Novel metallic ferromagnet Sr2CoO4

We report on synthesis and electronic characterization of single-crystalline film of Sr2CoO4 with square-lattice CoO2 sheets (K2NiF4-type structure). In this compound, we have found both ferromagnetic and metallic behaviors with fairly high Curie temperature TC of ∼250 K, as contrasted by the superconductivity recently found in a triangular-lattice CoO2-sheet compound. The electronic structure of Sr2CoO4 was also investigated in terms of in situ photoemission spectroscopy.