Perpendicular Magnetic Anisotropy Analysis for L1₀-Typed FePt Granular Media with Various Grain Boundary Materials by 90 kOe Torquemetry

Perpendicular 90 kOe torquemetry analysis of magnetic anisotropy (K-{mathrm {ubot }}{mathrm {exp}} ) for L10-typed FePt granular media with various grain boundary materials (GBMs) was conducted. According to the analysis for granular films with a constant GBM volume of 30 vol% deposited at a high substrate temperature, K-{mathrm {ubot }}{mathrm {exp}} was not dependent on the saturated torque coefficient of fourfold components (L-{4theta }{mathrm {sat}} ) but was dependent on that of twofold components (L-{2theta }{mathrm {sat}} ) originating from magnetic grains with c -axes normal to the film plane. Furthermore, L-{4theta }{mathrm {sat}} mainly originated from FePt grains with c -axes parallel to the film plane. K-{mathrm {ubot }}{mathrm {exp}} also had a strong correlation with grain diameter (GD ) and degree of order (S-{mathrm {in}} ). On the other hand, K-{mathrm {ubot }}{mathrm {exp}} had no significant correlation with the melting point (T-{m} ) of the GBM, which indicates that the dominant factor affecting K-{mathrm {ubot }}{mathrm {exp}} was not phase separation. Based on these evaluations, an increase of GD caused an increase of S-{mathrm {in}} , regardless of the GBMs, which resulted in enhancement of K-{mathrm {ubot }}{mathrm {exp}} for the FePt granular films.