Enhancement of the Curie temperature of the amorphous intergranular phase inSm–Fe–Ga–C nanocomposite permanent magnetic materials

Abstract

The magnetic properties of the nanocomposite permanent magneticmaterials Sm–Fe–Ga–C have been investigated. As-quenchedSm2Fe18Ga2C2.2 samples prepared with a substrate velocityvs = 18.5and 19.5 m s−1 contain some amorphous intergranular phase, togetherwith Sm2Fe15Ga2C2.2 (Th2Zn17-type structure) and α-Fe. On the basisof the compositional dependence of the Curie temperature in Sm2 Fe15+x Ga2C2.2amorphous ribbons, an enhancement of the Curie temperature of the amorphousintergranular phase (aip) was found in nanocomposite alloys with respect toamorphous ribbons of the same composition.57Fe magnetic hyperfine fielddistributions for the amorphous intergranular amorphous phase are narrower thanthose for the amorphous ribbon. No difference was found in average hyperfinefield, and hence in Fe magnetic moment, within the experimental error. We alsoexcluded the effect of compositional difference on Curie temperature. Theenhancement of the Curie temperature is thus concluded to originate from thepenetration of the molecular field of crystallized magnetic phases into theamorphous intergranular region. Finally, a theoretical model was proposed toexplain the mechanism of ‘extra’ enhancement of the Curie temperature.