Abstract
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.
