On the Mechanism of the Spin State Transition of (Pr_1−ySm_y)_1−xCa_xCoO₃

Abstract

Transport, thermal, and magnetic measurements have been carried out on (Pr_1−ySm_y)_1−xCa_xCoO₃. The system exhibits a structural phase transition accompanied by the spin state change from the intermediate spin (IS) state to the low spin (LS) state with decreasing temperature T. We have constructed a T–y phase diagram for x=0.3 and T–x ones for y=0.2 and 0.3. By analyzing their magnetic susceptibilities, the number of Co ions excited to the IS state (or the electron number in the e_g orbitals), n_IS, is roughly estimated. With increasing y or with decreasing x, n_IS decreases, and the phase transition changes gradually to the (IS→LS) crossover-like one. We discuss the possible role of the Pr atoms in realizing the transition.