High Anisotropy CoPtCrB Magnetic Recording Media

Abstract

We describe the synthesis, magnetism and structure of CoPtCrB alloys with Pt concentrations from 10 -43 %. The Cr concentration in the alloys was 15-17 % and the B concentration was 9-11 %. The magnetic anisotropy and coercivity increase with increasing Pt up to M 30%, plateau at M 35,000 Oe and w 6000 Oe, respectively, and then decrease. Transmission electron microscopy results show the media form fine, isolated grains for all Pt concentrations. X-ray diffraction measurements show that with increasing Pt an fee Co-alloy phase is progressively formed at the expense of the hcp Co-alloy and that this fraction becomes significant for > 35% Pt. The formation of the fee phase likely causes the behavior in the anisotropy. No Pt concentration dependence is observed for the stacking fault density. The X-ray data show that with increasing Pt the CoPtCrB alloy lattice parameters exhibit two distinct regions with the slope changing at 16 % Pt. The presence of these two regions is discussed.

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“…We take parameters corresponding to a material with a relatively small saturation magnetization and high PMA such as CoPtCrB [77]. The critical current density [76] is…”

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“…An additional consequence of incrementing the atomic concentration of larger atoms into the hcp-Co unit cell is a structural transformation from hcp to fcc as reported by Toney et. al [29] for the case of Pt substitutional doping of CoCrPtB alloys. Said structural transformation is driven by strain-relaxation and was observed for a Pt content above 35%.…”