The effect of melting point (Tm) of various grain boundary materials (GBMs) on the magnetic properties and nanostructure of FePt granular films was investigated. According to the analysis for the granular films with a constant GBM volume of 30 vol% deposited at a high substrate temperature, the saturation magnetization, Ms, had a strong correlation with Tm. We newly proposed a degree of order evaluation from in-plane X-ray diffraction from the L10 FePt (110) and (220) planes. As the results, neither the degree of order nor the grain diameter had any significant correlation with the Tm of GBM. Based on these analyzes, it was found that an increase of the grain diameter increases the degree of order, which results in enhancement of the coercivity of the FePt granular films. And it was clarified that Ms strongly depends on the degree of phase separation related to the melting point of GBM.
The magnetic properties and structures of Co80Pt20–30 vol % oxide (ZrO2, Cr2O3, Y2O3, Al2O3, MnO, TiO2, WO2, SiO2, Mn3O4, WO3, Co3O4, MoO3, and B2O3) granular media deposited at room temperature were investigated. As a result, the following were found. 1) By employing oxides with low melting point temperatures as the granular media, magnetic grains with high saturation magnetization (
) and perpendicular magnetic anisotropy (
) are obtained; the increases in
and
are due to the promotion of the columnar growth of magnetic grains and phase separation or two-phase precipitation between magnetic grains and oxides. 2) The increase in the
of the granular media followed by the decrease in the melting point of oxides is due to the reduction in the amount of stacking faults. 3) Among these granular media, the CoPt–B2O3 granular medium has the highest coercivity (H
c) and ratio of H
c to the magnetic anisotropy field (
) of 8.0 kOe and 0.4, with
and
of 1115 emu/cm3 and 1.1 × 107 erg/cm3, respectively. 4) The CoPt–B2O3 granular medium has well-isolated and columnar growth magnetic grains with an average grain size of 6.5 nm.
Investigation of magnetic properties and microstructure of granular media with various double oxides including B2O3 as the grain boundary material is reported. By adding a high Tm second oxide together with B2O3 for the grain boundary material, comparable magnetic properties with that of the single oxide granular media and smaller crystallite size evaluated by X-ray diffraction (GDinplane) than that of the single oxide granular media can be obtained. Among the evaluated media, the granular medium with B2O3− TiO2 is promising for the grain boundary material, showing comparable average Ms and Ku of 806 emu/cm3 and 7.7×106 erg/cm3 with that of the single B2O3 and smaller GDinplane of 4.8 nm than that of the single B2O3 of 5.4 nm. In the TEM image, thin grain boundaries inside the grains can be observed which indicates that small grains with one-on-one grains growth is expected when an underlayer with smaller grain size is utilized.
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