Inverse-Heusler合金Ti_2NiAl/GaAs隧道异质结的自旋极化和电磁特性
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摘要
基于密度泛函理论的第一性原理计算,研究了Hg_2CoTi型Inverse-Heusler合金Ti_2NiAl和GaAs异质界面上的原子相互作用、磁性、态密度和自旋极化.结果表明,在所研究的12种异质结构(包括顶位和桥位连接)中,界面态的存在不同程度地破坏了合金的半金属性,导致不超过75%的自旋极化率发生;仅当Heusler合金TiAl端面的Al原子或者TiNi端面的Ti原子位于As原子的顶位时,合金异质结可以保留着约72%的自旋极化率,根据Julliere模型,能最大实现68.9%的自旋电子迁移率,有望在隧穿磁阻中实际应用.
For Hg_2CoTi-type Inverse-Heusler alloy Ti_2NiAl/GaAs tunnel heterojunction, the interaction, magnetism, density of states and spin polarization of atoms at the interface were investigated systematically based on the first-principle calculation within the density functional theory(DFT). The calculated results reveal that the interface states destroy the structural half-metallicity in different levels and lead to the spin polarization less than 75%. Among all the 12 hetero-structures combined by top(T) and bridge(B)sites, only when alloy Al atom in TiAl terminal face or Ti atom in TiNi terminal face locates at the top site of As atom, the hetero-junction can still retain around 72% of spin polarization and achieve the maximum spin-electron mobility of 68.9% according to the Julliere model, which are expected for further application in Tunnel Magneto Resistance(TMR).
For Hg_2CoTi-type Inverse-Heusler alloy Ti_2NiAl/GaAs tunnel heterojunction, the interaction, magnetism, density of states and spin polarization of atoms at the interface were investigated systematically based on the first-principle calculation within the density functional theory(DFT). The calculated results reveal that the interface states destroy the structural half-metallicity in different levels and lead to the spin polarization less than 75%. Among all the 12 hetero-structures combined by top(T) and bridge(B)sites, only when alloy Al atom in TiAl terminal face or Ti atom in TiNi terminal face locates at the top site of As atom, the hetero-junction can still retain around 72% of spin polarization and achieve the maximum spin-electron mobility of 68.9% according to the Julliere model, which are expected for further application in Tunnel Magneto Resistance(TMR).
引文
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[2] Zutic I,Fabian J,Das Sarma S.Spintronics:fundamentals and applications [J].Rev.Mod.Phys.,2004,76:323.
[3] KüblerJ,Williams A R,Sommers C B.Formation and coupling of magnetic moments in Heusler alloys [J].Phys.Rev.B,1983,28:1745.
[4] Galanakis I,Dederichs P H,Papanikolaou N.Slater-Pauling behavior and origin of the half-metallicity of the full-Heusler alloys [J].Phys.Rev.B,2002,66:174429.
[5] Hasnip P J,Smith J H,Lazarov V K.Ab initio studies of disorder in the full Heusler alloy Co2FexMn1-xSi [J].J.Appl.Phys.,2013,113:315.
[6] Sakuraba Y,hattori M,Oogane M,et al.Giant tunnel magnetoresistance in Co2MnSi/Al-O/Co2MnSi magnetic tunnel junctions [J].Appl.Phys.Lett.,2006,88:192508.
[7] Tezuka N,Ikeda N,Sugimoto S,et al.175% tunnel magnetoresistance at room temperature and high thermal stability using Co2FeAl0.5Si0.5 full-Heusler alloy electrodes [J].Appl.Phys.Lett.,2006,89:252508.
[8] Marukame T,Ishikawa T,Hakamata S,et al.Highly spin-polarized tunneling in fully epitaxial Co2Cr0.6Fe0.4Al/MgO/Co50Fe50 magnetic tunnel junctions with exchange biasing [J].Appl.Phys.Lett.,2007,90:012508.
[9] Yamamoto M,Ishikawa T,Taira T,et al.Effect of defects in Heusler alloy thin films on spin-dependent tunneling characteristics of Co2MnSi/MgO/Co2MnSi and Co2MnGe/MgO/Co2MnGe magnetic tunnel junctions [J].J.Phys.:Condens.Matter,2010,22:164212.
