Application of a layered triangular-lattice magnetic model system toLiNiO2

The magnetic susceptibility of ${\mathrm{LiNiO}}_2$ can be described by a high-temperature Curie-Weiss law that is typical of ferromagnets but without spontaneous magnetization at low temperatures. We find that some of the ESR features of ${\mathrm{LiNiO}}_2$ below 40 K which were earlier attributed to a quantum spin-liquid state are present at higher temperatures around 240 K in ${\mathrm{Li}}_{0.3}$ ${\mathrm{Ni}}_{0.7}$O. This behavior is typical of superparamagnetic domains. The magnitude of the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ NMR anisotropic paramagnetic dipolar shift in ${\mathrm{La}}_2$ ${\mathrm{Li}}_{0.5}$ ${\mathrm{Ni}}_{0.5}$ ${\mathrm{O}}_4$ and ${\mathrm{LiNiO}}_2$ suggests that the moment is localized predominantly on Ni ions. Arguments are presented to suggest that the systematics are consistent with the predominant creation of holes on Ni on the substitution of Ni by Li in NiO. The same conclusion is drawn from the ESR studies.