Unveiled magnetic transition in Na battery material: μ+SR study of P2-Na0.5VO2

We have investigated the microscopic magnetic nature of a novel Na battery material, P2-Na0.5VO2, in which V ions form a two-dimensional triangular lattice, by means of muon-spin rotation and relaxation (mu+SR) measurements down to 50 mK. Although magnetization measurements indicated the presence of an antiferromagnetic transition at 13 K, the internal magnetic field due to the formation of magnetic order appears not at 13 K but at 2 K. Furthermore, the magnetic order is found to have a wide field distribution even at 50 mK. Such wide field distribution is reasonably explained by a combination of multiple muon sites and the formation of a long-range magnetic order, while the reliable spin structure is still unknown.