The Magnetic Hyperfine Field of 111 Cd in the Rare EarthYNickel Laves Phases RNi 2 S. MU ¨ LLER, P. DE LA PRESA and M. FORKER* Helmholtz Institut fu ¨r Strahlen- und Kernphysik der Universita ¨t Bonn, Nussallee 14-16, D-53115 Bonn, Germany; e-mail: forker@iskp.uni-bonn.de Abstract. The magnetic hyperfine field of 111 Cd in the C15 Laves phases RNi 2 has been investigated by perturbed angular correlation (PAC) spectroscopy as a function of temperature for the rare earth constituents R = Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm. 1. Introduction The rare earth (R) Y nickel intermetallic compounds RNi 2 present a C15 superstructure (space group F-43m) in which the 4a sites of the R sublattice are only partially occupied. The concentration of R vacancies decreases from a few percent for R = Pr to zero for R = Lu [1, 2] We have recently shown by a 111 Cd perturbed angular correlation (PAC) study [3] that these vacancies are highly mobile at room temperature and that for R = Pr, Nd, Sm and Gd they can be trapped by the PAC probe 111 Cd. Although 111 Cd resides on the cubic R site of the C15 structure, in some of the paramagnetic RNi 2 111 Cd is therefore subject to an axially symmetric quadrupole interaction (QI) produced by the trapped vacancies. In the present contribution we report an extension of these 111 Cd PAC studies to the magnetically ordered phases of RNi 2 . 2. Measurements The PAC measurements were carried out with the 171Y245 keV cascade of 111 Cd between 4.2 K and 290 K. The compounds RNi 2 with R = Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm were produced by arc melting of the metallic components with the stoichiometry ratio 1 : 2 in an argon atmosphere. The samples, characterized by X-ray diffraction, were doped with 111 Cd by diffusion (800-C, 12 h) of carrier-free radioactive 111 In into the host lattice. Figure 1 shows typical spectra of 111 Cd in RNi 2 observed at 290 K and 4.2 K. In the case of the heavy R constituents R = Tb, Dy, Ho, Er and Tm, the angular * Author for correspondence. Hyperfine Interactions (2004) 158:163–167 DOI 10.1007/s10751-005-9031-5 # Springer 2005