Magnetic ordering of the antiferromagnet Cu2MnSnS4 from magnetization and neutron-scattering measurements

Magnetization and neutron-diffraction measurements were performed on a single crystal of Cu2MnSnS4. This quartenary magnetic semiconductor has the stannite structure (derived from the zinc-blende structure which is common to many II-VI dilute magnetic semiconductors), and it orders antiferromagnetically at low temperature. The neutron data for the nuclear structure confirm that the space group is I<(42)over bar>m. Both the neutron and magnetization data give T-N = 8.8 K for the Neel temperature. The neutron data show a collinear antiferromagnetic (AF) structure with a propagation vector k = [1/2, 0, 1/2], in agreement with earlier neutron data on a powder. However, the deduced angle theta between the spin axis and the crystallographic c direction is between 6 degrees and 16 degrees, in contrast to the earlier value of 40 degrees. The magnetization curve at T much less than T-N, shows the presence of a spin rotation (analogous to a spin flop), which indicates that the spin axis is indeed close to the c direction. The deduced magnetic anisotropy gives an anisotropy field H-A congruent to 2 kOe. At high magnetic fields the magnetization curve at T much less than T-N shows the transition between the canted (spin-flop) phase and the paramagnetic phase. The transition held, H = 245.5 kOe, yields an intersublattice exchange field H-E = 124 kOe. The exchange constants deduced from H-E and the Curie-Weiss temperature Theta = -25 K shaw that the antiferromagnetic interactions are an order of magnitude smaller than in II-VI dilute magnetic semiconductors (DMS's). The much weaker antiferromagnetic interactions are expected from the difference in the crystal structures (stannite versus zincblende). A more surprising result is that the exchange constant which controls the AF order below T-N is not between Mn ions with the smallest separation. This result contrasts with a prediction made for the related II-VI DMS, according to which the exchange constants decrease rapidly with distance.