Microscopic Magnetic Study on the Nominal Composition Li[Li1/3Mn5/3]O4 by Muon-Spin Rotation/Relaxation Measurements

Abstract

In order to elucidate the structural and physical properties of the nominal composition Li[Li1/3Mn5/3]O4 compound, we have investigated the nature of polycrystalline Li[LixMn2−x]O4 (LMO) with 0 ≤ x ≤ 1/3 and Li2MnO3 samples by electrochemical charge and discharge analysis, X-ray diffraction (XRD), magnetic susceptibility (χ), and muon-spin rotation/relaxation (μSR) measurements. Here, μSR signal roughly corresponds to the volume fraction of the local magnetic phases in the sample. The Rietveld analysis suggested that the x = 1/3 sample contains ∼11 weight% Li2MnO3 phase. This was also supported by electrochemical charge and discharge analysis and zero-field (ZF-) μSR measurements. If we follow the past reported relation for the x = 1/3 compound, i.e. Li[Li1/3Mn5/3]O4 consists of a (1 − z)Li[Li1/3−ωMn5/3+ω]O4 phase and a zLi2MnO3 phase, the average chemical formula of the former spinel phase is represented as Li[Li0.21Mn1.79]O4. However, weak-transverse-field μSR measurements demonstrated that the spinel phase undergoes a spin-glass-like transition at 21 K with a large transition width (ΔT = 28 K). Since both x = 0.2 and Li2MnO3 samples exhibit a very sharp magnetic transition at 24 and 36 K, respectively, the spinel phase in the x = 1/3 sample is found to be magnetically inhomogeneous in a microscopic scale. This indicates that the distribution of Li ions is microscopically inhomogeneous in the spinel lattice, although Li[Li1/3−ωMn5/3+ω]O4 has been assigned as a single-phase by macroscopic analyses such as XRD.