Herein, we report a systematic study on the microstructure evolution of FePt-C granular films grown on MgO(0 0 1) single-crystalline substrates, especially during the initial growth stage. The number density of the grains during the nucleation stage is strongly affected by the growth temperature, reaching 40 Tgrain/in2 at <200 °C and decreasing with further increasing temperature. The addition of carbon (C) as a segregant substantially reduced the density. Despite the high number density during the nucleation stage, the density was dramatically reduced with subsequent growth of the FePt-C film. The possible reason for the reduction in the grain density is the surface diffusion of the C added to enhance grain separation. Controlling the growth conditions rather than the nucleation stage is key to increasing the areal density of FePt-C granular films to develop heat-assisted magnetic recording media.
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