The effect of melting point (T m) 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, M s, had a strong correlation with T m. 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 T m 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 M s strongly depends on the degree of phase separation related to the melting point of GBM.
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