A Powder Neutron Diffraction Study of Structure and Magnetism in NiCr₂S₄

Powder neutron diffraction data for NiCr₂S₄have been collected over the temperature range 1.8=T=286 K. The Cr₃S₄structure (space groupI2/m) is adopted at all temperatures. Refinement of 286 K data (a=5.8954(14) Å,b=3.4066(8) Å,c=11.0589(22) Å,ß=91.362(4)°) demonstrates that the distribution of nickel and chromium cations between sites in a fully occupied metal layer and sites in an ordered vacancy layer is close to that expected for the normal structure type. Data collected at 1.8 K (a=5.8621(5) Å,b=3.4051(2) Å,c=11.0297(9) Å,ß=91.607(6)°) reveal the presence of long-range magnetic order, involving a doubling of the unit cell in both theaandcdirections. Cations in the fully occupied metal layer possess an ordered magnetic moment of 1.57(6)µ_Bwhich is directed parallel to the cation layers. Cations in the vacancy layer have a moment of 1.36(8)µ_Bwhich is directed toward the anion layers. The magnetic ordering temperature was determined as 180(5) K. These results are correlated with magnetic susceptibility and electrical conductivity data. © 1997 Academic Press.