1998 年 67 巻 1 号 p. 290-296
Neutron-diffraction measurements have revealeda new anomalous thermal lattice expansion of LaCoO3 near 500 K thatindicates the existence of a second spin-state transition, in addition to theone previously established near 100 K. The anomalous expansion and thetemperature dependence of the Co magnetic moments are successfullyinterpreted in a wide temperature range based on a simple model assuminglow-spin (LS, S=0), intermediate-spin (IS, S=1), and high-spin(HS, S=2) states of Co atoms.The first spin transition, near 100 K, is from LS to IS, andthe second, near 500 K, is from IS to a mixed state of IS and HS.The fitted model parameters indicate that the initially-large energy differencebetween IS and HS states decreases towards zero as the secondtransition proceeds. The large drop in resistivity associated with the lattertransition appears to be correlated with the population of the HS state.
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