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 1.6K. Two modulation models, sinusoidal and helicoidal, give quite equivalent magnetic reliability factors (Rmag=0.0450 and 0.0481, respectively). The magnetic moment decreases with increasing temperature, to zero at TN=32K. The evolution of the propagation wave-vector shows an irregularity at about 28K. 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.