MAGNETIC-ORDERING OF THE ANTIFERROMAGNET CU2MNSNS4 FROM MAGNETIZATIONAND NEUTRON-SCATTERING MEASUREMENTS

Magnetization and neutron-diffraction measurements were performed on a single crystal of Cu2MnSnS4. This quartenary magnetic semiconductor h as the stannite structure (derived from the zinc-blende structure whic h is common to many II-VI dilute magnetic semiconductors), and it orde rs antiferromagnetically at low temperature. The neutron data for the nuclear structure confirm that the space group is I<(42)over bar>m. Bo th the neutron and magnetization data give T-N = 8.8 K for the Neel te mperature. The neutron data show a collinear antiferromagnetic (AF) st ructure with a propagation vector k = [1/2, 0, 1/2], in agreement with earlier neutron data on a powder. However, the deduced angle theta be tween 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 th e spin axis is indeed close to the c direction. The deduced magnetic a nisotropy gives an anisotropy field H-A congruent to 2 kOe. At high ma gnetic fields the magnetization curve at T much less than T-N shows th e 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 antiferrom agnetic interactions are an order of magnitude smaller than in II-VI d ilute magnetic semiconductors (DMS's). The much weaker antiferromagnet ic interactions are expected from the difference in the crystal struct ures (stannite versus zincblende). A more surprising result is that th e exchange constant which controls the AF order below T-N is not betwe en Mn ions with the smallest separation. This result contrasts with a prediction made for the related II-VI DMS, according to which the exch ange constants decrease rapidly with distance.