Recording process in high frequency field

We study the dynamic recording process due to the write head driven by high frequency signal currents. The magnetizations of a medium recorded with fields at several frequencies from 100 MHz to 500 MHz are calculated by using the Landau-Lifshitz-Gilbert equation. As the frequency increases, the normalized rise time of the head field increases proportionally. The bit shift becomes large at high frequencies due to the delay. The peak value of the head field decreases with the delay, so that the magnetization reversal cannot occur at high frequencies. The saturation magnetic flux density of the head tip is almost independent on the rise time. So, the peak value of the head field does not increase at frequencies of more than 400 MHz as the saturation flux density increases.