Abstract
We report powder and single-crystal neutron diffraction measurements, combined with x-ray powder diffraction data, to unravel the complex magnetic phase diagram and exchange coupling in CoTeO. The magnetic structures of the various phases differ markedly from those proposed by Ivanov et al. [Mater. Res. Bull. 47, 63 (2012)] on the basis of only powder diffraction data. The dominant exchange interactions are identified by considering the geometrical arrangement of severely distorted CoO octahedra and CoO tetrahedra, which naturally divide into two different types of layers, one of which consists of zigzag chains. These zigzag chains are the first to develop magnetic order at 26 K, which is incommensurate in nature. The other separate layer of Co spins develops antiferromagnetic order of symmetry at zero wave vector at 19.5 K. Our results are consistent with the previous findings of a spontaneous polarization below 18 K. Our neutron powder diffraction data indicate that the increase in the single-crystal (600) Bragg peak is due to a relief of extinction rather than to magnetic effects associated with the observed anomalous variation in the incommensurate wave vector at 16 K. The commensurate order parameter is shown to have a small dependence on the applied electric field, whereas no such effect is found for the incommensurate ordering. Below , the thermal expansion is negative, and it also exhibits anomalies at and . A symmetry analysis and comprehensive phase diagram are given.
4 More- Received 12 January 2013
DOI:https://doi.org/10.1103/PhysRevB.88.184427
©2013 American Physical Society