MAGNETIC-STRUCTURE OF CUO BY NEUTRON-DIFFRACTION WITH POLARIZATION ANALYSIS

Neutron diffraction with polarization analysis was performed on a single crystal of CuO, oriented with its a* and c* axes in the diffraction plane. It was verified that in the commensurate phase I (0-212.7 K; k = (1/2 , 0, -1/2)), the magnetic moments were indeed along b*, but it was found that in the incommensurate phase II (212.7-232.5 K; k = (0.506,0, -0.483)) there also exists a component of the magnetic moment along b* in disagreement with an earlier study by Forsyth et at. Our data are in agreement with the very recent results of Brown et al. We propose a helimagnetic arrangement in the incommensurate phase II, with the magnetic moments rotating in the plane (b*; 0.506a* + 1.517c*). We present here a short account of our experimental results, a study of thc stability of thc magnetic structure in phase II and the symmetry analysis of the possible magnetic space groups.