Magnetic and Diffusive Nature of LiFePO4

In order to elucidate the magnetism and Li diffusion in LiFePO4, we have measured muon-spin rotation and relaxation (μ+SR) spectra for a polycrystalline LiFePO4 sample in the temperature range between 1.8 and 500 K. Below TN ∼ 52 K, two oscillatory signals together with onefast relaxation signal were clearly found in the zero-field (ZF) μ+SR spectrum. The three signals are reasonably explained using an antiferromagnetic (AF) spin structure proposedby neutron measurements, because electrostatic potential calculations suggests multiple different muon sites in the LiFePO4 lattice. However, the AF ordered moment estimated from μ+SR was about 3/4 of that reported by neutron, probably due to a different time window between the two techniques. In the paramagnetic state, ZF-and longitudinal-field (LF-) μ+SR spectraexhibiteda dynamic nuclear field relaxation. From the temperature dependence of the field fluctuation rate, a diffusion coeffcient of Li+ ions (DLi) at300K was estimated about 3.6×10−10 cm2/s, assuming that diffusing Li+ ions jump between the regular site and interstitial sites.