Browsing by Author "Senbeta, Teshome"

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    2D Spin-Dependent Electron Scattering by Nanomagnets
    (Addis Ababa University, 2012-02) Senbeta, Teshome
    The 2D scattering problem of an electron by a magnetized nanoparticle is solved in the Born approximation with account of the dipole - dipole interaction of the magnetic moments of electron and nanomagnet. The scattering amplitudes in this problem are the two-component spinors. They are obtained as functions of the electron spin orientation, the electron energy and show anisotropy in scattering angle. The initially polarized beam of electrons scattered by nanomagnet consists of electrons with no spin flipped and spin flipped. The majority of electrons with no spin flipped are scattered by small angles. This can be used as one method of controlling spin currents. 2D spin-dependent scattering of slow unpolarized beams of electrons by charged nanomagnets is analyzed in the Born approximation. The obtained scattering lengths are larger than those from the neutral nanomagnets approximately by one order. It is shown that for particular parameters of the system it is possible to polarize completely the scattered electrons in a narrow range of scattering angles. The most suitable system for realization of these effects is 2D Si electron gas with immersed nanomagnets. The 2D spin-dependent electron scattering by the linear chain of periodic nanomagnets with account of the diffraction effects was studied. This effect takes place in 2D electron gas with immersed nanomagnets. By tuning a distance between nanomagnets, it is possible to obtain diffraction maximum of the scattered electrons at scattering angle, which corresponds to complete spin polarization of electrons. The total diffraction scattering lengths are proportional to N2 (N is a number of nanomagnets). The proposed system can be an efficient separator of spin polarized currents
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    Temperature-Dependent,; Hyperfine Interaction at the 111CD Nucleus in Silicon
    (Addis Ababa University, 2005-06) Senbeta, Teshome; Tessema, Genene (PhD)
    Impurity atoms (indium and tellurium ) were incorporated in silicon through an implantation process. The samples were annealed to remove radiation damage. The formation of Cd-Te complex and the temperature dependence of the quadrupole interaction frequency ( QIF) were studied with help of perturbed 7 — 7 angular correlation ( PAC) technique. The observed pairing between Cd and Te was due to the interaction between acceptors and donor atoms in silicon. This explains how the presence of Te influences the lattice site of the Cd atoms. The unique quadrupole interaction frequency UQ = 444M H z was associated to this complex formation. The strong quadrupole interaction frequency, 444MHz at room temperature, decreases to 388MHz at 7U 0°C' which is associated to the state (