Search for Spontaneous Magnetic Order in ZrNi5 and HfNi5

The hyperfine interaction experienced by 181Ta nuclei in the intermetallic compounds ZrNi5, HfNi5 and Hf2Ni7 has been investigated by perturbed angular correlation (PAC) measurements, in a temperature range 15 K ≥ T ≤ 1,200K. The temperature dependence of the electric quadrupole interaction of 181Ta in Hf2Ni7 suggests the existence of a reversible phase transformation at T ≥ 500 K.