Investigation of the magnetic hyperfine field of Cd-111 in the rare-earth Laves phases RCo2 and RNi2

摘要

The magnetic hyperfine field B-hf of the closed-shell probe nucleus Cd-111 on the cubic R site of the C15 Laves phase RCo2 (R = Gd, Tb, Dy, Ho, Er, Sm, Nd and Pr) and RNi2 (P = Gd, Sm) has been investigated at 9 K by perturbed angular correlation (PAC) spectroscopy. In RCo2 the hyperfine field increases with increasing R spin, both for the heavy and the light R. The experimental trend suggests that the total hyperfine field has two contributions of opposite sign: B-hf = B-3d - B-4f, where B-3d is induced by the 3d Co moment and B-4f is due to indirect 4f-4f exchange. The 4f contribution can be estimated from the measurement of B-hf in RNi2 where the 3d moment vanishes. The Cd-111 hyperfine fields in GdNi2 and SmNi2 at 9 K are B-hf = 7.5(5) and 2.0(2) T, respectively. Assuming a Linear dependence of B-4f on the projection (g - 1)J of the R spin on the total angular momentum J, as expected from the Ruderman-Kittel-Kasuya-Yosida (PICKY) theory of indirect 4f-4f exchange, the variation of B-3d across the R series can be determined from the experimental values of B-hf. In heavy RCo2 (R = Gd,. . .,Er) B-3d follows very closely the variation of the Co moment mu(Co) across the R series with B-3d/mu(Co) = 28.7(2)T mu(B)(-1) With the same ratio for the light RCo2 (R = Pr, Nd, Sm) the experimental B-hf values indicate an increase of the 3d moment from mu(Co) = 0.45 to 0.7 mu(B) between PrCo2 and SmCo2. [References: 28]