Nanocrystals and thin films of oxide and chalcogenide spinels for spintronic applications
Spin-based transport in semiconductor systems has been proposed as the foundation of a new class of spintronic devices. For the practical realization of such devices it is important to identify magnetic materials with diverse electronic transport properties (metallic, semiconducting, insulating) and sufficiently high Curie temperature (T_C ) that can be readily integrated with standard semiconductors. Promising classes of materials for this purpose are the magnetic spinel oxides and chalcogenides. Some of these spinel-based materials are also attractive for biomedical applications. The facile solution-based synthesis of monodisperse nanocrystals of a wide variety of magnetic ferrites and nanocrystals of the chalcospinel CuCr_2 Se_4 , along with their structural and magnetic properties, is presented in the first section of the dissertation. The following section presents a theoretical investigation of the electronic band structure of two quaternary chalcospinel systems, Cd_x Cu_1-x Cr_2 Se_4 and Cd_x Cu_1-x Cr_2 S_4 , and also a number of anion-substituted Cr-based chalcospinels. A wide range of half-metal compositions are predicted both for the cation and anion substituted chalcospinels. The synthesis of spinels has been expanded to the growth of ferrites films using the direct liquid injection chemical vapor deposition (DLI-CVD) technique, which is detailed in the last section of the dissertation. High quality epitaxial NiFe_2 O_4 films have been grown using this technique with the magnetic properties of the films being comparable to those observed in the bulk, even for films grown at a high deposition rate. The growth of other thin film ferrites, such as lithium ferrite and barium hexaferrite, which are useful for higher frequency microwave applications are being investigated. The eventual goal is to use extend the DLI-CVD technique for the synthesis of chalcospinels films - in particular those predicted to be half-metallic - which have the potential for a variety of applications in spintronic devices.