Search for high moment soft magnetic materials: FeZrN

Abstract

FeN materials exhibiting high moment, low coercivity and small magnetostriction have previously been reported. Zr has been known to reduce the magnetostriction in other Fe alloys. The criteria for an ideal recording head pole material as well as shields for magnetoresistive sensors include high moment, low coercivity, high permeability, and zero magnetostriction. We present here the properties of 0.3 μm thick rf sputtered FeZrN films measured as a function of the N2 partial pressure. The films were deposited at a pressure of 3 mT using a Perkin Elmer sputtering system. The target was composed of Fe with Zr chips covering approximately 2% of the surface area. The easy axis and hard axis coercivities show minima of 1.8 and 0.6 Oe, respectively, at 7–10 % N2 partial pressure with a saturation magnetization of about 18 kG. The magnetic anisotropy field is approximately 5 Oe yielding a dc permeability of approximately 4000 along the hard axis. X-ray data reveal a systematic change in the ratio of α–Fe and γ–Fe4 N; the amount of the γ–Fe4N phase increasing with increasing N2 partial pressure. The magnetostriction increases with increasing N2 content crossing zero at approximately 6%. The grain size, as probed by atomic force microscopy, is an increasing function of the N2 partial pressure; from a few nm for N2 partial pressures of 5% to being as large as 50 nm for a partial pressure of 15%. The surface roughness is about 1 nm.