Distinguishing the Intrinsic Antiferromagnetism in Polycrystalline LiCoPO 4 and LiMnPO 4 Olivines

We report a detailed investigation of the long-range magnetic ordering in polycrystalline samples of LiCoPO and LiMnPO , which belong to a series of well-known olivine cathode materials Li PO (M = Mn, Fe, Co, Ni). Samples were prepared by hydrothermal and solid state methods. The magnetic susceptibility is found to be strongly field-dependent, impacting the antiferromagnetic transition temperature and the bifurcation of the FC and ZFC curves. We discuss the role synthesis conditions have on impurity formation and particle size. We report neutron powder diffraction data for the samples prepared by solid state methods. Based upon representational analysis of the observed reflections, we affirm the magnetic structure ' for LiCoPO and ' ' ' for LiMnPO . The refined magnetic moments from these models are 3.28(4) μ for LiCoPO and 4.28(3) μ for LiMnPO . We also study the onset of magnetic ordering in each sample and affirm that the ordering temperature is 22 K for LiCoPO and 34 K for LiMnPO . The critical parameters describing those transitions are β = 0.21(4) (LiCoPO ) and β = 0.31(3) (LiMnPO ). These values are characteristic of a 3D Ising system for LiMnPO and intermediate behavior between a 2D and 3D Ising system for LiCoPO . We compare these observations with other reports proposing lower magnetic symmetry.