Effect of C Replacement on Magnetic Properties and Nanostructure of FePt-Nitride Granular Film for HAMR Media

The effect of adding carbon (C) grain boundary material (GBM) on magnetic properties and nanostructure of FePt-nitride granular films with various nitrides is reported. The saturation magnetization of FePt-nitride-C granular films shows a similar tendency with that of FePt-nitride granular films which varies almost linearly against volume averaged melting point (
${T} _{m}^{\text {ave}}$
) of the GBM. The values of perpendicular magnetic anisotropy and degree of order of
$\text{L}1_{0}$
-FePt phase for all FePt-nitride granular films are enhanced and the amount of magnetic grains with the
${c}$
-axis parallel to the film plane is reduced when nitride is partially replaced with C. Furthermore, by replacing nitride with C, the grain-to-grain separation is promoted significantly. When the
${T} _{m}^{\text {ave}}$
of the GBM increases from around 2500 °C to 3500 °C, in general, the average cluster diameter (CD) and cluster boundary (CB) decrease from around 13 to 9 nm and from 12 to 5 nm, respectively. Considering of
${T} _{m}^{\text {ave}}$
of the GBM, these results suggest that the GBM with high
${T} _{m}^{\text {ave}}$
will solidify prior to FePt which acts as the nucleation site to reduce the CD, which is similar to CoPt-based alloy granular films.