Structural and magnetic properties of the R 10 Fe 90-x Si x alloys with R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er

In this study alloys with stoichiometry of R2Fe17 and R10Fe90-xSix (x = 0, 10, 15, 20) (R = Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er) have been prepared. Structural transition from the ordered rhombohedral (OR) Th2Zn17-type structure and the ordered hexagonal (OH) Th2Ni17-type structure to their disordered structures (DR and DH) has been observed according to the XRD patterns. The lattice parameters were obtained by Rietveld analysis and based on the changing characteristic of the parameters, these samples are divided into two categories: alloys with R = Ce, Pr, Nd, Sm and alloys with R = Y, Gd, Td, Dy, Ho, Er. The lattice parameters of the two categories show different changing behavior. For example, from R2Fe17 to R10Fe90, the lattice parameters a decrease and c increase for the latter category, whereas for the former the lattice parameters a and c nearly have no change. In addition, increase of the ratio c/a has been found with increasing Fe or Si content, indicating the introduction of extra Fe dumbbells into the crystal cells, forming the DR or DH intermetallic compounds of R2-y(Fe,Si)17+2y. The obtained samples with disordered structure have shown better stability than the TbCu7-type metastable materials and the higher Fe concentration gives promise of higher magnetization. The mixed-rare-earth effect has also been studied in the (Ce,R)10Fe75Si15 alloys and transition between the DR and DH structures has been realized by changing the mixed R-type or adjusting the Ce/R ratio. As for the magnetic properties, the Curie temperatures are increased remarkably by the introduction of Si and the saturation magnetizations of R10Fe90-xSix are often higher than that of the R2Fe17 alloys.