TEMPERATURE-DEPENDENCE OF MAGNETIC-PROPERTIES IN CO-PT, FE-PT AND CR-PT PERMANENT-MAGNET ALLOYS

The thermal magnetic analysis and the temperature dependence of the permanent magnet properties of CoPT, Fe-39Pt and Cr-59.2Pt alloys were investigated by using a VSM and a recording fluxmeter. The results of the thermal magnetic analysis showed that the magnetization of these alloys have the maxima at 720 K (Co-Pt), 650 K (Fe-Pt) and 1085 K (Cr-Pt). It is considered that the maximum appears to be due to the Hopkinson effect by the rapid decrease of the magnetic anisotropy near Curie temperature. The coercivities are 820 kA/m for the CoPt, 520 kA/m for Fe-39Pt and 700 kA/m for Cr-59.2Pt alloys at 4.2 K, and decreased gradually with increasing temperature. The temperature coefficients of residual flux density are -0.04%/deg for CoPt and -0.06%/deg for Fe-39Pt alloys. The Cr-Pt magnet alloys, which show a high coercivity in a narrow composition range from 58 to 60 at%Pt, exhibit a low magnetization, but a high magnetic transition temperature. It is presumed that the mechanism of the coercivity is closely related with the enhanced magnetization, because the coercivity increase with increasing magnetization.