Perturbed angular correlation studies of 181Ta hyperfine interactions in Hf–Ni and Zr–Ni compounds

Abstract The hyperfine interaction experienced by 181 Ta nuclei in the intermetallic compounds ZrNi 5 , HfNi 5 , and Hf 2 Ni 7 has been investigated by perturbed angular correlation (PAC) spectroscopy. At temperatures T ≥15 K the 181 Ta angular correlation of appropriately annealed ZrNi 5 and HfNi 5 is unperturbed, indicating the absence of a magnetic hyperfine interaction. This observation rules out the possibility of spontaneous magnetic order of ZrNi 5 and HfNi 5 recently proposed in the literature. The temperature dependence of the electric quadrupole interaction of 181 Ta in Hf 2 Ni 7 suggests the existence of a reversible phase transformation at T ≥500 K.