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 Co76Al11N13 films with an external bias field (Hex) 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 (fr) around 2.5 GHz when the film had been magnetically saturated normal to the rf-field (Hrf) in the film plane before measurement. After being magnetically saturated parallel to Hrf, the film shows a broad peak in μ'' around 9 GHz; however fr decreases to 2.5 GHz with increasing Hex normal to the film plane. Control of fr between 2.5-9.65 GHz was achieved by changing the direction of Hex, which is attributed to the direction changes in magnetic moments of a magnetically isotropic film.