Neutron Scattering Study of ZnCr₂Se₄ with Screw Spin Structure

Neutron scattering experiments have been carried out on a single crystal and powdered specimens of ZnCr₂Se₄, a helimagnet, above and below the transition at T_N=21.2 K. Below T_N, crystal belongs to D¹⁹_4h. Atomic parameters of Se can be expressed by a single parameter, «=0.3847. Rather small magnetic moment (1.71 μ_B at 0 K) and the linear dependence of the length of the screw vector, Q₀, on the lattice deformation were observed. Anisotropic critical scattering (J_x/J_y≅3) was measured around (4 — Q₀, 0, 0) above T_N and Q dependence of the exchange interaction constant, J(Q), near Q₀ was discussed. Recent studies by Plumier et al. were critically referred.