Neutron diffraction study of magnetic ordering of the manganese bismuth chloro-sulfide: MnBiS2Cl

In quaternary compounds of Mn²⁺PnQ₂X (Pn = Sb, Bi; Q = S, Se; X = Cl, Br, I), Mn atoms in octahedral coordination (4 Q and 2 X) form waved layers separated by Pn atoms. The magnetic structure of the manganese bismuth chloro-sulfide MnBiS₂Cl has been determined by neutron powder diffraction, revealing a magnetic ordering with an incommensurate wave-vector along b-axis (k = [0, 0.3978, 0]) at 1.6 K. Two modulation models, sinusoidal and helicoidal, give quite equivalent magnetic reliability factors (R_mag = 0.0450 and 0.0481, respectively). The magnetic moment decreases with increasing temperature, to zero at T_N = 32 K. The evolution of the propagation wave-vector shows an irregularity at about 28 K. It could evidence two-phase transitions in agreement with the specific heat measurements. These results are compared to those of manganese antimony chloro-sulfide MnSbS₂Cl, isotypic with MnBiS₂Cl.