Transition Metal Doped ZnO for Spintronics
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Transition Metal Doped ZnO for Spintronics S. J. Pearton1, D. P. Norton1, M. P. Ivill1, A. F. Hebard2, W. M. Chen3, I. A. Buyanova3 , and J. M.Zavada4 1 Materials Science and Engineering, Univ.Florida, Gainesville, FL, 32611 2 Physics, Univ.Florida, Gainesville, FL, 32611 3 Physics, Linkoping University, Linkoping, Sweden 4 Electronics Division, Army Research Office, Research Triangle Park, NC, 27709 ABSTRACT ZnO is a very promising material for spintronics applications, with many groups reporting room temperature ferromagnetism in films doped with transition metals during growth or by ion implantation. In films doped with Mn during PLD, we find an inverse correlation between magnetization and electron density as controlled by Sn doping. The saturation magnetization and coercivity of the implanted single-phase films were both strong functions of the initial anneal temperature, suggesting that carrier concentration alone cannot account for the magnetic properties of ZnO:Mn and factors such as crystalline quality and residual defects play a role. Plausible mechanisms for the ferromagnetism include the bound magnetic polaron model or exchange is mediated by carriers in a spin-spilt impurity band derived from extended donor orbitals. Spindependent phenomena in ZnO may lead to devices with new or enhanced functionality, such as polarized solid-state light sources and sensitive biological and chemical sensors. INTRODUCTION The use of carrier spin, in addition to charge, appears promising for a new class of devices such as polarized light emitters, chips that integrate memory and microprocessor functions , magnetic devices exhibiting gain and ultra-low power transistors (1-10). The use of carrier spin in metallic multilayers forms the basis of hard drives in information storage. The control of spin-dependent phenomena in electronic oxides or more conventional semiconductors may lead to devices such as spin light-emitting diodes(spinLEDs) ,spin field effect transistors (spin-FETs) and the spin qubits for quantum computers (1,2,8) .A key requirement in realizing most devices based on spins in solids is that the host material be ferromagnetic above room temperature. In addition, it is necessary to have both efficient spin-polarized carrier injection and transport. It is generally believed that it is necessary to achieve single-phase dilute magnetic oxides in order to realize useful devices, since it is the polarized carrier population that carries the spin information, although there may be applications for multi-phase materials in magneto-optical applications. The usefulness of ferromagnetic semiconductors for spintronic applications requires the existence of a coupling between ferromagnetic and semiconducting properties, independent of the actual microstructure of the system under study. If precipitates or clusters below detectable size limits are present and responsible for the ferromagnetism and if the carriers do not mediate the ferromagnetic interaction, then the usfulness of such materials in spintronics s
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