Magnetic phase transition in single crystals of the chiral helimagnet Cr_1/3NbS₂

The chiral helimagnet Cr_1/3NbS₂ has been investigated by magnetic, transport, and thermal properties measurements on single crystals and by first-principles electronic structure calculations. From the measured field and temperature dependence of the magnetization for fields applied perpendicular to the c axis, the magnetic phase diagram has been constructed in the vicinity of the phase transition. A transition from a paramagnetic to a magnetically ordered phase occurs near 120 K. The transition is found to strongly affect the electrical transport. The resistivity decreases sharply upon cooling near 120 K, and the spin reorientation from the helimagnetic ground state to the commensurate ferromagnetic state is evident in the magnetoresistance. At high fields, a large magnetoresistance (55% at 140 kOe) is observed near the magnetic transition temperature. Heat capacity and electronic structure calculations show that the density of states at the Fermi level is low in the magnetically ordered state.