High anisotropy CoPtCrB magnetic recording media

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 ≈30%, plateau at ≈35 000 Oe and ≈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 a face-centered-cubic (fcc) Co-alloy phase is progressively formed at the expense of the hexagonal-close-packed Co-alloy and that this fraction becomes significant for >35% Pt. The formation of the fcc 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.