Growth Mechanism of Columnar Grains in FePt-C Granular Films for HAMR Media Processed by Compositionally Graded Sputtering

The optimization of nanogranular FePt-C films for heat-assisted magnetic recording is carried out by varying processing conditions for compositionally graded sputtering. Microstructures and magnetic properties of the films were studied for various thicknesses ranging from 2 to 12 nm to observe the growth steps of the films. An excellent in-plane nanogranular microstructure is obtained for the films of thickness ≥8 nm. Below 6 nm in thickness, the grains are random in shape and the presence of fine grains deteriorates the magnetic properties on account of poor L1₀ ordering. During the nucleation and grain growth stages, the grain size does not change too much with increasing the film thickness. But, the coarsening of FePt grains occurs and the aspect ratio of the FePt grain changes in the films of thickness ≥8 nm. We achieve a minimum grain size of 6.2 nm having an aspect ratio of 1.9 with a large perpendicular coercivity of 3.9 T for ∼ 12 nm thick FePt-C films.