LOW-TEMPERATURE MAGNETIC-BEHAVIOR OF CUFES2 FROM NEUTRON-DIFFRACTION DATA

Measurements of neutron diffraction spectra were made at temperatures 4.2, 25, 45, 65, 85, 150 and 300 K on powdered polycrystalline synthet ic CuFeS2. Standard Rietveld profile analysis using GSAS showed that a t all temperatures, a good fit to the data could be obtained with both the chemical and magnetic space groups taken as <I(4)over bar 2d>, an d an antiferromagnetic configuration of the Fe spins, as reported prev iously by Donnay et al. However, graphs of lattice parameters a and c against temperature showed a distinct change in slope close to 50 K, i ndicating the presence of a transition. Graphs of integrated intensity of diffraction lines against temperature showed corresponding discont inuities in the case of magnetic and mixed nuclear-magnetic lines but not for nuclear lines, indicating that the transition was magnetic, De tailed calculations of predicted magnetic intensities showed that the intensity variations could be explained by Cu spins, having a paramagn etic arrangement down to 50 K and then ordering to an antiferromagneti c form at lower temperatures. The analysis gave a value of similar to 0.05 mu(B), for the magnetic moment of the Cu ions.