Intergrain magnetic coupling and microstructure in CoPtCr, CoPtCrTa, and CoPtCrB alloys

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Abstract
We have investigated intergrain magnetic interactions in three types of Co-based alloys of interest for longitudinal magnetic recording: CoPtCr, CoPtCrTa, and CoPtCrB. The goal is to quantify how intergranular exchange interactions in CoPtCr alloys are modified by doping said alloys with additives such as Ta and B. These 20-nm-thick alloys were grown under identical deposition conditions on AlMg/NiP substrates and a comprehensive study of their microstructural and magnetic properties was conducted to evaluate the degree of intergranular exchange coupling and the manner how the coupling depends on the corresponding microstructural properties. We find that the ternary alloy exhibits the strongest intergrain coupling. In the case of the quaternary alloys, the degree of exchange interactions is virtually the same. Consequently, any significant difference pertaining recording performance in these quaternary alloys must be dominated by the inherent differences in grain microstructure and the spatial distribution of the alloy constituent elements.