Magnetometry-based order parameter to probe the A1 to L10 transformation in FeCuPt for heat-assisted magnetic recording media

High magnetic anisotropy materials such as L1₀ FePt alloys are particularly sought after for the emerging heat-assisted magnetic recording (HAMR) media. A critical challenge has been the elevated annealing temperature (typically above 6000C) necessary to transform the as-deposited cubic A1 phase into the ordered L1₀ phase, which is often incompatible with the rest of the manufacturing processes. Another key issue is the stringent requirement on switching field distribution for ultrahigh density HAMR media, where residual A1 phase could be detrimental. Therefore, a complete understanding of the low anisotropy A1 to high anisotropy L1₀ phase transformation is critical. In prior studies, an order parameter S is often used to characterize the degree of the L1₀ ordering, using properly corrected, integrated intensities of the x-ray diffraction (XRD) peaks, since differences in lattice occupation are manifested in the structure factor. This is an elaborate, time consuming process, yet its applicability still has significant limitations, e.g., for textured samples or materials with poor crystallinity, and for samples with tiny amount of minority phases.