Phase stability, crystal structure, and magnetic properties of NdCo7-xHfx compounds

The phase stability, crystal structure, and magnetic properties of NdCo7-xHfx (x=0.1, 0.2, 0.3) compounds were studied by means of X-ray powder diffraction and magnetic measurements. A minor impurity phase coexists with the main 1:7 phase in the as-cast compound NdCo7-xHfx with x=0.1 and 0.3. The compound with x=0.2 crystallizes in the TbCu7-type structure with the space group P6/mmm. According to the structure refinement, the doping element Hf prefers to occupy the 2e site. The phase stability of NdCo6.8Hf0.2 compound under different heat treatment conditions is also discussed. Thermomagnetic analysis shows that the NdCo6.8Hf0.2 compound has a Curie temperature of 1065K. The saturation magnetization of the NdCo6.8Hf0.2 compound is 113emu/g at 5K and 111emu/g at 300K. The compound exhibits a conical magnetic anisotropy at room temperature with a magnetic anisotropy field about 30kOe. In the NdCo6.8Hf0.2 compound, two spin reorientation transitions have been observed at 275 and 400K, respectively