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SPINTRONICS AND FERROMAGNETIC SEMICONDUCTORS Tomasz Dietl, Warsaw Discontinuous technologies New information carrier - electron photon, flux (SQUID loops), vortex (type II superconductors); - spin rather than charge, domain walls,... Discontinuous technologies New information carrier - electron photon, flux (SQUID loops), vortex (type II superconductors); - spin rather than charge, domain walls,... New principle of device operation quantum devices, spin transistors,... Discontinuous technologies New information carrier - electron photon, flux (SQUID loops), vortex (type II superconductors); - spin rather than charge, domain walls,... New principle of device operation quantum devices, spin transistors,... New architecture - reprogramable devices, SOC - physical, chemical and biological processes - quantum computing Discontinuous technologies New information carrier - electron photon, flux (SQUID loops), vortex (type II superconductors); - spin rather than charge, domain walls,... New principle of device operation quantum devices, spin transistors,... New architecture - reprogrammable devices, SOC - physical, chemical and biological processes - quantum computing => Spintronics Discontinuous technologies Spintronics -- specific goals reading of magnetic information - magnetisation (field) sensors Spintronics -- specific goals reading of magnetic information - magnetisation (field) sensors TMR Spintronics -- specific goals reading of magnetic information - magnetisation (field) sensors writing of magnetic information - magnetisation manipulation other than magnetic field TMR Spintronics -- specific goals reading of magnetic information - magnetisation (field) sensors writing of magnetic information - magnetisation manipulation other than magnetic field generation of spin polarised currents - ferromagnetic metallic electrodes (spin injection) - spin selective ferromagnetic barriers (spin filtering) spin detectors - spin/charge conversion TMR Spintronics -- specific goals reading of magnetic information - magnetisation (field) sensors writing of magnetic information - magnetisation manipulation other than magnetic field generation of spin polarised currents - ferromagnetic metallic electrodes (spin injection) - spin selective ferromagnetic barriers (spin filtering) spin detectors - spin/charge conversion single spin manipulation - quantum information (low temperatures acceptable) TMR Spintronics -- materials aspects Why do not combine complementary resources of ferromagnets and semiconductors? TopGaN Spintronics -- materials aspects Why do not combine complementary resources of ferromagnets and semiconductors? hybrid semiconductor/ferromagnetic metal structures TopGaN Spintronics -- materials aspects Why do not combine complementary resources of ferromagnets and semiconductors? hybrid semiconductor/ferromagnetic metal structures ferromagnetic semiconductors multifunctional materials TopGaN SPINTRONICS AND FERROMAGNETIC SEMICONDUCTORS Tomasz DIETL Warsaw collaborators: T. Andrearczyk, P. Kossacki, M. Sawicki Warsaw F. Matsukura, H. Ohno Sendai J. Cibert, D. Ferrand, S. Tatarenko Grenoble C.T. Foxon, B.L. Gallagher, K. Edmonds, K.Y. Wang Nottingham T. Jungwirth (Prague) J. Koenig, A.H. MacDonald, J. Sinova Texas reviews: Semicond. Sci. Technol. 