Diffuse Paramagnetic Neutron Scattering in Chromium Spinels

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Abstract
This paper describes an investigation of the diffuse neutron diffraction attributable to the paramagnetic state in normal, cubic spinels. The elastic neutron scattering is calculated from the high‐temperature expansion of the correlation function 〈Si·Sj〉 as a power series in inverse temperature, the pertinent coefficients being evaluated elsewhere for a Heisenberg Hamiltonian with both nearest‐neighbor A‐B and B‐B interactions. After normalization to the nuclear diffraction pattern, the computed diffuse scattering is compared with the experimental findings for both MnCr2O4 and MnCr2S4. Good agreement exists in both cases, despite the striking qualitative difference between these two patterns. This agreement supports the calculational model, and thereby answers earlier speculation concerning the origin of the liquid‐type diffraction peaks observed in the room‐temperature diffraction patterns of most chromium spinels. It is shown that these peaks are not directly related to any spin canting in the ground state. They arise from the basic antiferromagnetic nature of the exchange interactions, would persist in the absence of any B‐B exchange, and can be suppressed by sufficiently strong ferromagnetic B‐B interactions, as evidenced in MnCr2S4.

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