Bias and frequency response of the permeability of CoZrNb/SiO2 multilayers

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Abstract
Compared to single‐layer films, CoZrNb/SiO2 multilayers with amorphous, soft magnetic films exhibit increased high‐frequency response (to about 100 MHz) that is not understood. We studied single and multilayer films in this system and observed three distinct types of magnetic bias and frequency responses (phases I–III). The high‐frequency responses of phase II and III films were reduced from that of phase I. Phase changes were produced in the single‐layer amorphous CoZrNb films by varying the film thickness, and in double‐layer (N=2) and multilayer (N>2) films by varying the magnetic layer thickness. The phase boundaries in the former were shifted by magnetostatic coupling of the perpendicular component of M. These studies indicated that phase I films had uniform planar magnetizations, while phase II and III films had perpendicular components. The results are summarized in the form of a phase diagram (film thickness versus inverse film separation), which suggests that the frequency response of multilayer thin films is enhanced when the individual magnetic layers are sufficiently thin to insure a planar magnetization (phase I).