On the nature of a new phase transition in α-MnS

Magnetic-susceptibility and X-ray-diffraction data of polycrystalline and oriented single crystal α-MnS reveal a new phase transition at T_tr = 131 K below the Néel temperature T_N = 148 K. The phase transition is characterized by an abrupt inversion of the rhombohedral distortion of the f.c.c. lattice along [111]. At T_tr there is a discontinuous change in the susceptibility of single crystals.