Phase Transitions of SrFeO$_{3}$ Studied Using a Single-Crystalline Film

To study the electronic nature of SrFeO$_{3}$ (SFO), which is a cubic perovskite containing Fe$^{4+}$ equipped with deep $d$ levels and is, therefore, dominated by $p$-hole character, a single crystalline film was grown and the resistivity (\textit{$\rho $}), Hall effect, magnetoresistance (\textit{MR}) and susceptibility were measured. It is known that this oxide in bulk form becomes antiferromagnetically ordered in a screw spin structure. The $T_{N}$ of the film has been found to be at 120$\sim $125 K from the susceptibility measurement, while the transport properties showed well-defined anomalies at 105 K, rather than at the $T_{N}$. The metallic film (\textit{$\rho $} = 9$\times $10$^{-4} \quad \Omega $cm at 300 K) exhibited a hysteretic, inflectional drop in the \textit{$\rho $} -$T $curve at 105 K after showing a very small anomaly at 125 K; the Hall coefficient was positive and temperature-independent above 110 K but increased quickly below $\sim $100 K; the \textit{MR} changed its sign from negative to positive quite steeply at 105 K. Considering these results together with what is known about bulk samples, we conclude that SFO undergoes its antiferromagnetic transition in two stages, passing an incompletely coherent stage before entering the final coherent state.