MAGNETIC VISCOSITY IN HIGH-DENSITY RECORDING

For future ultrahigh-density magnetic recording, the magnetic viscosit y in thin-film media will become an issue due to the drastic reduction in grain size. An algorithm combining a Monte Carlo method and molecu lar dynamics was employed to study the thermal effects in thin-film me dia. 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 ra te and the elapsed time. Hysteresis loops for various K(u)V/kT ratios and sweep times are simulated. Isolated and di-bit transitions are wri tten, taking into account thermally assisted switching. After the head field is, turned off, the subsequent thermal decay is computed for ti me spans as long as 6 months. Significant aftereffect is found for gra in volumes about twice that for ordinary superparamagnetism.