Microstructural and magnetic characterization of rapidly solidified and annealed Pt–Co–B alloys

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Abstract
Significant increases in intrinsic coercivity (H ic) of Pt–Co alloys have been obtained by the addition of boron and the application of rapid solidification processing. After rapid solidification by double anvil splat quenching with subsequent annealing at 650 °C for 30 min, an alloy of Pt42Co45B13 (at. %) exhibits an H ic as high as 14 kOe. Transmission electron microscopy and Lorentz microscopy were used to interpret the magnetic data. Annealing of the Pt–Co–B influences the L10 superlattice structure and grain size of the matrix, the crystal structure and size of Co‐boride precipitate, and the distribution of magnetic domain walls. A microstructural analysis shows that the maximum H ic occurs when Co borides, having the Co3B structure, are within the single magnetic domain size. The magnetic hardening mechanism in Pt–Co–B is believed to be a combination of inhibited magnetic domain nucleation and difficult reverse magnetic domain growth caused by the interaction of the magnetically anisotropic Co borides with the L10 Pt–Co matrix.