Unusual magnetic phase transitions of TbNi5

In order to understand the nature of magnetic transitions in intermetallic TbNi5 compound, we have performed high resolution powder and single crystal neutron diffraction studies. Powder diffraction patterns can be described by a superposition of a ferromagnet (k1=0) and a transverse spin wave (k2{approximately equal to}2pi/c (,,0.018)). The single crystal experiments reveal two spontaneous magnetic transitions: one is a second-order transition at 24K from a paramagnetic state to an incommensurate structure and another a first-order transition at 10K from the incommensurate structure to a lock-in structure. At the low-temperature transition a large () thermal hysteresis is observed in the temperature dependence of the intensity of magnetic peaks. External magnetic fields destroy the modulated structure and induce a ferromagnetic state, which remains stable even after magnetic fields are switched off.