Phase lag in the high-frequency response of thin-film recording heads

The phase lag introduced by a head in the writing process was measured with a scanning Kerr effect microscope. The phase lag of thin-film heads increases rapidly with frequency even below 30 MHz. A 20° phase lag at about 20 MHz was observed on both an IBM 3380 eight-turn and a 3390 31-turn head. By studying the phase lag caused by different damping mechanisms in the magnetization processes, it was concluded that the rapid increase in phase lag below 20 MHz is primarily caused by the damping of domain wall motion in the sloped region. Different designs of the sloped region of the heads were shown to cause large differences on the phase lag. The effect of drive current amplitude on the phase lag was studied both experimentally and theoretically. The results indicate that, when eddy current damping dominates and the surface of a magnetic film is driven to saturation, a larger phase lag occurs when larger drive field is applied