Grain density control in FePt granular films for heat-assisted magnetic recording media

Abstract

To realize high areal density hard disk drives (HDDs) larger than 4 Tbit/in2, ultrafine FePt grains of less than 5 nm and grain density larger than 24 T/in2 are required. Although there have been many investigations to reduce the grain size of FePt, there are few reports on the control of grain density. To increase the grain density, we focused on three aspects of the surface morphology and grain density: nucleation sites on the substrate surface, surface free energy, and lattice mismatch. We achieved 14 T/in2 by maximizing the number of nucleation sites in the FePt-C granular film and found that the surface free energy and lattice mismatch are crucial parameters for controlling the grain density.