Magnetic Properties of MnCr2S4

The neutron diffraction pattern of MnCr₂S₄ at room temperature shows it to be a normal cubic spinel. The magnetization of this material was measured from 4.2° K through the Curie temperature. It was then determined, on the basis of a molecular field calculation, that the shape of the magnetization curve requires a large and ferromagnetic B‐B interaction such that J_BB/J_AB∼−4. This is in general accord with Lotgering's conclusion, which was based on paramagnetic susceptibility data, and indicates that the material should have a simple Néel (collinear) spin configuration. This expectation was confirmed by a 4.2°K neutron diffraction investigation which also established the cation moments to be 3μ_B per chromium ion and 4.7μ_B per manganese ion, in agreement with the measured net magnetization of 1.3μ_B. Furthermore, the 4.2°K diffraction pattern clearly indicates that the reduction of the manganese moment below its spin‐only value cannot be attributed to A‐site canting. On the basis of the above results, we are forced unequivocally to the conclusion that the tetrahedrally coordinated Mn²⁺ cannot be in a pure ${}^6{S}_{\frac{5}{2}}$ state.