A neutron diffraction and Mouml;ssbauer spectral study of the structure and magnetic properties of the Y2Fe14minus;xSixB solid solutions

摘要

A neutron diffraction and Mouml;ssbauer spectral study of Y2Fe14minus;xSixB shows that silicon preferentially occupies the 4c, and to a lesser extent, the 8j1sites in Y2Fe14minus;xSixB. The trend in the site occupancy is the same as in Nd2Fe14minus;xSixB. The Curie temperature of Y2Fe14minus;xSixB increases with increasing silicon content. Neutron diffraction data show that the increase in Curie temperature is accompanied by a contraction of the unit cell. Wignerndash;Seitz cell calculations, using the Y2Fe14minus;xSixB lattice and positional parameters obtained by neutron diffraction, show that the silicon site occupancy is correlated with the rare earth contact area of that site. The Mouml;ssbauer spectra of Y2Fe14minus;xSixB have been fit with a model which takes into account the distribution of nearhyphen;neighbor environments of an iron atom due to the presence of silicon. The weighted average ofHmax, the average hyperfine field of the iron sites with no silicon near neighbors, decreases by 42 and 45 kOe per silicon substitution per formula unit at 85 and 295 K, respectively. The weighted average of Dgr;H, the average reduction in the hyperfine field caused by the addition of one silicon near neighbor to the near neighbor environment, is about 13.5 and 18 kOe at 85 and 295 K, respectively, and does not show an appreciable dependence on the silicon content. The isomer shifts obtained from these fits suggest an increase in covalency of bonding on silicon substitution, an increase which is consistent with the preference of silicon to bond with yttrium.