Revealing magnetic ground state of a layered cathode material by muon spin relaxation and neutron scattering experiments

Abstract

Although the majority of studies on battery materials have focused on enhancing their electrochemical performance, the understanding of their magnetic and atomic structures as well as the intimate connections between these structures and properties is significant. Muon spin relaxation (μSR) spectroscopy and neutron scattering techniques at low temperature have been used to explore the nature of the magnetic state of Li(Ni0.4Mn0.4Co0.2)O2 cathode materials. Interestingly, the μSR experiment reveals that the spins of Ni/Mn/Co ions turn glassy at a low temperature of 19 K, while the unprecedented spin dynamics survives until the base temperature of 5.6 K. Moreover, the complementary neutron scattering measurements show magnetic diffuse scattering signals in the form of a broad peak at Q = 1.6 Å-1 attributed to short-range spin correlation which establishes below ∼120 K. Upon cooling to as low as 480 mK, long-range magnetic order still could not be established. The inelastic neutron scattering intensities demonstrate clearly the existence of dynamic spin fluctuations. In contrast to the conventional spin glass system, the coexistence of both dynamic and static components in the ground state suggests an unconventional spin glass state in magnetically frustrated Li(Ni0.4Mn0.4Co0.2)O2 cathode materials for Li-ion batteries.