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

The affects of mixing samarium and gadolinium on the crystallographic and m agnetic properties of SmyGd2-yFe17-xSix (X = 0, 0.33, 0.67,1, 2, 3 and y = 0.33, 0.67, 1, 1.33, 1.67) intermetallics have been investigated using x-ra y diffraction techniques and SQUID and Vibrating Sample Magnetometer measur ements. The Sm-y Gd2-yFe17-xSi. samples, except for the sample with x = 3 a nd y = 1, crystallized in the rhombohedral Th2Zn17-structure with little or no impurities. For a given silicon content (fixed x), the unit cell volume and saturation magnetization increases at the approximate average rates of 4 Angstrom (3) and 24 emu/g per substituted samarium atom, respectively. T he 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 degr eesC per substitution. The affect of substituting silicon for iron on T-c i s more marked, with T-c increasing at a rate of almost 70 degreesC per sili con substitution at low silicon concentrations. For a given samarium conten t (fixed y), the unit cell volume and saturation magnetization decreases at approximate rates of 5 Angstrom (3) and 9 emu/g per substituted silicon at om, 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 lit tle magnetic anisotropy with no apparent dependence of the anisotropy on th e samarium or silicon content. The 340 degreesC T-c measured for the SmGdFe 14Si3 sample is unusually high for these intermetallics and its XRD pattern is indicative of a phase other than the rhombohedral Th2Zn17-type.