Fabrication and Characterization of Chromium Oxide Nanoparticles/Thin Films
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Fabrication and Characterization of Chromium Oxide Nanoparticles/Thin Films Zhenchen Zhong Institute for Micromanufacturing (IfM) and Physics Program, Louisiana Tech University, Ruston, LA 71272; U.S.A. and Department of Physics, Grambling State University, Grambling, LA 71245, U.S.A. Ruihua Cheng Department of Physics and Astronomy and the Center for Materials Research and Analysis (CMRA), Behlen Laboratory of Physics, University of Nebraska-Lincoln, NE 68588-0111, U.S.A. ABSTRACT Well-dispersed nanoscale textured chromium oxide particles/thin films can be fabricated under certain conditions by laser-induced solution deposition (LISD) from organic solutions and by using selective organometallic chemical vapor deposition (OMCVD). The fabricated nanoparticles/thin films are characterized by scanning electron microscope (SEM), EDX, X-ray diffraction, and magnetic measurements. We have successfully demonstrated that the LISD and OMCVD are unique techniques for fabricating uniformly-distributed thin films but anistropic chromium oxide particles, which can be used in electro-magnetic devices. The magnetization measurements show that both types of chromium oxides are presented and that the Curie temperature Tc and the saturation magnetization field may be adjustable by controlling the stoichiometry. INTRODUCTION Spin-tunnel junctions, spin-vlaves [1] and other magnetoresistive devices [2,3] have aroused wide interests because of their importance in science and technology. These so-called spin-dependent devices, i.e., spintronics depend upon spin-polarized electrons rather than bias voltages or currents. They are new generation microelectronics, in other words, nanoelectronics. Chromium oxides are promising candidates because of their half-metallic properties and high spin-polarization. The insulating antiferromagnetic chromium oxide Cr2O3 has a Neél temperature TN (i.e., the similar Curie temperature for the antiferromagnetic case) 307 K and is suitable for tunnel junction barrier [3] both below and above the Neél temperature. The ferromagnetic chromium oxide CrO2 with Tc 397 K [4] has been predicted to be half-metallic (metallic for one spin direction while insulating for the other spin direction) by band structure calculations [5-9], though Kulatov and Mazin found CrO2 to be insulating in both spin-directions [10]. Evidence of 80 to 100% polarization, consistent with the half metallic character of CrO2, were observed in many experimental measurements such as spin-polarized photoemission [11], vacuum tunneling [12], and Andreev scattering [13,14]. The high electron polarization, in addition to the half metallic character of the surface [9] makes CrO2 an attractive material for spin-polarized electron tunneling. Very large spin-dependent tunneling (junction) magnetoresistance (TMR) made of CrO2 is expected. Therefore CrO2 is a material of interest for spin-polarized electronics (i.e., spintronics) because of the spin-polarization in this material approaching unity. Another reason for using CrO2 in spintronics is that it i
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