Effects of the doping element on crystal structure and magnetic properties of Sm(Co,M)7 compounds (M=Si, Cu, Ti, Zr, and Hf)

The crystal structure and magnetic properties of Sm(Co,M)7 (M=Si, Cu, Ti, Zr, and Hf) compounds with the TbCu7-type structure have been investigated by means of X-ray powder diffraction and magnetic measurements. For the Sm(Co,M)7 compounds, the formation of the compound is dominated by the enthalpy of formation of MCo7, atomic radius ratio of Sm to (Co, M) and the electronic configuration of the doping element M, while the site occupation of M is determined by the enthalpies of solution of M in liquid Sm and Co as well as by the electronegativity difference among M, Sm and Co. However, the Sm(Co,Cu)7 compounds exhibit different stabilizing mechanism, which may be due to the large mutual solubility between Co and Cu in the Sm(Co,Cu)7. The stabilizing element Si and Cu prefer to occupy the 3g site, whereas Ti, Zr and Hf have preference to occupy the 2e site. Both the saturation magnetization and Curie temperature of the Sm(Co,M)7 compounds decrease with increasing M content, while the magnetic anisotropy increases with increasing M content. The magnetic anisotropy field is related closely to the content and site occupation of the doping element M, which agrees with the theoretical analysis based on the individual site contribution model.