Magnetic and magneto-transport properties in nanostructured materials

Magneto-transport, magnetic and structural properties of three nanostructured systems: (1) single-crystal bismuth films with and without antidot arrays made by electrodeposition, (2) epitaxial half-metallic CrO₂ films made by chemical vapor deposition (CVD), and (3) exchange-coupled Co/FeMn/permalloy trilayers prepared by magnetron sputtering are presented.; Single-crystal Bi thin films have been made by electrodeposition followed by suitable annealing. X-ray diffraction verifies that the films are trigonal axis oriented single-crystal films. High resolution transmission electron microscope reveals the expected six-fold symmetry of the atomic structure of Bi(001) films. These films exhibit very large magnetoresistance (MR) at both low temperature and room temperature, as well as strong anisotropy among the perpendicular, transverse, and longitudinal geometries. At very low temperature, the MR of Bi films shows Shubnikov-de Haas oscillations, further confirming the high quality of the films. Bi films with ordered antidot arrays patterned by optical lithography exhibit pronounced angular dependence in magnetoresistance, in agreement with theoretical calculations.; X-ray diffraction studies of epitaxial CrO₂ films, made by CVD on TiO₂(100) substrates demonstrate single-crystal quality of the films. These films exhibit a strong uniaxial magnetocrystalline anisotropy with a unique switching behavior, which can be described by a simple model. Critical behavior of the CrO₂ films, determined by magnetometry with the magnetic field along the uniaxial anisotropy axis, indicates that CrO₂ is a Heisenberg ferromagnet with long-range interaction.; Trilayers of permalloy/FeMn/Co with various thicknesses t _AF of the antiferromagnetic FeMn layer prepared by magnetron sputtering have been designed to reveal the spin structure within FeMn. A spiraling spin structure has been observed in such trilayers.