Crystal and magnetic structure of Li2MnSiO4 and Li2CoSiO4 characterized by neutron diffraction measurement

Abstract

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.