Resonance features in the permeance spectra of NiFe stripes

High-frequency performance of a recording-head material can be inferred by measuring the frequency dependence of the film permeance. We employ a simple technique, using the complex impedance measurement of a sample-containing solenoid, to investigate the permeance of NiFe films patterned into stripes as a function of the frequency (up to 500 MHz), the field-excitation amplitude (up to 4 Oe) and the stripe width. Measurement of the large- and the small-signal permeances should be indicative of the material response during the writing and the reading operations. Besides the obvious interest in the frequency roll-off of the permeance, the frequency dependence of the response phase is particularly interesting because it provides insight into the power-dissipation mechanisms which degrade the flux transport capability of the material. Stripe-shaped samples facilitate the study of the magnetic film response in a simple enough geometry to permit the analysis without having to consider complications like the non-uniform demagnetizing field distribution present in a real head. At the same time, a stripe exhibits a hysteresis loop which can differ greatly from the loop of the metal film prior to patterning. This can occur because of the stress-anisotropy and the larger domain-wall density in the patterned film. Both factors are also present in heads; therefore, measurement of the frequency-dependent stripe response represents a significant step towards improving the understanding of head dynamics.