Neutron Diffraction and Mössbauer Study of Ordered and Disordered LiFeO2

Abstract

Neutron diffraction and Mössbauer studies of two crystallographic forms of LiFe${\mathrm{O}}_2$ have been made. The ordered tetragonal form, in which there is cation order similar to that in CuFe${\mathrm{S}}_2$, becomes antiferromagnetic below 315°K. Good neutron intensity agreement is obtained with a collinear spin structure in which there is strong antiferromagnetic superexchange between ${\mathrm{Fe}}^{3+}$ ions in (001) planes, but only weak coupling between the planes. The moments are directed along the [001] axis and the magnetic symmetry is tetragonal. Identical calculated intensities are given by a second collinear structure of lower symmetry in which ferromagnetic (111) planes of moments are coupled antiparallel, but the x-ray data are not consistent with this model. However, this type of structure is realized in disordered, cubis LiFe${\mathrm{O}}_2$ below 90°K, although both the neutron scattering and the Mössbauer spectra reveal that the long-range magnetic order is far from complete.