Eddy currents and displacement currents in multi-layer soft magnetic films for recording heads

An explanation of the magnetic properties of multilayered soft magnetic films is given from the viewpoint of mutual inductance, eddy current loss, and magnetic domain structure variation. The frequency response of the permeability was measured in several multilayered films. In order to clarify the variation of properties from sample to sample, 3-D-FEM (finite-element method) calculations including a time-dependent term were carried out. The permeability is found to decrease with decrease of insulator thickness because of the increase of the mutual inductance. One of the most important factors in decreasing the permeability is the phase difference between the surface and the inside of magnetic layer. If the metal film overlaps the insulator edges, the permeability is found to decrease due to an increase in eddy currents. Magnetic domain shape is shown to be correlated with the strip width and the insulator thickness