MOSSBAUER STUDY OF THE HYPERFINE INTERACTION OF FE-57 IN Y1-SCO5-COMPOUNDS(2S AND RELATED)

The magnetic and electric hyperfine interaction and the relative fract ions of dilute Fe-57 nuclei on the four Co sites of Y1-sCo5+2s have be en investigated by Mossbauer spectroscopy as a function of the relativ e number s of Y atoms substituted by Co dumbbells. We also report Moss bauer measurements of Fe-57 in GdCo5, SmCo5, and Sm2Co17(rh). The s de pendence of the relative Mossbauer fractions of Fe-57:Y1-sCo5+2s, toge ther with previous neutron diffraction results, allows an experimental site-hyperfine field assignment. The Fe atoms strongly favor the dumb bell sites at the expense of sites 6l of the hexagon surrounding the C o pair, while sites 2c and 3g are randomly occupied. In stoichiometric RCo5 (R=Y, Sm, Gd) we observe a sizable dumbbell concentration, which is probably caused by the precipitation of R2Co17 favored by the impu rity nature of the Mossbauer probe. With the increasing number of near est Co neighbors, the magnetic hyperfine field passes from site 3g thr ough a minimum at site 2c towards the maximum H-hf=31.5 T at the dumbb ell site. The 4f contribution to the magnetic hyperfine field is. smal l; the changes upon substitution of Y by R = Gd, Sm are of the order o f 10%.