[10] Ambrose T,Krebs J J,Prinz G A.Magnetic properties of single crystal Co2MnGe Heusler alloy films [J].J.Appl.Phys.,2000,87:5463.
[11] Muri D,School D,Siegmann H C,et al.Observation of the exchange interaction at the surface of a ferromagnet [J].Phys.Rev.Lett.,1988,61:758.
[12] MacDonld A H,Jungwwirth T,Kasner M.Temperature dependence of itinerant electron junction magnetoresistance [J].Phys.Rev.Lett.,1998,81:705.
[13] Shang C H,Nowak J,Jansen R,et al.Temperature dependence of magnetoresistance and surface magnetization in ferromagnetic tunnel junctions [J].Phys.Rev.B,1998,58:r2917.
[14] Hoedequin C,Ristoiu D,Ranno L,et al.On the cross-over from half-metal to normal ferromagnet in NiMnSb [J].Eur.Phys.J.B,2000,16:287.
[15] Supatutkul C,Pramchu S,Jaroenjittichai A P,et al.Density functional theory investigation of surface defects in Sn-doped ZnO[J].Surf.Coat.Tech.,2016,306:364.
[16] Borca C N,Komesu T,Jeong H K,et al.Evidence for temperature dependent moments ordering in ferromagnetic NiMnSb (100) [J].Phys.Rev.B,2001,23:052409.
[17] Atterma J J,De Wijs G A,De Groot R A.Optimizing performance of half-metals at finite temperature [J].J.Phys.:Condens.Mater.,2007,19:315212.
[18] Wu B,Yuan H K,Kuang A L,et al.Tunable magnetism and half-metallicity in bulk and (100) surface of quaternary Co2MnGe1-xGax Heusler alloy [J].J.Phys.D,2011,44:405301.
[19] Wu B,Yuan H K,Kuang A L,et al.Thermodynamic Stability,Magnetism and half-metallicity of Heusler alloy Co2MnX[X=Si,Ge,Sn] (100) surface [J].Appl.Surf.Sci.,2012,258:4945.
[20] Skaftouros S,?zdogan K,Sasioglu E,et al.Generalized Slater-Pauling rule for the inverse Heusler compounds [J].Phys.Rev.B,2013,87:024420.
[21] Liu G D,Dai X F,Liu H Y,et al.Mn2CoZ (Z = Al,Ga,In,Si,Ge,Sn,Sb) compounds:Structural,electronic,and magnetic properties [J].Phys.Rev.B,2008,77:014424.
[22] Kervan N,Kervan S.Half-metallic properties of Ti2FeSi full-Heusler compound [J].J.Phys.Chem.Solids,2011,72:1358.
[23] Kervan S,Kervan N.Spintronic properties of the Ti2CoB Heusler compound by density functional theory [J].Solid.State.Commun.,2011,151:1162.
[24] Lei.F,Tang C,Wang S,et al.Half-metallic full-Heusler compound Ti2NiAl:A first-principles study [J].J.Alloys Compd.,2011,509:5187.
[25] Feng Y,Wu B,Yuan H K,et al.Magnetism and half-metallicity in bulk and (100) surface of Heusler alloy Ti2CoAl with Hg2CuTi-type structure [J].J.Alloys Compd.,2013,557:202.
[26] Song W,Wang B,Wang J L,et al.Structures and electronic properties of Ni–Al alloy clusters from first-principles calculations [J].J.Clust.Sci.,2017,28:2575.
[27] Perdew J P,Burke K,Ernzerhof M,et al.Generalized gradient approximation made simple [J].Phys.Rev.Lett.,1996,77:3865.
[28] Vanderbilt D.Soft self-consistent pseudopotentials in a generalized eigenvalue formalism [J].Phys.Rev.B,1990,41:7892.
[29] Fan Q Y,Wei Q,Chai C C,et al.Structural,anisotropic and thermodynamic properties of boron carbide:First principles calculations[J].Indian J.Pure Appl.Phy.,2016,54:227.
[30] Julliere M.Tunneling between ferromagnetic films [J].Phys.Lett.A,1975,54:225.