Browsing by Author "Mesele, Degefa"

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    Signi_Cance of Hole-Magnon Interaction on Ferromagnetism in Diluted Magnetic Semiconductors
    (Addis Ababa University, 2018-05-02) Mesele, Degefa; Amente, Chernet (PhD)
    In this thesis we studied hole-magnon dynamics to understand the contribution of their interaction on the enhancement of ferromagnetism in diluted magnetic semiconductors (DMS). The t-J model is used as the interaction Hamiltonian with a method of per- turbation mathematical approach in which canonical transformation is used to obtain convergent values starting with canting the quantum anti-ferromagnetism from its Neel state by some angle _ with respect to the z-axis. Employing a spinless fermion represen- tation for hole operators, Holstein-Primako_ and Bogoliubou transformations are used to change the hole and spin dynamics to the many body problem. Our calculations in- dicated that motion of a hole in the anti-ferromagnetic background is dependent on the magnetic correlation of the system and the tilted angle. The motion of a hole around the anti-ferromagnetic order is shown to be characterized by high and low energy dispersion uctuation as the angle changes from 00 to 900. This uctuation in energy spectrum is attributed as arising from the pair repair spin alignment which could happen in anti- ferromagnetic(AF) background because of the hole motion e_ect. This is to mean that the motion of the hole causes a disturbance on the spin cloud of the localized electrons. This also infer that e_ect of hole motion gives a ferromagnetic (FM) order (maxima) and anti-ferromagnetic (AF) order (minima) uctuation. Making use of the obtained result, energy dispersion (Ek), spectral function (density function) (Ak) and quasiparticle weight (Zk) for the t=J << 1 and t=J >> 1 limit were numerically evaluated and plotted.