Trial Production of the High Frequency Permeance meter

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The magnetic recording technology trend is towards increasingly higher recording density and higher data rates. Then magnetic thin films for read-write heads are required to exhibit a high permeability in still higher frequency region. In this project, the measurement of the high frequency permeability of soft magnetic thin film was investigated in ultra high frequency range up to 1GHz.The effective permeability of magnetic films were estimated from the change of impedance before and after inserting the film into a coil or strip line using a rf impedance meter (YHP419A). Considering the resonance frequency of the measurement circuit as well as the sensitivity of the impedance meter, among various coils and strip lines with different reactance, suitable ones were chosen depending on the frequency of the measurement. The real and imaginary parts of permeability were determined using the equivalent circuit. By using a short strip line, it became easy to measure the permeability up to 1GHz. As a result, it was found that the frequency response was improved in CoZr/SiO_2 multilayr and loss part at low frequency was much deduced in the multilayr. In the very thin film, the frequency response was further found to become much better than thicker and multilayr films. The real and imaginary parts cross with each other at about the resonance frequency calculated from Kittel's equation.