energy barrier. This barrier is used to sample the reversal rate and the elapsed time. Hysteresis loops for various KuV/kT ratios and sweep times are simulated. Isolated and di-bit transitions are written, taking into account thermally assisted switching. After the head field is turned off, the subsequent thermal decay is computed for time spans as long as 6 months. Significant aftereffect is found for grain volumes about twice that for ordinary superparamagnetism.