Mixed rare-earth effects in (Sm/Gd)2(Fe/Si)17 intermetallics

The effects of mixing samarium and gadolinium on the crystallographic and magnetic properties of Sm_yGd_2-y Fe_17-xSi_x (x=0, 0.33, 1.67) intermetallics have been investigated using X-ray diffraction techniques and SQUID and vibrating magnetometer measurements. The Sm_yGd_2-yFe_17-xSi_x samples, except for the sample with x=3 and y=1, crystallized in the rhombohedral Th₂Zn₁₇-structure with little or no impurities. For a given silicon content (fixed x), the unit volume and saturation magnetization increases at the approximate average rates of 4 Å ³ and 24 emu/g per substituted samarium atom, respectively. The Curie temperature (T_c) for a given silicon content, on the other hand, decreases with increasing samarium content at an average rate of 30-40°C per substitution. The affect of substituting silicon for iron on T_c is more marked, with T_c increasing at a rate of almost 70°C per silicon substitution at low silicon concentrations. For a given samarium content (fixed y), the unit cell volume and saturation magnetization decreases at approximate rates of 5 ų and 9 emu/g per substituted silicon atom, respectively. X-ray diffraction studies of magnetically aligned powders indicate that the easy direction of magnetization is in the basal plane of the rhombohedral unit cell. All of the samples were found to have very little magnetic anisotropy with no apparent dependence of the anisotropy on the samarium or silicon content. The 340°C T_c measured for the SmGdFe₁₄Si₃ sample is unusually high for these intermetallics and its XRD pattern is indicative of a phase other than the rhombohedral Th₂Zn₁₇-type