Neutron Diffraction Studies of Monoclinic Cr₃Te₄ Crystal

Monoclinic Cr₃Te₄ is known to exhibit ferromagnetic (FM) order below 320 K. Previous neutron diffraction studies performed on polycrystalline samples identified the appearance of weak antiferromagnetic (AFM) order below 85 K. Cr₃Te₄ crystals are grown by chemical vapor transport (CVT). Single crystal x-ray diffraction studies show a monoclinic phase (space group I2/m) with three distinct Cr occupancy sites and chemical formula Cr_2.90Te₄. Temperature-dependent neutron scattering studies on a crystalline sample of mass 23.7 mg are performed at HFIR/HB-1A to investigate the magnetic ordering in this material. Measurements are performed on a range of fundamental and superstructural Bragg peaks between 4 and 350 K. Rocking curves are consistent with three distinct domains, each with a different magnetic character and slightly different monoclinic angle. One appears to be uniquely associated with the FM order, which disappears above 327 K. A second exhibits peaks that double the unit cell, consistent with AFM order below 90 K. The third domain appears to show both FM and AFM responses. A plausible interpretation of these results is that the sample contains three distinct compositions, each with a slightly different Cr concentration, and that the magnetic order is quite sensitive to the composition.