Spin and temperature dependence of the magnetic hyperfine field of 111Cd in the rare earth-aluminum Lavesphase compounds RAl2

Perturbed angular correlation spectroscopy has been used to investigate the combined magnetic and electric hyperfine interaction of the probe nucleus Cd-111 in ferromagnetically ordered rare earth (R)-dialuminides RAl2 as a function of temperature for the rare earth constituents R = Pr, Nd, Sm, Eu, Tb, Dy, Ho and Er. In compounds with two magnetically non-equivalent Al sites (R = Sm, Tb, Ho, Er), the magnetic hyperfine field was found to be strongly anisotropic. This anisotropy is much greater than the anisotropic dipolar fields, suggesting a contribution of the anisotropic 4f-electron density to magnetic hyperfine field at the closed-shell probe nucleus. The spin dependence of the magnetic hyperfine field reflects a decrease of the effective exchange parameter of the indirect coupling with increasing R atomic number. For the compounds with the R constituents R = Pr, Nd, Tb, Dy and Ho the parameters B-4, B-6 of the interaction of the crystal field interaction have been determined from the temperature dependence of the magnetic hyperfine field. The Cd-111 PAC spectrum of EuAl2 at 9 K confirms the antiferromagnetic structure of this compound. (C) 2006 Elsevier B.V. All rights reserved.