Direct measurement of the low temperature spin state transitions in La_1−xSr_xCoO₃ (0.05 < x < 0.3)

Sr-doped LaCoO₃ has a complex magnetic phase diagram, which is believed to be directly correlated to changes in the crystal structure and ordering of the Co³⁺ spin states. In this work, we study the low temperature Co³⁺-ion spin state transitions in Sr-doped LaCoO₃ around the critical doping concentration where a metal to insulator transition has been observed using electron energy-loss spectroscopy of the O K-edge combined with the Co L-edge fine structure. We measure the local spin state of the Co³⁺-ions and we demonstrate that the Co³⁺ spin-state transition only occurs in La_0.95Sr_0.05CoO₃ single-crystal materials in the temperature range accessible by LN₂ in-situ cooling, while no structural symmetry change is observed. The presence of this low-temperature spin-state transition in La_1−xSr_xCoO₃ (x < 0.17) has been proposed as the origin of the percolative magnetic ordering in doped LaCoO₃.