A MOSSBAUER-EFFECT INVESTIGATION OF SITE PREFERENCES AND FE ENVIRONMENTS IN GA-SUBSTITUTED SM2FE17 COMPOUNDS

Room temperature Fe-57 Mossbauer studies of the 2:17 compounds Sm2Fe17 -xGax with x=0, 1, 2, 3, 4 and 5 are reported. These measurements yiel d values of the Fe hyperfine field and relative concentration of Fe at oms at the four inequivalent transition metal sites, 6c, 9d, 18f and 1 8h, in the rhombohedral Th2Zn17 structure. Changes in the Fe hyperfine field as a function of Ga content can be correlated to changes in lat tice parameter and Curie temperature and are the result of changes in the transition metal-transition metal exchange coupling. The relative intensity of the various spectra components shows that for small conce ntrations, Ga preferentially enters into the 18h sites. For x>1 a subs tantial quantity of Ga also enters into the 18f sites. It is the Ga wh ich enters into the 18f sites which is responsible for the formation o f a uniaxial anisotropy in these materials for higher Ga content. (C) 1997 Elsevier Science S.A.