17 (2002) ; MRS Bulletin, October 2003, p. 714, Europhys. News 34 (2003) 216. support: FENIKS, AMORE -- EC projects, Polonium Project Ohno Semiconductor Spintronics ERATO Project of JST Humboldt Foundation OUTLINE 1.Frromagnetic semiconductors background 2.Understanding of carrier-controlled ferromagnetic semiconductors 3. Magnetisation manipulation 4. Have we a functional room temperature ferromagnetic semiconductor? magnetic semiconductors short-range ferromagnetic super- or double exchange EuS, ZnCr 2 Se 4, La 1-x Sr x MnO 3,... Ferromagnetic semiconductors magnetic semiconductors short-range ferromagnetic super- or double exchange EuS, ZnCr 2 Se 4, La 1-x Sr x MnO 3,... EuS/KCl,... diluted magnetic semiconductors long-range hole-mediated ferromagnetic exchange IV-VI: p-Pb 1-x-y Mn x Sn y Te Story et al. (Warsaw, MIT) PRL86 III-V: In 1-x- Mn x As Ohno et al. (IBM) PRL92 Ga 1-x- Mn x As Ohno et al. (Tohoku) APL96 T C 100 K for x = 0.05 II-VI: Cd 1-x Mn x Te/Cd 1-x-y Zn x Mg y Te:N QW Haury et al. (Grenoble, Warsaw) PRL97 Zn 1-x Mn x Te:N,P Ferrand et al. (Grenoble, Warsaw) PRB01 Ferromagnetic semiconductors magnetic semiconductors short-range ferromagnetic super- or double exchange EuS, ZnCr 2 Se 4, La 1-x Sr x MnO 3,... EuS/KCl,... diluted magnetic semiconductors long-range hole-mediated ferromagnetic exchange IV-VI: p-Pb 1-x-y Mn x Sn y Te Story et al. (Warsaw, MIT) PRL86 III-V: In 1-x- Mn x As Ohno et al. (IBM) PRL92 Ga 1-x- Mn x As Ohno et al. (Tohoku) APL96 T C 100 K for x = 0.05 II-VI: Cd 1-x Mn x Te/Cd 1-x-y Zn x Mg y Te:N QW Haury et al. (Grenoble, Warsaw) PRL97 Zn 1-x Mn x Te:N,P Ferrand et al. (Grenoble, Warsaw) PRB01 III-V and II-VI DMS: quantum nanostructures and ferromagnetism combine Ferromagnetic semiconductors Zener/RKKY model of carrier-controlled ferromagnetism in DMS Mn state and its coupling to carriers in DMS Mn: 3d 5 4s 2 II-VI: Mn electrically neutral (3d 5, S = 5/2) doping by acceptors necessary III-V, IV: Mn acts as source of spins and holes sp-d exchange interaction => -- large p-d hybridisation and intra-site Hubbard U => Kondo hamiltonian H = - N o Ss => strong Mn hole p-d exchange -- (Cd,Mn)Te: N o eV Gaj et al. (Warsaw, Paris) SSC79 -- (Ga,Mn)As: N o eV Okabayashi et al. (Tokyo) PRB98, Szczytko et al. (Warsaw)PRB01 -- no s-d hybridisation => weaker Mn electron s-d exchange N o 0.2 eV Gaj et al. (Warsaw, Paris) SSC79 giant spin splitting of bands proportional to Mn magnetization Zener/RKKY model of hole-controlled ferromagnetism in DMS Driving force: lowering of the hole energy due to redistribution between hole spin subbands split by p-d exchange interaction T.D. et al.,97- MacDonald et al. (Austin) 99- k EFEF Zener/RKKY model of hole-controlled ferromagnetism in DMS Driving force: lowering of the hole energy due to redistribution between hole spin subbands split by p-d exchange interaction T.D. et al.,97- MacDonald et al. (Austin) 99- k EFEF No adjustable parameters T C ~ 2 (s) DOS Essential ingredient: Complexity of the valence band structure has to be taken into account Mn-based p-type DMS to which p-d Zener model has been found to apply Theory: T. D et al. (Warsaw, Tohoku, Grenoble) Science00, PRB01 Jungwirth et al. (Austin, Prague, PRB02), also