Electrical and Magnetic Properties of Doped ZnO Nanowires
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Electrical and Magnetic Properties of Doped ZnO Nanowires Gennady N. Panin1,2, Andrey N. Baranov3, Tae Won Kang1, Oleg V. Kononenko2, Sergey V. Dubonos2, S. K. Min4, and H. J. Kim4 1 QSRC, Department of Physics, Dongguk University, 3-26 Pil-dong, Chung-gu, Seoul, 100-715, Korea, Republic of 2 Inst. of Microelectronics Technology, RAS, Chernogolovka, Moscow distr., 142432, Russian Federation 3 Department of Chemistry, Moscow State University, Moscow, 119992, Russian Federation 4 Department of Semiconductors, Dongguk University, Seoul, 100-715, Korea, Republic of
ABSTRACT ZnO nanowires doped with Mn, Fe, Sn, and Li during the thermal growth following direct chemical synthesis were investigated using electric and magnetic measurements. Currentvoltage characteristics of individual nanowires configured as a two-terminal device with Al electrodes show apparent rectify behavior indicating the Schottky-like barrier formation and resistivity being less 3 Ω·cm. Reproducible resistance modulation by a dc voltage at room temperature is observed. Magnetic susceptibility of the doped nanowires as a function of temperature demonstrates Curie–Weiss behavior. Magnetization versus field curves show hysteresis with the coercive field of about 200 Oe. The spatially-resolved magnetic force measurements of individual nanowires revealed the magnetic domain structure. The domains align perpendicular to c-axis and can be polarized in the external magnetic field. INTRODUCTION Zinc oxide is one of the most important functional semiconductor oxide with a direct wide band gap (3.37 eV) and a large exciton binding energy (60 meV) [1]. ZnO-based nano scale materials such as nanowires have attracted enormous interest due to its unique combination of electric, piezoelectric and optical properties. In recent years, attention has focused on spindependent phenomena in dilute magnetic zinc oxide in which stoichiometric fraction of the zinc atoms are replaced by transition metal (TM) impurities. The typical dopants that induce magnetic properties in the ZnO-based semiconductors are Mn, Fe and Co, which have been usually used with additional codopants supplying free carriers. In spite of theoretical predictions of room temperature ferromagnetism originated by carrier-induced interaction between TM atoms in ZnO, the experimental results have been strongly contradictory. Ferromagnetism in the oxide material remains poorly understood experimentally. ZnO:Co (3) and ZnO:Mn (2,3) DMSs films were found to be paramagnetic, while others reported ferromagnetism in ZnO:Co (4,5) and ZnO:Mn (10-12). High-Tc ferromagnetism attributed to ZnO:Mn DMS films was suggested to appear due to phase-segregation [8]. Several recent studies on ZnO:Mn, ZnO:Co and ZnO:Fe showed that ferromagnetism depends strongly on methods and conditions used in the preparation [4,6,9]. Magnetic ordering in ZnO-based DMS appears sensitive to point defects such as vacancies [5,10] which can supply electrons (holes) and can effect considerably on both magnetic and electric properties.
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