Tuning Magnetic Symmetry and Properties in the Olivine Series Li_1–xFe_xMn_1–xPO₄ through Selective Delithiation

We present the first in-depth study of the nuclear and magnetic structures of the fully lithiated LiFexMn1–xPO4 solid solutions as well as the partially delithiated Li1–xFexMn1–xPO4 series using neutron powder diffraction. By using a weak oxidizing solution that only oxidizes Fe2+, we find that lithium can be removed from these olivines in a stepwise manner. Representational analysis was performed on the observed magnetic reflections and found that the lithiated solid solutions order in the magnetic space group Pnma′, which is identical to triphylite (LiFePO4). We report that, even when removing 20% of the lithium from the hcp lattice, the magnetic structure changes and multiple magnetic contributions are needed to fully encompass the observed magnetic order. We find that the partially delithiated x = 0.2 and 0.3 have a magnetic structure P21′/n11, and when x surpasses 0.3, the magnetic structure changes to P212121. We give a detailed report on the effect of delithiation on magnetic order, bond distances/angles, and the super- and supersuperexchange interactions in the material. The symmetries of the magnetic order of these solid solutions are then discussed with regard to their potential as ferrotoroidic candidates.