UCSD, NRL, Expl.: Tohoku, Kanagawa, Tokyo, Grenoble, PSU, NRL, Notre Dame, UCSB, Nottingham, x Mn = 5% p = 3.5x10 20 cm -3 T C CW T C (p,x) consistent with p-d Zener model Indication of ferromagnetism in n-Zn 1-x Mn x O:Al Temperature (K) (mT) T C 160 mK consistent with s-d Zener model R xx ( ) Magnetic field (T) 50mK 60mK 75mK 100mK 125mK 150mK 200mK Andrearczyk et al. (Warsaw, Yokohama) ICPS00 n = 1.4x10 20 cm -3 x = 0.03 p-d Zener model for p-type DMS the model explains/predicted: -- T C (x, p, n), spin polarization, M(T,H), -- magnetic stiffness (domain width, spin wave spectrum) -- anomalous Hall effect -- magnetoresistance (WLR) and anisotropic magnetoresistance -- a.c. conductivity and magnetic circular dichroism -- T.D. et al.,97- A.H. MacDonald et al. 99- Spintronic functionalities of ferromagnetic DMS Spintronic functionalities of ferro DMS As metal ferromagnets: spin injectors GMR, TMR, AMR, PHE Kerr effect current-induced magnetisation switching Spintronic functionalities of ferro DMS Magnetisation manipulation unique to magnetic semiconductor: electric field light epitaxial strain Electric field Tuning of magnetic ordering by electric field (ferro-FET) (In,Mn)As Ohno et al. (Tohoku, Warsaw) Nature 00 M I VHVH Tuning magnetic ordering by electric field (ferro-FET) (In,Mn)As Ohno et al. (Tohoku, Warsaw) Nature 00 M I VHVH V QW barriers p doped n doped undoped Hole-induced ferromagnetism in a pin diode ferro-LED (Cd,Mn)Te Hole liquidDepleted EvEv EcEc EFEF V Boukari et al. (Grenoble, Warsaw) PRL02 Photoluminescence Light Effect of illumination in (Cd,Mn)Te p-i-n diode V QW illumination EvEv EcEc EFEF Boukari et al. (Grenoble, Warsaw) PRL02 0 V 1.5 K Enhancement of ferromagnetism n+n+ p+p+ Effect of illumination in (Cd,Mn)Te p-i-p diode V QW illumination Boukari et al. (Grenoble, Warsaw) PRL02 Destruction of ferromagnetism p+p+ p+p+ EFEvEFEv EcEc Temperature Hole concentration p = constT = const Epitaxial strain Magnetic anisotropy -- epitaxial strain engineering Tensile strain e.g. (Ga,Mn)As/(In,Ga)As Compressive strain e.g. (Ga,Mn)As/GaAs Epitaxial-strain-induced magnetic anisotropy Sawicki et al.(Warsaw, Wuerzburg)04 after T.D. et al. (Warsaw, Tohoku) PRB 01 Ga 1-x Mn x As/GaAs compressive strain j z = 3/2 x = 0.053 Epitaxial-strain-induced magnetic anisotropy Sawicki et al. (Warsaw, Wuerzburg)04 after T.D. et al. (Warsaw, Tohoku) PRB 01 Ga 1-x Mn x As/GaAs compressive strain j z = 3/2 j z = 1/2 theory x = 0.053 Reorientation transition theory and expt. annealing Sawicki et al. (Warsaw, Wuerzburg)04 after T.D. et al. (Warsaw, Tohoku) PRB 01 Ga 1-x Mn x As/GaAs compressive strain j z = 3/2 j z = 1/2 theory x = 0.053 Controlling locally magnetisation direction to be demonstrated Ferromagnetic quantum dot array M M s /4 Can we push T C higher? Strategies Two strategies for pushing T C higher -- increasing p and/or x in existing ferromagnetic DMS -- searching for DMS with greater coupling constant 2 (E F ) T.D. et al. (Warsaw, Tohoku, Grenoble) Science00 Strategies Two strategies for pushing T C higher -- increasing p and/or x in existing ferromagnetic DMS -- searching for DMS with greater coupling constant 2 (E F ) Obstacles -- self-compensation -- solubility limits -- tight binding of holes by TM ions (Zhang-Rice polaron) T.D. et