1.مطالعه ابتدا به ساكن سطح ﴿001﴾ Co2FeSi و مرز مشترك ﴿001﴾ Co2FeSi/GaAs و 2. توصيف توپولوژيكي پيوند و مغناطيس در تركيبات﴿XAs(X=V ، Cr ، Mn ،Fe ،Co

چكيده انگليسي :

143 1 First principle study of Co2FeSi 001 surface and Co2FeSi GaAs 001 interface 2 Topological Description Of Bonding and Magnetism In Zinc Blende XAs X V Cr Mn Fe Co Shekoufeh Khosravizadeh shekoufe khosravi@gmail com 31 July 2011 Department of Physics Isfahan University of Technology 84156 83111 Isfahan IranHadi Akbarzadeh akbarzad@cc iut ac irS Javad Hashemifar hashemifar@ cc iut ac irAbstractIn this project we performed a first principle study of some half metals which are of importance inspintronics All of the calculations are in density functional theory DFT frame work depending on therequirements of the problem in different arts of the project we applied one of two computational code PWscf or WIEN2k WIEN2kis an all electron LAPW computational code while calculation in PWscf isbased on pseudo potential method and using plane waves as basis set for wave functions Initially wehave performed an overview on DFT In this part we did especial focus on LDA U to improve on sitecorrection have been applied in some part of this project The first part of the project is assigned to thestudy of bulk properties of Co2FeSi alloy and its interface with GaAs 001 substrate Co2FeSi belongs toheusler alloys for which half metallic character is expected At first a overview on bulk properties was performed In this study it was found that in the case of thisalloy improving the onsite correlation using LDA U is relevant so that half metallic character that islost in GGA within GGA U is seen for this alloy Hence for remaining of computations on differentsurface and interface properties of the alloy this correction is applied Structural properties at 001 surface of the alloy and its interface with GaAs 001 substrate were studied Relative stability ofdifferent terminations were investigated and more stable terminations at surface and interface weredetermined The results show that both the standard terminations of the alloy beside Fe rich terminationallocate in the stable region of the phase diagram On the other hand at interface of the alloy withGaAs only CoCo As standard termination is formable while the modified termination FeFe As and theFeGa As complex termination occupy some part of the allowable region of the phase diagram Comparison between cohesive energy of the bulk compounds corresponding to the surface orinterface showed that this quantity could be used as a criteria for relative favor of atoms to be at surfaceor interface terminations The surface or interfacial effects on magnetic and electronic properties werestudied It was seen that due to changes in electronic structures of surface and interface atoms halfmetallic character is not held across surface and interface terminations In the second part we studied a group of 3d transition element arsenides in the met stable phase of zincblende These studies were performed from point of view of the topology of the electronic chargedensity at different volumes hydrostatic pressures At first we introduced the applied method forcalculation of the topology of the charge density as an scalar field then this method was applied forstudying XAs X V Cr Mn Fe Co compounds Topological calculations were performed usingCRITIC or TECD programs that use charge densities prepared by WIEN2k and PWscf codesrespectively After determining topology of critical points of charge density in this zin blende structures we did more detailed investigations on the behavior of topological parameters during volume changesand also varying the atomic number of 3d transition element As a result of these studies we found thatbulk modulus has near correlation with the value of charge at bond critical points so that the morecharge at bond points the less compressibility of the bonds and so the higher bulk modulus On theother hand near correlation between directionality of the bonds and cohesive energy of under studystructures was observed in addition by comparison between topology of the charge in two spin

خسروي زاده، شكوفه

1.مطالعه ابتدا به ساكن سطح ﴿001﴾ Co2FeSi و مرز مشترك ﴿001﴾ Co2FeSi/GaAs و 2. توصيف توپولوژيكي پيوند و مغناطيس در تركيبات﴿XAs(X=V ، Cr ، Mn ،Fe ،Co

اسپين ترونيك , نيم فلزات , ساختارهاي لايه نازك , توپولوژي چگالي بار الكتروني