Field Induced Spin-State Transition in LaCoO3

The magnetization of LaCoO 3 shows a magnetic transition induced by level crossing at a magnetic field of 60 T below 25 K, which is consistent with the energy diagram determined from electron spin resonance experiments. However, the amount of Co ions with g = 3.35 contributing to the magnetic transition is sample-dependent and at most 14% of the total Co ions in LaCoO 3 . We found that the rest of the Co ions also contribute to the magnetization, which is a maximum at around 100 K. We analyzed the magnetization assuming two kinds of Co species, Co I and Co II , both of which have the nonmagnetic ground state. The energies and the g values of the magnetic excited states are 135 K and 3.35 for Co I , and 250–260 K and 1.9–2.0 for Co II , respectively. Co I ions are suggested to be associated with oxygen vacancies and the surface of LaCoO 3 .