  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$^{4+}$).
