Hyperfine fields in rare-earth compounds

Abstract

The hyperfine field at the cobalt nucleus in GdCo(_2), Gd(_1-x)Y(_x)co(_2), Gd(_1-x)Dy(_x)C0(_2), and Gd(Co(_1-x)Ni(_x))(_2) were studied using the technique of "Spin-Echo" N.M.R. At 4.2ºK cobalt has a negative hyperfine field of 60.8 Koe with a line width of 1.94 Koe. This field is composed of contributions from two main sources; a) from conduction electron (C,E.) polarization and core polarization of the cobalt electron configuration by the cobalt sub- lattice; b) from C.E. polarization of the cobalt electron configuration by the gadolinium sub-lattice. The spin of the gadolinium sub-lattice is decreased in the yttrium substituted series. This is accompanied by a slight decrease in the hyperfine field and a simultaneous increase in the line width of the resonance. An analysis of the variation in H(_c0), taking into account the induced change in cobalt sublattice magnetization, indicates that the contribution from the gadolinium sublattice is approximately 10 Koe per unpaired 4f electron. In addition, line width measurements show that the R.E. - T.M. interaction is long range in character. Magnetization measurements on the nickel substituted series show that the ToM, moment remains constant initially; indicating that the cobalt-nickel sublattice has an itinerant electron configuration. The variation in H(_CO) along this series is ascribed to a decrease in C.E, concentration with nickel substitution, A T,M, - T,M, interaction of short-range is indicated by the line width variation.