Magnetic structures of βI-Li2CoSiO4 and γ0-Li2MnSiO4: crystal structure type vs. magnetic topology

Abstract

The magnetic structure and properties of the candidate lithium-ion battery cathode materials Pbn21(≡Pna21) Li2CoSiO4 and P21/n Li2MnSiO4 have been studied experimentally using low-temperature neutron powder diffraction and magnetometry. Both materials undergo long-range antiferromagnetic ordering, at 14 K and 12 K respectively, due to super-super-exchange mediated by bridging silicate groups. Despite having different crystal structures (wurtzite- vs. “dipolar”-type), Li2CoSiO4 and Li2MnSiO4 have the same topology in terms of magnetic interactions, and adopt collinear magnetic structures of the same type with the propagation vectors (0,1/2,1/2) and (1/2,0,1/2) respectively. The magnetic moments in the two materials are aligned perpendicular-ly and obliquely to the distorted closed-packed layers of oxygen atoms. The experimentally observed values of the ordered magnetic moments, 2.9 μB and 4.6 μB, are close to those expected for d7 Co2+ and d5 Mn2+ re-spectively.