| The magnetic layers in the current high density magnetic thin film recording media are based on Co-Cr based alloys with ternary and quaternary additions of Pt, Ta, and/or B. Enhancing storage densities requires a better understanding of the roles of these additions. The structure and magnetic properties of bulk (i) CoCr binary alloy, (ii) CoCrB ternary alloys, and (iii) CoCrBPd, CoCrBTa, and CoCrBPt quaternary alloys were examined here to understand (i) the role of boron in CoCrB ternary system, and (ii) the role of palladium, tantalum, platinum, and boron in CoCrBPd, CoCrBTa, and CoCrBPt quaternary alloy systems.; Thirty-three bulk alloys were systematically designed, prepared and examined. In these alloys, Pd and Ta contents were between 0 and 9 at. % and B and Pt contents varied from 0 to 6 at. %. Optical microscopy was performed to evaluate the grain size in these alloys. X-ray diffraction work was performed to determine (i) the variations in lattice parameters of the hcp phase with alloy additions, and (ii) the solubility limits and the formation of second phases. A vibrating sample magnetometer was used to measure the changes in the saturation magnetization.; B had negligible solubility in the hcp phase of these cobalt alloys and is mainly present in the elemental form in the grain boundary region, and as a nonmagnetic second phase. B is a very effective grain refiner at concentrations of <0.5 at %. Significant variation of lattice parameters of the hcp phase with Pd, Ta, and Pt addition shows that they will influence magnetocrystalline anisotropy. Pd and Pt were soluble in the hcp phase at concentration levels investigated, while solubility limit of Ta was <3 at. % indicating greater grain boundary segregation of Ta compared to Pd and Pt. Ta like B was more effective than Pd and Pt in refining the grains. Ta should be controlled to <3 at. % to minimize the reduction in saturation magnetization and to minimize the formation of a second phase. From a grain refinement point of view, Pd should be controlled to 6 at. %, and no specific limit on Pt is suggested. |
