Browsing by Author "Kahsay Gebregziabher"

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    The inflllence of Cold Deformation on the Permeablity of Gases (H2,D2) in Metals (Ni, a- Fe)
    (Addis Ababa University, 1987-06) Kahsay Gebregziabher
    'I'll,; Ferr;-.l nvpru[lr.:i, ·'f rhe ('_!,:l.sc-ic /(~ner lilUdEi bas been cot'rec-ted and develop(~d for tlie ev,Llu.:~tlUd \)f tlH~ !..'l,_l:,t"ji: ("oulributiofl to the thermodYllamlr' chart:lctl~t"j--'-~tic:~ uf diffusion nnd ;-~nJqi:ton (li ~;U1l\f' intct":'3titial iHlpnritles (11,N.C) in bee metals (~--Fe). equatioH have. been cl-ltic':1.J ty .nn;11y?cd .c1.nd QP_veloped. A thcoLt"!tic31 det..crip-- t.lon of tll(:-~ gaHes pen.1H.:abLltt.y J.!lclltdfng both the diffus"lvity and solllhility Th:U-; theon~tic£l t dpSCJ~ipttOll h:l:;; h::~cn u.':.;ed I·.d::h respec.t to the KnO\oJl\ experilllental datil on I he in_rlu~~Hcl~ of pr-iur cold--d,-d!.)rmatlon on the gaBt!.8 (ll},D?) pCflIleahllit t\ model has been developed and i.n1pJr~ment~d lor ;"fudlng truc dJrru:-;ion c-oeftic.-ient1:: of .1.iflPU1-iti.es .tn the ne2f--rJ(slol'at:i.on -se,t;fegdtioH rl~Kloo:-;; (NDSR) in \'ihich tlH~rc ll:re 80[11(-' sU:lCnble eyper.:l.nwiltdl dZlt.a. Some infortnat.Jon OIl l:I'H? charach-,::_-i;~t tcs of tllP NlJSR has be(,;u obtained \·]hlch ShOHS that the NDSH. are not I!(~asy path H fOt: tmpurit.ie.s diffusion. A relev<1nL model of thr: >mSK structure has been discussed
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    Study of Coexistence of Superconductivity and Magnetism in Gd1+_Ba2−_Cu3O7−_ and UGe2 SUPERCONDUCTORS
    (Addis Ababa University, 2007-05) Kahsay Gebregziabher
    The coexistence of superconductivity and magnetism has recently re-emerged as a central topic in condensed matter physics due to the interplay between magnetism and superconductivity. The recent discovery of the coexistence of superconductivity( Sc) and antiferromagnetism(AFM) in high Tc superconductor(HTSc) Gd1+ Ba2− Cu3O7− has been studied theoretically by considering a model Hamiltonian consisting of pair interaction, intra and inter atomic Coulomb interactions, exchange interaction and scattering of Cooper pairs by magnetic moments of the gadolinium(Gd) ions. Using double time temperature dependent Green’s function formalism and a suitable decoupling approximation, the coexistence of superconductivity and antiferromagnetism has been demonstrated to be a distinct possibility in Gd1+ Ba2− Cu3O7− . The coexistence of superconductivity and ferromagnetism( Fm) in a ferromagnet UGe2 has also been shown theoretically by considering a model Hamiltonian and employing the Green’s function formalism. Furthermore, the variation of the Curie temperature(Tm) with pressure in UGe2 has been examined and investigated. The phase diagrams of the coexistence of superconductivity and magnetism in the above mentioned superconductors have been drawn which are in broad experimental agreement Keywords: Gd1+ Ba2− Cu3O7− , UGe2, coexistence of superconductivity and magnetism, superconducting order parameter, magnetic order parameter, antiferromagnetism, ferromagnetism, Ne’el temperature, Curie temperature, phase diagram.