Preparation and magnetic properties of o-LiMnO2

Abstract

Pure o-LiMnO2 prepared by solid state reaction under Ar flow at 850 °C crystallizes in an orthorhombic symmetry (SG: Pmnm). Mn3+ with four unpaired electrons is subjected to a strong Jahn-Teller (J-T) distortion, where the MnO6 octahedron is significantly elongated (1.17%) along the c axis. In air, the oxide converts to spinel LiMn2O4 at ∼320 °C. The magnetic susceptibility of LiMnO2, measured between 4.2 and 900 K, indicates a long range order. The negative θP value (−790 K) reveals strong antiferromagnetic interactions between half-filled dz21 orbital. The predominant interaction is negative and occurs between Mn3+ and its next-nearest neighbors via O2− ions by super exchange with Mn3+-O: 2p-Mn3+ angle of 178°. Above 300 K, the susceptibility follows a Curie Weiss law with a magnetic moment of 5.26 μB consistent with the high spin state Mn3+ (t2g3 eg1) but slightly larger than the spin only contribution for the ground state 5Do. The susceptibility is field dependent down to 4.2 K and a spin canting has been detected at low temperature. As magnetic chains are separated by non-magnetic Li ones, the interactions are confined along the [1 1 0] direction and one can expect a good realization of one dimensional model. Therefore, the magnetic data have been fitted on the base of the isotropic model for finite linear chain in terms of intra-chain antiferromagnetic interactions using the Fisher model. The best fitting is obtained for a value of J/k = −60 K. The results are compared with those of the crednerite CuMnO2 with smaller J/k value (−33 K).