Magnetic phase transitions in TbNi$_5$ single crystal: bulk properties and neutron diffraction studiesw

The magnetic susceptibility, heat capacity and neutron diffraction measurements have been carried out in order to study the unusual magnetic ordering of TbNi$_5$ using a single crystal over the temperature region of 2$\sim$30 K. Two spontaneous magnetic transitions have been observed: one is a second order transition from a paramagnetic state to an incommensurate structure ($T_p=24$ K) and the other a first order transition from the incommensurate structure to a lock-in phase ($T^c_f=10$ K). We also found an irreversible magnetic field-induced transition from the modulated structure to the ferromagnetic collinear one.