Low energy nuclear spin excitations in HoAl2 investigated by high resolution neutron spectroscopy

We have investigated low energy excitations in metallic HoAl2 by high resolution neutron spectroscopy. At T=3 K we found clear inelastic peaks in the energy loss and energy gain sides along with the central elastic peak. We interpret these inelastic peaks to be due to the transitions from hyperfine-split nuclear levels. The energy which is E = 25.03 ± 0.02 μ eV at T=3 K, decreases continuously and becomes zero at T N ≈ 30 K . The intensity of the inelastic peak remains more or less constant as a function temperature before the it merges with the central elastic peak at TN. The energy of nuclear spin excitations in HoAl2 seems to follow the order parameter of the ferromagnetic phase transition.