Investigation of the magnetic hyperfine field of¹¹¹Cd in the rare-earth Laves phases RCo₂and RNi₂

Abstract

The magnetic hyperfine field Bh f of the closed-shell probe nucleus 111 Cd on the cubic R site of the C15 Laves phase RCo2(R = Gd, Tb, Dy, Ho, Er, Sm, Nd and Pr) and RNi2(R = Gd, Sm) has been investigated at 9 K by perturbed angular correlation (PAC) spectroscopy. In RCo2the 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: Bh f = B3d - B4 f , where B3d is induced by the 3d Co moment and B4 f is due to indirect 4f - 4f exchange. The 4f contribution can be estimated from the measurement of Bh f in RNi2where the 3d moment vanishes. The 111 Cd hyperfine fields in GdNi2and SmNi2at 9 K are Bh f = 7.5(5) and 2.0(2) T, respectively. Assuming a linear dependence of B4 f on the projection ( g- 1)Jof the R spin on the total angular momentum J , as expected from the Ruderman-Kittel-Kasuya-Yosida (RKKY) theory of indirect 4f - 4f exchange, the variation of B3d across the R series can be determined from the experimental values of Bhf . In heavy RCo2(R = Gd, ... ,Er) B3d follows very closely the variation of the Co moment µCo across the R series with B3d /µCo = 28.7(2) T µ-1 B . With the same ratio for the light RCo2(R = Pr, Nd, Sm) the experimental Bh f values indicate an increase of the 3d moment from µCo = 0.45 to 0.7 µB between PrCo2and SmCo2 .