title: Metallic ferromagnet with square-lattice CoO2 sheets.
abstract: A single-crystalline film of Sr2CoO4 with square-lattice CoO2 sheets (K2NiF4-type structure) was synthesized, and its electronic properties were characterized. The compound exhibited both ferromagnetic and metallic behaviors, with a fairly high Curie temperature T(C) of approximately 250 K, in contrast to the superconductivity recently found in a triangular-lattice CoO2-sheet compound. The film's large magnetoresistance with current perpendicular to the CoO2 plane showed field-hysteretic behavior analogous to tunneling magnetoresistance. The electronic structure of Sr2CoO4 was also investigated to characterize the quasi-two-dimensional ferromagnetic metal state in terms of optical spectroscopy and first-principles calculation.
authors.affiliation: Correlated Electron Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8562, Japan. j-matsuno@aist.go.jp
authors.forename: J
authors.initials: J
authors.lastname: Matsuno
authors.forename: Y
authors.initials: Y
authors.lastname: Okimoto
authors.forename: Z
authors.initials: Z
authors.lastname: Fang
authors.forename: X Z
authors.initials: XZ
authors.lastname: Yu
authors.forename: Y
authors.initials: Y
authors.lastname: Matsui
authors.forename: N
authors.initials: N
authors.lastname: Nagaosa
authors.forename: M
authors.initials: M
authors.lastname: Kawasaki
authors.forename: Y
authors.initials: Y
authors.lastname: Tokura