al. (Warsaw, Tohoku, Grenoble) Science00 1/ Where are we? Wang/ Sawicki (Nottingham, Warsaw) remanent magnetisation and 1/ vs. T hysteresis loops M REM T C = 173 K T C CW Record Curie temperature (K) T C in (III,Mn)As The progress due to increase of p by low temperature annealing out diffusion of Mn I : Wojtowicz et al. (Notre Dame, Warsaw, Berkeley) PRB02; APL04 Edmonds et al. (Nottingham, Warsaw) PRL04 IBM, Tohoku, Tokyo, Notre Dame, PSU, Tohoku, Nottingham, (Ga,Mn)As growth phase diagram phase separation GaAs + MnAs LT Ga 1-x Mn x As:Mn I roughening polycrystal after Matsukura and Ohno SUMMARY Mn-based arsenides, also antymonides, tellurides -- basic thermodynamic, magnetoelastic, optical, and also optical properties understood (p-d Zener model) SUMMARY Mn-based arsenides, also antymonides, tellurides -- basic thermodynamic, magnetoelastic, optical, and also optical properties understood (p-d Zener model) -- magnetisation manipulations by electric field, light, and epitaxial strain demonstrated SUMMARY Mn-based arsenides, also antymonides, tellurides -- basic thermodynamic, magnetoelastic, optical, and also optical properties understood (p-d Zener model) -- magnetisation manipulations by electric field, light, and epitaxial strain demonstrated -- role of point defects (interstitials) and also extended defects (e.g., MnAs precipitates) elucidated OTHER SYSTEMS Zener model prediction of T C for semiconductors containing 5% Mn d 5, p = 3.5 cm -3 T. D. et al. (Warsaw, Tohoku, Grenoble) Science00, PRB01 Light elements: strong p-d hybridisation weak spin-orbit interaction Materials showing hysteresis and spontaneous magnetization at 300 K wz-c- (Ga,Mn)N, (In,Mn)N, (Ga,Cr)N, (Al,Cr)N, (Ga,Gd)N, (Ga,Mn)As, (In,Mn)As, (Ga,Mn)Sb, (Ga,Mn)P:C (Zn,Mn)O, (Zn,Ni)O, (Zn,Co)O, (Zn,V)O, (Zn,Fe,Cu)O (Zn,Cr)Te (Ti,Co)O 2, (Sn,Co)O 2, (Sn,Fe)O 2, (Hf,Co)O 2 (Cd,Ge,Mn)P 2, (Zn,Ge,Mn)P 2, (Zn,Sn,Mn)As 2 (Ge,Mn) (La,Ca)B 6, C 60, C, Materials showing hysteresis and spontaneous magnetization at 300 K wz-c- (Ga,Mn)N, (In,Mn)N, (Ga,Cr)N, (Al,Cr)N, (Ga,Gd)N, (Ga,Mn)As, (In,Mn)As, (Ga,Mn)Sb, (Ga,Mn)P:C (Zn,Mn)O, (Zn,Ni)O, (Zn,Co)O, (Zn,V)O, (Zn,Fe,Cu)O (Zn,Cr)Te (Ti,Co)O 2, (Sn,Co)O 2, (Sn,Fe)O 2, (Hf,Co)O 2 (Cd,Ge,Mn)P 2, (Zn,Ge,Mn)P 2, (Zn,Sn,Mn)As 2 (Ge,Mn) (La,Ca)B 6, C 60, C, In many cases high T C consistent with ab initio computations within DFT Materials showing hysteresis and spontaneous magnetization at 300 K wz-c- (Ga,Mn)N, (In,Mn)N, (Ga,Cr)N, (Al,Cr)N, (Ga,Gd)N, (Ga,Mn)As, (In,Mn)As, (Ga,Mn)Sb, (Ga,Mn)P:C (Zn,Mn)O, (Zn,Ni)O, (Zn,Co)O, (Zn,V)O, (Zn,Fe,Cu)O (Zn,Cr)Te (Ti,Co)O 2, (Sn,Co)O 2, (Sn,Fe)O 2, (Hf,Co)O 2 (Cd,Ge,Mn)P 2, (Zn,Ge,Mn)P 2, (Zn,Sn,Mn)As 2 (Ge,Mn) (La,Ca)B 6, C 60, C, In many cases high T C consistent with ab initio computations within DFT None proven to be 300 K ferromagnetic semiconductor Phase diagrams unknown Each system brings new challenges CONCLUSIONS ( Ga,Mn)As, p-(Cd,Mn)Te, emerges as the best understood ferromagnet Beginning of the road for magnetically doped nitrides and oxides END Energy levels of transition metal impurities in II-VI compounds and III-V compounds d n /d n+1 d n /d n-1 d n /d n+1 Mn neutral Mn acceptor Zunger, Baranowski, Vogel, Langer, Fujimori,...


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