High frequency soft magnetic performance on magnetically isotropic Co-Al-N films in external bias field

We have investigated the high frequency soft magnetic properties (μ-f properties) of magnetically isotropic Co ₇₆Al ₁₁N ₁₃ films with an external bias field (H _ex) applied in various directions. The films are prepared by rf sputtering and consist of fine Co grains 5 nm in diameter in an amorphous AlN matrix. The films have relatively large magnetic anisotropy perpendicular to the film plane and are magnetically soft. The initial magnetization curve in the film plane varies slightly with changes in the direction of the magnetizing field. A clear peak of permeability (μ″) was found at a resonance frequency (f _r) around 2.5 GHz when the film had been magnetically saturated normal to the rf-field (H _rf) in the film plane before measurement. After being magnetically saturated parallel to H _rf, the film shows a broad peak in μ″ around 9 GHz; however f _r decreases to 2.5 GHz with increasing H _ex normal to the film plane. Control of f _r between 2.5-9.65 GHz was achieved by changing the direction of H _ex, which is attributed to the direction changes in magnetic moments of a magnetically isotropic film.