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Investigation of magnetic properties and nanostructure of FePt-B2O3 granular film with carbon buffer layer (BL) of various thicknesses is reported. When the thickness of carbon BL is varied from 0 to 0.6 nm, saturation magnetization (Msfilm) is almost constant at around 750 emu/cm3 and perpendicular magnetic anisotropy (Ku⊥film) changes from around 1.0×107 to 2.0×107 erg/cm3. For the granular film with the carbon BL thicker than 0.6 nm, both Msfilm and Ku⊥film decrease. The reduction of Msfilm for the granular film by adding a carbon BL may be due to the alloying of carbon into the FePt magnetic grains. The enhancement of Ku⊥film for the film with a 0.6 nm carbon BL is considered due to the reduction of the in-plane texture component which is supported by the in-plane XRD. The reduction of Ku⊥film for the film with a carbon BL thicker than 0.6 nm is considered due to random growth of magnetic grains on a continuous carbon BL which is supported by the TEM cross-section images. According to these results, the employment of an un-continuous thin carbon BL is a promising method to enhance c-axis texture orientation of the FePt-oxide granular films.

A systematic investigation of the magnetic properties and nanostructure of FePt-nitride granular films with nitride of various melting points (Tm) is reported. When Tm of nitride grain boundary materials (GBMs) is varied from 1650 to 3305 °C, the saturation magnetization (Msfilm) changes from 710 to 570 emu/cm3. The Msfilm of FePt-nitride is similar to that of FePt-oxide granular films, almost varies linearly against Tm. At almost the same Tm, FePt-nitride shows a higher Msfilm of around 70 emu/cm3 compared to that of FePt-oxide granular films. According to the torque measurement result of the saturated torque coefficient with fourfold components (L4θsat), FePt-nitride shows a smaller L4θsat than that of FePt-oxide granular films, which suggests that FePt-nitride has a smaller content of the in-plane component than that of FePt-oxide granular films. This is supported by the in-plane x-ray diffraction profile measurement, where FePt-nitride has a smaller integral intensity of (001) diffraction of the L10-FePt phase than FePt-oxide granular films. With further promotion of grain separation, nitrides are more promising GBMs than oxides due to their high Msfilm and smaller content of the in-plane component.