Thermal and magnetic properties of Hf-containing HITPERM alloys

It is known that Hf addition reduces the coercivity of nanocrystalline soft magnetic alloys more effectively than Zr and Nb as the inhibitor of grains growth. In this paper, the differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM) were used to evaluate the influence of Co content on the crystallization process, soft magnetic properties and structure of (Fe1−xCox)86Hf7B6Cu1 (x=0–1) alloys. The coercivity was determined from the quasi-static hysteresis loop measured at room temperature and high temperatures. The Fe-containing alloys studied exhibit typical two-phase structure of nanocrystals embedded in an amorphous matrix with high crystalline volume fraction after the primary crystallization. The moderate Co addition enhances the saturation magnetization, but the coercivity also increases with Co addition. Among the alloys studied, the x=0.4 and 0.5 alloys exhibit both the low coercivity with good thermal stability and large saturation magnetization at high temperatures, which are excellent candidates for the high temperature applications in temperature range from 500 to 550 °C.