Spin state ordering of strongly correlating LaCoO3 induced at ultrahigh magnetic fields

Magnetization measurements of LaCoO3 have been carried out up to 133 T, generated with a destructive pulse magnet at a wide temperature range from 2 to 120 K. A novel magnetic transition was found at B > 100 T and T > T* = 32 +/- 5 K, which is characterized by its transition field increasing with increasing temperature. At T < T*, the previously reported transition at B similar to 65 T was observed. Based on the obtained B-T phase diagram and the Clausius-Clapeyron relation, the entropy of the high-field phase at 80 K is found to be smaller for about 1.5 J K-1 mol(-1) than that of the low-field phase. We suggest that the observed two high-field phases may originate in different spatial orders of the spin states and possibly other degrees of freedom such as orbitals. An inherent strong correlation of spin states among cobalt sites should have triggered the emergence of the ordered phases in LaCoO3 at high magnetic fields.