High-frequency resistivity of soft magnetic granular films

Co-Zr-O granular films were prepared by reactive sputtering. The films show strong uniaxial in-plane anisotropy as well as good soft magnetic properties and high dc resistivity. In order to confirm their electrical characteristics at high frequency, the frequency and current density dependences of resistivity were investigated. Resistivity was found to be constant over the range measured (up to 18 MHz and 100 MA/m²). Furthermore, the films exhibit virtually no hysteresis along the hard-axis direction and have very little anisotropy dispersion. The frequency dependence of the initial permeability was measured and used to predict the power loss expected when granular films are used as high-frequency core materials for film inductors. The power loss is predicted to be lower than that of commercial NiZn ferrite for high-frequency applications.