Development of a Novel Metal Epitaxy Method Towards Ni Based Electro-Magnetic Hybrid Systems
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0962-P09-04
Development of a Novel Metal Epitaxy Method Towards Ni Based Electro-Magnetic Hybrid Systems Akifumi Matsuda1, Masayasu Kasahara1, Takahiro Watanabe1, Wakana Hara1, Sei Otaka1, Kouji Koyama2, and Mamoru Yoshimoto1 1 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259-R3-6 Nagatsuta, Midori, Yokohama, 226-8503, Japan 2 Crystal Growth Laboratory, Namiki Precision Jewel Co., Ltd., 3-8-22 Shinden, Adachi, Tokyo, 123-8511, Japan
ABSTRACT A novel epitaxy method obtains epitaxial Ni (111) thin film on the oxide substrates. This method uses pulsed-laser deposition (PLD) of NiO (111) epitaxial film on sapphire (α-Al2O3 single crystal) substrates and successive hydrogen reduction of NiO. The NiO (111) epitaxial film was deposited on the sapphire (0001) substrate at room temperature by pulsed-laser deposition and then reduced into the Ni epitaxial film by annealing (300 °C to 500 °C) in a hydrogen-atmosphere. Polycrystalline Ni metal thin film was obtained by reduction of the polycrystalline NiO film, indicating necessity of epitaxial growth for the precursor oxide thin film in the metal epitaxy. The present epitaxy method suggests the possible formation of an [Ni/α-Al2O3] epitaxial multilayer via selective reduction of oxide multilayers. INTRODUCTION Spin-controlled electronic devices, composed of nanoscale-integrated structures with ferromagnetic metal and nonmagnetic (or insulative) material, have attracted much interest. These so-called spintronics devices utilize not only the charge of electrons, but also their spin degree of freedom for ferromagnetic materials that may lead to spin-dependent electronic transport [1–3]. Various possible applications have been proposed, such as magnetic random access memory (MRAM) or spin transistors, spin filters, spin modulators and quantum information devices that could be implemented in active control of spin dynamics. In the spintronics field, single crystalline or epitaxial phases of ferromagnetic material with nanometerscale controlled structures are desirable, as opposed to materials in an amorphous or randomoriented polycrystalline state, because of the decisive influence of crystallographic anisotropy on the magnetic properties [4]. For example, ferromagnetic Ni epitaxial films have been largely produced directly from a pure metallic source by thermal evaporation [5], electron-beam evaporation [6], molecular-beam epitaxy (MBE) [7, 8], sputtering [5, 8] and pulsed-laser deposition (PLD) [4, 9], or by wet processes such as electro deposition using toxic sulfate solution [10]. There have been few studies on the formation of epitaxial Ni thin films by reduction of oxide thin films. A few studies reported of formation of thin layers of Ni (100) by reducing a surface of the bulky single crystal NiO using hydrogen gas or ultrahigh vacuum [11].
The development of this novel epitaxial technique for ferromagnetic metal films using a combination of oxide epitaxy and reduction, is expected to open a new field of spintronics. A variety of met
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