Magnetic-field-induced spin crossover of Y-doped Pr0.7Ca0.3CoO3

The family of hole-doped Pr-based perovskite cobaltites, Pr0.5Ca0.5CoO3 and (Pr1−yREy)0.3Ca0.7CoO3 (where RE is rare earth), has recently been found to exhibit simultaneous metal-insulator, spin-state, and valence transitions. We have investigated magnetic-field-induced phase transitions of (Pr1−yYy)0.7Ca0.3CoO3 by means of magnetization measurements at 4.2–100 K up to an ultrahigh magnetic field of 140 T with the chemical pressure varied by y=0.0625, 0.075, 0.1. The observed magnetic-field-induced transitions were found to occur simultaneously with the metal-insulator transitions up to 100 T. The obtained magnetic-field-temperature (B−T) phase diagram and magnetization curves are well analyzed by a spin-crossover model of a single ion with interion interactions. On the other hand, the chemical pressure dependence of the experimentally obtained magnetization change during the phase transition disagrees with the single-ion model when approaching low temperatures. The significant y dependence of the magnetization change at low temperatures may arise from the itinerant magnetism of Co3+ in the paramagnetic metallic phase, where the chemical pressure enhances the exchange splitting by promoting the double-exchange interaction. The observed B−T phase diagrams of (Pr1−yYy)0.7Ca0.3CoO3 are quite contrary to that of LaCoO3, indicating that in (Pr1−yYy)0.7Ca0.3CoO3 the high-field phase possesses higher entropy than the low-field phase, whereas it is the other way around in LaCoO3