Spin State and Hyperfine Interaction in LaCoO3: NMR and Magnetic Susceptibility Studies

59 Co and 139 La NMR measurements have been performed to study the microscopic magnetic properties closely related with the spin state of a trivalent cobalt ion in LaCoO 3 . The temperature-independent 59 Co and 139 La Knight shifts below ∼ 30 K clearly revealed the presence of a nonmagnetic ground state at low temperatures. We calculated the temperature dependence of the magnetic susceptibility χ and the 59 Co Knight shift 59 K in a single ion model with the low-spin 1 A 1 ground state above which the high-spin 5 T 2 state is located. Then, both the trigonal crystal-field and spin-orbit interactions are taken into account. From this analysis, we infer the presence of an antiferromagnetic exchange interaction between the high-spin states. The characteristic temperature dependence of the 59 Co hyperfine coupling constant is also discussed.