First Principles Study Of Electronic Stucture And Magneticnproperties Of Heusler Alloy Heterojunctions

Heusler alloy is a kind of intermetallics with rich physical properties,such as magnetoresistance effects,large magnetic-field-induced strain effect,half-metallic property and superconductivity of containing rare earth elements,etc.Theoretically,the Heusler-type half metallic material with 100%spin polarization can be used as the electrode material of magnetic tunnel,thereby improving the value of magnetoresistance,and has important application prospects in spin injection,spin-valve and magnetic random access memory.In recent years,with the rapid development of industry and the more and more prominent energy problem,more and more researches have been focused on the thermoelectric materials,and how to use energy effectively and recycle waste heat is particularly important.The thermoelectric materials not only can realize the transformation between the heat energy and electric energy,but also have the advantages of small volume,light weight and no noise in work.Therefore,more new thermoelectric materials with good performance have been explored in this work,hoping that they can be applied to the recycling of waste heat,refrigeration and other fields.Half-heusler alloy has good characteristics such as non-toxic,mechanical stability and thermal stability,etc.It is a kind of important middle temperature thermoelectric material.The structure of full-Heusler alloy is similar to that of half-heusler alloy and also has good thermoelectric properties.The precondition of being a thermoelectric material is that its electronic structure needs to have band gap,with semiconducting character,and the transport properties of carriers can be regulated by doping.In this paper,using the first principle method based on the density functional theory and Boltzmann transport equation,calculating the Heusler alloys Ti₂Cr_1-x/4Mo_x/4Z?Z=Ge,Sn??x=1,2,3,4?by substituting the Cr atoms with Mo atoms and study the structural,electronic and magnetic properties as well as the thermoelectric transport properties.The electronic structure and magnetic properties of Heusler alloy Ti₂CrSn,the electronic structure of Heusler alloy Ti₂FeGa?001?,?110?,?111?surface and the electron structure and magnetic properties of Ti₂NiIn/Ti₂CrSn?001?interface are studied.The main conclusions are as follows:Ti₂Cr_1-x/4Mo_x/4Ge?x=1,2?and Ti₂Cr_1-x/4Mo_x/4Sn?x=1,2,3?have the fully compensated ferrimagnetic semiconducting nature with totally zero magnetism.The two full substitution alloys Ti₂MoGe and Ti₂MoSn belong to nonmagnetic semiconductors and the total moment M_t of all the predicted semiconductors satisfy the rule of M_t=Z_t-18 per unit cell since their valence electron numbers Z_t are all 18.Moreover,the three predicted semiconductors Ti₂Cr_1/2Mo_1/2Ge,Ti₂MoGe and Ti₂MoSn have high thermoelectric power factor,indicating that they are the candidate thermoelectric materials for moderate temperature application.The inverse Heusler compound Ti₂CrSn with L2₁ phase is predicted to be antiferromagnetic semiconductor with an indirect gap of 0.2 eV.The semiconducting character is stable within a large strain from-6%to 6%.The Cr,Ti₁ and Ti₂ moments all show a linear change behavior within the strain range of-6%-6%.However,the total zero moment is robust within that strain range.The calculated electronic structure of Ti₂FeGa?001?,?110?and?111?surface show that although it does not have 100%spin polarization,it still maintains a high spin polarization.Therefore,it can be applied to magnetic tunnel junction based on Heusler alloys as the ferromagnetic layers.Heusler alloy Ti₂NiIn belongs to half-metal with high Curie temperature and lattice constant is 6.42?.Heusler alloy Ti₂CrSn is semiconductor and the lattice constant is 6.48?,which has been predicted by our calculation recently.The difference of lattice constants between the two alloys is very small and they have small mismatch if as a heterojunction.Calculating on the structural and electronic structure of Ti₂NiIn/Ti₂CrSn?001?interface,and the results show that the structure of In-Sn terminated interface is the most stable structure,and moreover it has retained the half-metallcity,indicating its potential application to devices of magnetic tunnel junction.