Swept frequency permeameters for measuring the complex, off-diagonal permeability tensor components of anisotropic, thin magnetic films

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Abstract
To better understand wave propagation through magnetic media we have measured the high-frequency off-diagonal permeability tensor components of magnetic thin films using a thin-film permeameter. Although the off-diagonal components are commonly considered to be of negligible value, for some materials they are substantial, of a magnitude comparable to that of the diagonal terms. Since the out-of-plane off-diagonal coupling terms are primarily imaginary below resonance, and real above, they may introduce unexpected phase errors into the read/write process of magnetic recording and bulk material measurements and are therefore worthy of attention. The permeameters used to measured the off-diagonal terms are based upon the design of C. A. Grimes, P. L. Trouilloid, and R. M. Walser [IEEE Trans. Magn. MAG-24, 603 (1988)], which measure diagonal terms, but with different pickup coil and sample seat geometries. For z normal to the film, and with x and y defining, respectively, the hard and easy magnetization axes of the basal plane we measure μxy and μxz. A microwave scattering parameter test set is used to measure the scattering parameters of the jig from which the complex permeability is determined. The permeameters reported on here operate over the frequency range of approximately 10–600 MHz, and have a low level permeance detection limit of about 1 μm. Measurements of cosputtered amorphous Co55Zr45 thin films show that the out-of-plane permeability coupling term μxz is a significant fraction of the basal plane hard axis permeability.