Dilute moment ferromagnetic semicinductors for spintronics

1. Cambridge Dilute moment ferromagnetic semicinductors for spintronics Tomas Jungwirth Bryan Gallagher, Tom Foxon, Richard Campion, Kevin Edmonds, Andrew Rushforth, Devin Giddings, Chris King, et al. Jan Mašek, Alexander Shick Karel Výborný, Jan Zemen, Vít Novák, et al. Prague Nottingham NANOSPIN Jorg Wunderlich, David Williams, Andrew Irvine, Kaiyou Wang, Elisa De Ranieri, et al. CNRS, Wuezburg, Warsaw, Thales Texas Universities Jairo Sinova, Allan H. MacDonald. et al.

2. Ga py Mn As Mn p px s V Hso (Ga,Mn)As (and realated DMSs) & spintronics: Ideal systems for exploring basic physics and new functionality concepts Dilute moment ferromagnets based on semiconductor material: dependence on doping low saturation magnetization Ferromagnetic Mn-Mn coupling mediated by GaAs host-like As p-orbital band states: strongly exchange split and SO coupled yet relatively simple carrier bands

3. majority _ _ _ FSO _ FSO I minority e.g. anomalous Hall effect V Spintronics based on extraordinary magnetoresistance effects (AHE, AMR, STT,TMR,....) Extraordinary magnetoresistance: response to internal magnetization in ferromagnets often via quantum-relativistic spin-orbit coupling anisotropic magnetoresistance For decades controversial in conventional metal FMs: model of (non-SO-coupled non-exchange-split) s-state carriers and localized d-states  difficult to match with microscopic bands of mixed s-d character

4. M M current   ) ) [110] ky kx Origin of AMR Basic symmetry arguments for zincblende DMSs (GaMnAs) SO-coupling – spherical model FM exchange spiitting scattering rate ~(k . s)2 ~Mx . sx hot spots for scattering of states moving  M  R(M  I)> R(M || I) Successful microscopic modelling AMRtheor. AMRexp. still R(M  I)> R(M || I) plus magnetocrystalline anisotropy corrections (M vs. crystal axes)

5. A family of new AMR effects dicovered in GaMnAs - TAMR sensor/memory elemets TAMR TMR no need for exchange biasing or spin coherent tunneling Au predicted and recently confirmed to exist in conventional metal FMs • - CBAMR spintronic transistor • combining processing with • permanent storage and p-type • and n-type transistor characteristics predicted to exists in conventional metal FMs

6. Spintronic transistor based on CBAMR Huge, gatable, and hysteretic MR Single-electron transistor Two "gates": electric and magnetic

7. Q VD Source Drain Gate VG Spintronic transistor based on CBAMR magnetic electric & control of Coulomb blockade oscillations  magnitude of MR reaches magnitude of CB oscillations

8. M || <111> M || <100> Strong spin-orbit coupling  band structure depends on M  chemical potential depends on M • CBAMR if change of |(M)| ~ e2/2C • In (Ga,Mn)As ~ meV (~ 10 Kelvin) • In room-T ferromagnet change • of |(M)|~100K

9. CBAMR SET • Generic effect in FMs with SO-coupling • ~10 K in GaMnAs, ~100 K in room-Tc metal FM • Combines electrical transistor action • with magnetic storage • Switching between p-type and n-type transistor • by M  programmable logic

10. Ga py Mn As Mn p px s V Hso (Ga,Mn)As (and realated DMSs) & spintronics: Ideal systems for exploring basic physics and new functionality concepts Dilute moment ferromagnets based on semiconductor material: dependence on doping low saturation magnetization Ferromagnetic Mn-Mn coupling mediated by GaAs host-like As p-orbital band states: strongly exchange split and SO coupled yet relatively simple carrier bands unprecedented micromagnetics  Jorg Wunderlich's talk