Magnetic properties of highly resistive BaFeO3 thin films epitaxially grown on SrTiO3 single-crystal substrates

We have synthesized single-crystalline films of ${\mathrm{BaFeO}}_3$ (BFO), which may contain unusual tetravalent Fe ions, on (100) and (111) ${\mathrm{SrTiO}}_3$ substrates by pulsed laser-beam deposition. The epitaxially grown BFO is considered to have a pseudocubic perovskite-type crystal structure with some oxygen vacancies. The films were found to be highly insulating, and showed a high value of dielectric constant of $\text{ε=59.}$ The magnetization curve of the films exhibited hysteresis, as well as small remanent magnetization. The origin of the observed small magnetization can be ascribed to the mixed valence state of the ${\mathrm{Fe}}^{\text{4+}}$ and ${\mathrm{Fe}}^{\text{3+}}$ ions. The present epitaxially grown BFO apparently had some different magnetic and dielectric properties from those for bulk BFO as well as for the previously reported other ${\mathrm{Fe}}^{\text{4+}}$ oxides: coexisting high resistivity and spontaneous magnetization at room temperature.