First-principles Study Of Electronic, Magnetic And Optical Properties Of Yttrium-based Heusler Alloy

In the last decades,spintronic devices have attracted much attention in view of their great applications,but one difficult problem with this is efficient spin injection.Up to now,Heusler alloys are most suitable for spintronic devices due to their similar crystal structure with conventional semiconductors,high spin polarization and high Curie temperature.Especially,half-metallic(HM)magnetic Heusler alloys are the most effective to enhance the efficiency of spin electron injection because they behave like metal for one spin channel and like semiconductor for the other spin channel,leading to a full 100%spin polarization at the Fermi level(EF).Therefore,more and more Heusler alloys with various structures have been predicted theoretically and may be helpful in either experimental fabrication or future practical application.Inspired by the above statements,in this paper by using the first-principles calculations based on the density functional theory(DFT),we investigate several yttrium-based Heusler alloys,the conclusions are given as follows:(1)The structural,electronic and magnetic properties of yttrium-based full-Heusler alloys Y2CrZ(Z=Al,Ga,In)in Hg2CuTi structure have been investigated.For three alloys,the ferromagnetic states are the most favorable states among the possible magnetic configurations.The Y2CrZ(Z=Al,Ga,In)alloys are HM ferromagnets with spin-up band gaps at equilibrium lattice constants,respectively.The origins of the spin-up band gaps are mainly attributed to the d-d hybridization.Besides,the HM characters are kept in larger lattice constant range for Y2CrZ(Z=Al,Ga,In)alloys.The formation energies and the cohesion energies indicate the stability of these three alloys.The much higher Curie temperatures than room temperature show these alloys are suitable for spintronics applications.In addition,the total magnetic moments of 3?B/f.u.for these alloys satisfy the Slater-Pauling rule Mt=18-Zt.(2)The structural,electronic,elastic,magnetic and optical properties of the yttrium-based full-Heusler alloys Y2CrZ(Z=Si,Ge,Sn)have been studied.It is found that for all three alloys the Hg2CuTi+FiM state is the most stable state.The Y2CrZ(Z=Si,Ge,Sn)alloys are HM ferrimagnets with indirect spin-up band gap and their HM characters are maintained in large lattice constant range.Both the negative formation energies and the large cohesion energies indicate these three alloys are thermodynamically stable and may be fabricated experimentally.The total magnetic moments of these three alloys are 2 ?B/f.u.,satisfying the Slater-Pauling rule Mt =18-Zt.The elastic and optical properties of Y2CrZ(Z=Si,Ge,Sn)have been also studied to explore the potential value in practical application.(3)The structural,electronic,magnetic and optical properties of yttrium-based Heusler alloys Y3Si,Y2CrSi and ScYCrSi have been investigate and compared.The calculated results show that Y3Si,Y2CrSi and ScYCrSi alloys are stable in D03-FM,Hg2CuTi-FM and YI-FM configurations,respectively.The Y3Si alloy is a conventional metal,while Y2CrSi and ScYCrSi alloys are HM with spin-up band gap.The HM nature of Y2CrSi and ScYCrSi is robust in larger lattice constant range.The total magnetic moments Mt of Y3Si,Y2CrSi and ScYCrSi alloys are 0.943,2,2 ?B/f u.,respectively,the latter two satisfy the Slater-Pauling rule t=18-Zt.Finally,the optical properties of three alloys are studied to explore the appropriate condition for optoelectronic application field.