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

The hyperfine interaction experienced by 181Ta nuclei in the intermetallic compounds ZrNi5, HfNi5, and Hf2Ni7 has been investigated by perturbed angular correlation (PAC) spectroscopy. At temperatures T≥15 K the 181Ta angular correlation of appropriately annealed ZrNi5 and HfNi5 is unperturbed, indicating the absence of a magnetic hyperfine interaction. This observation rules out the possibility of spontaneous magnetic order of ZrNi5 and HfNi5 recently proposed in the literature. The temperature dependence of the electric quadrupole interaction of 181Ta in Hf2Ni7 suggests the existence of a reversible phase transformation at T≥500 K.