Structure and magnetism of the Sm7.5Y2.5Fe90−xSix (x=0.0, 2.5, 5.0, 7.5 and 10) alloys

Sm7.5Y2.5Fe90−xSix (x=0.0, 2.5, 5.0, 7.5 and 10) alloys have been prepared by arc melting method and equilibrium disordered Th2Zn17-type phases, (Sm,Y)2−y(Fe,Si)17+2y, with relative lower rare-earth content than the ordered Th2Zn17-type phase, have been obtained. Compared to the ordered Th2Zn17-type structure, the X-ray diffraction (XRD) intensity of the superstructure lines of the (Sm,Y)2−y(Fe,Si)17+2y decreases with the increase of the Si content and becomes zero for x=10. According to the refinement with the disordered Th2Zn17-type structure, the occupation rates of the R atoms at (3a) and (6c) sites tend to reach the same value with the increase of the Si content, and the lattice parameter a decreases while the lattice parameter c increases, leading to an increase of c/a. It was found that the atomic ratio of Fe(Si)/Sm(Y) in the disordered Th2Zn17-type structure increases with the increase of Si content and reaches a maximum value of 9.07 with x=10. The XRD diagrams of the magnetic aligned samples indicate that the easy magnetization direction (EMD) of the (Sm,Y)2−y(Fe,Si)17+2y is in the a-b plane, and the change of the EMD in a-b plane has also been observed due to the Si preferred site occupation. The remanence ratios along the easy direction are higher than that along hard direction; however, all the remanence ratios are less than 0.5. The magnetocrystalline anisotropy constant K increases first and then decreases with increasing the Si content. The Curie temperature of Sm7.5Y2.5Fe90−xSix alloys increases by about 65 K per Si. The saturation magnetization increases first and then decreases with a maximum of 135.5 emu/g observed for x=2.5 at room temperature.