Surface physical property of the CrO 2 thin films prepared using a closed chemical vapor deposition method
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Surface physical property of the CrO2 thin films prepared using a closed chemical vapor deposition method Y. Muraoka1,2, S. Yoshida1, T. Wakita1, M. Hirai1,2, T. Yokoya1,2 1
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Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan Faculty of Science, Research Laboratory for Surface Science, Okayama University, 3-1-1 Tsushima-naka, Tsushima, Kita-ku, Okayama 700-8530, Japan
ABSTRACT We have examined the intrinsic surface physical property of a CrO2 thin film by means of surface sensitive photoemission spectroscopy. Epitaxial thin film of CrO2(100) has been grown on TiO2(100) by a closed chemical vapor deposition method using a Cr8O21 precursor. Lowenergy electron diffraction (LEED) observations find that epitaxial growth of rutile-phase CrO2 occurs to the top monolayer of the film. Surface sensitive x-ray photoemission spectroscopy (XPS) measurements show a finite intensity in the region of the Fermi energy. The result evidences that the physical nature of near topmost layer of CrO2 thin film is metallic. Progress of understanding of the surface physical property of CrO2 thin film helps not only perform a reliable photoemission study to understand the physics of ferromagnetic metal in CrO2, but also develop the CrO2-based devices using a half-metallic nature for spintronics applications. INTRODUCTION Chromium dioxide CrO2 is a ferromagnetic metal with a Curie temperature TC of about 400 K. This is interesting in itself because metallic and ferromagnetic behaviors are rarely found together for 3d transition metal oxides: most oxides exhibit strong insulating and antiferromagnetic characteristics. Motivated by the unique characteristics, intensive experimental and theoretical works have been devoted to understanding the physics of CrO2. So far, it is considered that the double exchange interaction between localized Cr 3d electrons via intermediate oxygens plays a crucial role for the simultaneous occurrence of metallic behavior and ferromagnetism [1,2]. CrO2 has also attracted considerable attention because it is a halfmetallic band structure fully spin-polarized at the Fermi level [3]. Several classes of materials are predicted to have this half-metallic ferromagnetic property, including the Heusler alloys and magnetites Fe3O4. Of all of the half-metallic ferromagnetic materials, CrO2 is presently the only material with experimentally proven spin polarization close to 100 % as measured Andreev reflection [4,5]. These results are motivation to use this material in spintronics devices such as magnetic field sensing and information storage. It has long been desired to perform a reliable XPS study in order to understand the physics of CrO2. It has also been required to prepare a high-quality interface to develop the
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CrO2-based devices using a half-metallic nature for spintronics applications. Both for fundamental and application studies, it is crucial to obtain the metallic surface of CrO2. CrO2 is a metastable phase at ambient conditions. It h
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