Effect of iron-doping on spin-state transition and ferromagnetism in Pr${}_{0.5}$Ca${}_{0.5}$CoO${}_{3-\delta }$ cobalt oxides

Abstract

Resistivity and dc magnetization measurements were performed for the polycrystalline Pr${}_{0.5}$Ca${}_{0.5}$Co${}_{1-x}$Fe${}_x$O${}_{3-\delta }$ ($x$ = 0, 0.05, 0.10 and 0.15) samples. The as-fabricated samples exhibit ferromagnetic (FM) transition and the transition temperature increases with increasing the iron doping level. Annealing under high oxygen pressure induces a spin-state transition of Co ions in the \emph{iron-free} sample and such transition is reinforced with increasing the annealing oxygen pressure, while the annealing under high oxygen pressure suppresses the ferromagnetic ordering. Contrary to the case of the \emph{iron-free} sample, no spin-state transition is induced by the annealing under high oxygen pressure for the \emph{iron-doped} samples, and the ferromagnetic transition temperature is nearly independent of the annealing procedures. The enhancement of the spin-state transition in the \emph{iron-free} sample after annealing under high oxygen pressure should be attributed to the reduction of the cell volume. The suppression of the spin-state transition by the Fe doping is related to the enlargement of the cell volume and the stronger Fe-O bonds than Co-O bonds. The enhancement of the ferromagnetism by the iron-doping might arise from the ferromagnetic exchange interaction between Fe${}^{3+}$ and Co${}^{4+}$ through oxygen (Fe${}^{3+}$-O-Co${}^{4+}$).

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