Dependence of switching coefficient on damping constant of thin-film magnetic recording media

Abstract

We have investigated the relationship between the switching time of thin film media and the Gilbert damping constant α through numerical calculations. The switching coefficient, Sw (the required energy for switching) of thin-film media was estimated from the time integration of the external field over switching field, Hcro(∫[H(t)−Hcro]dt). With decreasing α, Sw of a two-dimensional random thin-film medium with an uniaxial anisotropy field Hk of 6.5 kOe, reached a minimum (fastest) value of 50 ns Oe at α of about 0.1 and then increases slightly to 88 ns Oe at α=0.03. This value was nearly equal to the Sw value of 101 ns Oe at α=1.0. The value of α (about 0.1) that gave a minimum Sw did not change significantly with Hk or saturation flux density Bs. We showed analytically that the value of α for the fastest switching was less than 1.0, when an effective field was applied in a direction different from the easy axis of a magnetic grain. The switching time was in proportion to the rate of Sw/Hk of a thin-film media. These results show that high-speed recording at frequencies of up to 1 GHz can be achieved at α=0.03 in terms of the switching time of longitudinal thin-film media.