Crystal and magnetic structure of Li₂MnSiO₄ and Li₂COSiO₄ characterized by neutron diffraction measurement

Full text: Lithium orthosilicates compounds Li₂MnSiO₄ and Li₂CoSiO₄ were synthesized by solid state reaction and characterized using X-ray powder diffraction, magnetic susceptibility measurement, heat capacity and neutron powder diffraction. The magnetic susceptibility measurement shows that Li₂MnSiO₄ and Li₂CoSiO₄ obey Curie Weiss behaviour at high temperature and undergo antiferromagnetic ordering below TN = ~12 K and ~13 K respectively. The magnetic structures of both compound have been solved for the first time using low temperature neutron diffraction data. The results reveal that the magnetic structure of Li₂CoSiO₄ can be described as antiferromagnetic quasi-layers stacked along the a-axis with the magnetic moment ~2.92 μB aligned parallel to the a-axis. The magnetic structure of Li₂MnSiO₄ showed quite different behaviour compared to Li₂CoSiO₄. The origin of this complex magnetic structures will be discussed in terms of super-superexchange interactions among the transition metal ions, mediated by bridging SiO₄ tetrahedra. (author)