Micro- and macroscopic magnetism on layered cobalt dioxide LixCoO2 (0.1⩽x⩽1) Original Research Article

The magnetism for the electrochemically prepared LixCoO2 samples with 0.1⩽x⩽1 was investigated by muon-spin rotation/relaxation (μSR) and susceptibility (χ) measurements. The χ(T) curves with H=10 kOe, which correspond to the change in macroscopic magnetism, are almost T-independent down to ∼50 K for the x⩽0.44 samples, suggesting that the samples in this x range are Pauli-paramagnetic. For the samples with 0.49⩽x⩽3/4, a cusp is, however, observed around 170 K in their χ(T) curve. Since there are no anomalies in the μSR parameters around 170 K and μSR is sensitive to local magnetic nature, the cusp is most unlikely due to a magnetic transition, but either a spin state transition or a structural phase transition. Furthermore, zero-field μSR time spectra for all the samples mainly show a slow Kubo–Toyabe behavior, indicating that muon spin is mainly depolarized by randomly oriented nuclear moments of 7Li and 59Co. Hence, it was clarified that all the LixCoO2 samples with x<1 are paramagnetic even at 1.8 K, in contrast to NaxCoO2 and KxCoO2.