1 / 16

Magnetoresistance of tunnel junctions based on the ferromagnetic semiconductor GaMnAs

UNITE MIXTE DE PHYSIQUE associée à l’UNIVERSITE PARIS SUD. Magnetoresistance of tunnel junctions based on the ferromagnetic semiconductor GaMnAs. R. Mattana, J.-M. George, H. Jaffrès, F. NGuyen Van Dau, A. Fert UMP CNRS-THALES, Orsay, France B. Lépine, A. Guivarc’h, G. Jézéquel

javier
Télécharger la présentation

Magnetoresistance of tunnel junctions based on the ferromagnetic semiconductor GaMnAs

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. UNITE MIXTE DE PHYSIQUE associée à l’UNIVERSITE PARIS SUD Magnetoresistance of tunnel junctions based on the ferromagnetic semiconductor GaMnAs R. Mattana, J.-M. George, H. Jaffrès, F. NGuyen Van Dau, A. Fert UMP CNRS-THALES, Orsay, France B. Lépine, A. Guivarc’h, G. Jézéquel UMR CNRS-Université Rennes I, France A. Hamzic, M. Basletic, E. Tafra Department of Physics, Faculty of Science, Zagreb, Croatia

  2. Spin electronics Use the spin of the carriers : • Metallic system (GMR, TMR,..) • Extension to semiconductors • “Source” of spin polarized carriers : Ferromagnetic transition metal • Conductivity mismatch • Chemical reactivity Ferromagnetic semiconductors

  3. GaMnN, ZnCoO: Tc > RT but material optimization still required Ferromagnetic semiconductors Tc : Computed values Dietl et al., Science 287, 1019 (2000) GaMnAs, InMnAs Best knowledge of growth conditions, magnetic & transport properties Heterostructures based on GaMnAs Spin electronics properties

  4. Outline • Magnetic and transport properties of thin films • Structures and growth conditions of MTJs • TMR in single and double barrier MTJs  Spin accumulation • Bias dependence of TMR • Conclusion

  5. Ga1-xMnxAs thin films • x > 7.5% : • Formation of MnAs clusters • x < 4% : • FMbutinsulating • 4% < x <7% : • FMandmetallic can be used as FM electrodes in MTJs

  6. Single barrier Ga1-xMnxAs (x=5.7%) (300Å) GaMnAs GaMnAs GaAs (10Å)  ~ 0.5eV AlAs (17Å) GaAs (10Å) Ga1-xMnxAs (x=4.5%) (3000Å) AlAs 17Å Double barrier GaAs GaMnAs GaMnAs Ga1-xMnxAs (x=5.7%) (300Å) GaAs (10Å) AlAs (17Å) GaAs (50Å) AlAs 17Å AlAs 17Å AlAs (17Å) • Spin transmission across GaAs ? • Spin detection by GaMnAs ? GaAs (10Å) Ga1-xMnxAs (x=4.5%) (3000Å) Valence band profile (holes) • Spin dependent tunneling from GaMnAs • Detection by GaMnAs  observed by Tanaka • Phys. Rev. Lett. 87, 026602 (2001)

  7. GaAs buffer layer at high temperature on semi-insulating GaAs (001) substrates : Ts=580°C; As4/Ga  25 0.3 m/h; As 2x4 surface • Growth of Ga1-xMnxAs & AlAs at low temperature on As rich GaAs surface (As C4x4) : • Ts=230°C; As4/Ga  10 • 0.3 m/h; 1x2 surface GaMnAs AlAs GaMnAs Growth conditions Molecular beam epitaxy (MBE) in a RIBER 2300 system (As4 solid source) : Single barrier MTJ HRTEM P. Galtier

  8. Fabrication process of the tunnel junctions • Four steps of optical lithography • Diameter : 10, 20, 50, 100, 200, 300 µm

  9. GaMnAs/AlAs (17Å)/GaMnAs @ 4K, V=1mV Magnetic field parallel to the [110] axis RS ~ 0.1.cm2 Magnetoresistance of single barrier MTJ • Mr/Ms ~ 30% • TMR (low field)~ 38%

  10. GaMnAs/AlAs/GaMnAs Magnetoresistance of single barrier MTJ R(electrode) ~ 1 k; R(junction) ~ 100 k  R(tunnel) >> R(electrode) TMR (high field) : TMR ~ 675%(progressive saturation of the magnetization)  Large “spin polarization”

  11. Ballistic transmission through the entire I/N/I barrier  is expected to increase considerably the junction resistance. In our case : R(single) ~ R(double) • Sequential tunneling with energy relaxation •  TMR is due to spin accumulation Magnetoresistance of double barrier MTJ GaMnAs/AlAs/GaAs/AlAs/GaMnAs @ 4K, V=1mV Magnetic field parallel to the [110] axis TMR in F/I/N/I/F is expected in following case :

  12. TMR(single) ~ TMR(double) AlAs AP AlAs m , µ ­ ¯ m ­ GaMnAs m , µ eVbP m ­ ¯ ~ 1016 cm-3 ¯ GaMnAs GaAs Evidence of spin splitting in SC Spin accumulation TMR - F/I/N/I/F structure TMR  spin accumulation number of spin flips much smaller than injected spin current Possible for N = SC (small n << 1016 cm-3) Impossible for N=metal (large n~ 1023 cm-3) A. Fert, H. Jaffrès, Phys. Rev. B, 64, 184420 (2001)

  13. Magnon excitation • Tc=60K • Electronic band structure • Exchange coupling smaller • (J ~ 0.1eV) • Barrier shape • Barrier height : ~ 0.5eV •  weak characteristic energies V1/2 ~ 15mV Tunnel properties : Bias dependence Faster decrease compared to metallic junctions : three potential origins :

  14. Without spin accumulation (metallic case) : • V1/2 (double) ~ 2* V1/2(single) • Montaigne et al. APL 73, 2829 (1998) • With a spin accumulation : • Same bias dependence for single and double barrier • V1/2 (double) ~ V1/2(single) AlAs Antiparallel AlAs TMR comes from the spin splitting of the potential (µ and µ) in GaAs  The total voltage drop Vb can be concentrated on one of the junction. ,µ  GaMnAs ,µ ~eVb µ GaMnAs GaAs V1/2 ~ 15mV Tunnel properties : Bias dependence

  15. Spin dependent tunneling of epitaxial tunnel junctions based on the ferromagnetic semiconductor GaMnAs •  Large effect of tunnel magnetoresistance ~ 675% Conclusion Theoretical works on TMR in systems with spin-orbit coupled states

  16. Conclusion • New effect due to semiconductor characteristic (low density of states) - TMR in double MTJ with aSCnonmagnetic central layer  non-relaxed spin splitting of the chemical potential Spin accumulation • - Same bias dependence in single and double barrier MTJs • Spin accumulation in double barrier MTJ : • Spin relaxation in SC layers • Diffusion mechanisms in SC layers

More Related