Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Thin epitaxial ferromagnetic metal...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Outlook
1 Motivations and introduc...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Motivation
Orientation of the magn...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Motivation
Orientation of the magn...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Motivation
Orientation of the magn...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Motivation
Orientation of the magn...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Motivation
Orientation of the magn...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Sample fabrication
Sample characte...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Sample fabrication
Sample characte...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Sample fabrication
Sample characte...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Sample fabrication
Sample characte...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Sample fabrication
Sample characte...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Thickness dependence of anisotropy...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Thickness dependence of anisotropy...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Thickness dependence of anisotropy...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Thickness dependence of anisotropy...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Thickness dependence of anisotropy...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Thickness dependence of anisotropy...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Thickness dependence of anisotropy...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Thickness dependence of anisotropy...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Thickness dependence of anisotropy...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Thickness dependence of anisotropy...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
In-plane expectations from MEL
Est...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
In-plane expectations from MEL
Est...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
In-plane expectations from MEL
Est...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
In-plane expectations from MEL
Est...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
In-plane expectations from MEL
Est...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
In-plane expectations from MEL
Est...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Conclusion
Results
We observed a h...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Acknowledgments
Thanks to all the ...
Introduction
Experimental setup
Results
Magnetoelastic model
Conclusion
Acknowledgments
Thanks for your attention
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Thin epitaxial ferromagnetic metal films on GaAs(001) for spin injection and tunneling magnetoresistive junctions.

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A work done at IBM on thin epitaxial ferromagnetic metal films on GaAs(001) for spin injection and tunneling magnetoresistive junctions showing enhanced magnetic anisotropy by annealing.

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Thin epitaxial ferromagnetic metal films on GaAs(001) for spin injection and tunneling magnetoresistive junctions.

  1. 1. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Thin epitaxial ferromagnetic metal films on GaAs(001) for spin injection and tunneling magnetoresistive junctions. Enhancement of the uniaxial magnetic anisotropy Fran¸cois Bianco IBM - ETH Zurich 1st November 2008 Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  2. 2. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Outlook 1 Motivations and introduction 2 Experimental setup 3 Effect of post-growth annealing 4 Estimate of the magnetoelastic contribution Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  3. 3. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Motivation Orientation of the magnetization Uniaxial magnetic anisotropy Total magnetic energy density Hysteresis curves Motivation Scientific motivations The origin of the uniaxial magnetic anisotropy (UMA) of Fe and FeCo thin films on GaAs(001) is, since its discovery by Krebs et al. in 1987 (J. Appl. Phys. 61, 2596, 1987), still controversial. Get a better understanding the origin of the UMA ... ... by studying the effect of post-growth annealing on the magnetic properties of thin films. Long-term goal/application Spin-injection from Fe31Co69 into GaAs Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  4. 4. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Motivation Orientation of the magnetization Uniaxial magnetic anisotropy Total magnetic energy density Hysteresis curves Orientation of the magnetization The preferred orientation of the magnetization is driven by shape anisotropy (Gauss law) : for thin films favor in-plane magnetization magnetocrystalline anisotropy (Crystal symmetry) magnetoelastic effect (Lattice strain) uniaxial magnetic anisotropy (Interface) Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  5. 5. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Motivation Orientation of the magnetization Uniaxial magnetic anisotropy Total magnetic energy density Hysteresis curves Uniaxial magnetic anisotropy The possible explanations are Krebs J. Appl. Phys. 61, 2596, 1987 Anisotropic bonding The substrate atoms forms rows a the surface, then the symmetry of the atomic orbitals favor bonds in a specific direction. Anisotropic strain Induced by a slight difference in the lattice constant along two directions. Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  6. 6. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Motivation Orientation of the magnetization Uniaxial magnetic anisotropy Total magnetic energy density Hysteresis curves Total magnetic energy density The magnetization goes in the direction of the energy minimum. Utot(ϕ, θ) = −|Hext|Ms cos(ϕ − δ) sin θ UZeeman + Ku sin2 (ϕ − ) sin2 θ Uuniaxial, + 1 2 µ0MsMeff cos2 θ Ushape +Uuniaxial,⊥ + K1( 1 4 sin2 θ sin2 (2ϕ) + cos2 θ) sin2 θ UCubic Depends on three parameters Ku uniaxial magnetic anisotropy constant K1 cubic magnetic anisotropy constant Meff containing the perpendicular uniaxial anisotropy Ku⊥ Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  7. 7. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Motivation Orientation of the magnetization Uniaxial magnetic anisotropy Total magnetic energy density Hysteresis curves Hysteresis curves Ku and K1 are proportional to the slope and the width of the linear part along the HA. Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  8. 8. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Sample fabrication Sample characterization Magneto-optical Kerr effect magnetometer Sample fabrication The samples were fabricated under UHV by MBE on GaAs(001) cooled to -10‰. The Fe31Co69 thin films were protected with an Al capping layer (2–3 nm). Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  9. 9. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Sample fabrication Sample characterization Magneto-optical Kerr effect magnetometer E-Beam deposition The secondary current between the filament and the slug heat it up. Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  10. 10. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Sample fabrication Sample characterization Magneto-optical Kerr effect magnetometer Samples characterization Ku and K1 determined from hysteresis curve measured with magnetooptical Kerr effect magnetometer. Ku,⊥ measured with ferromagnetic resonance (all-optical setup). The in-plane film strain measured with grazing incidence X-ray diffraction. The samples were annealed in an Ar-filled glovebox for 10 min. at each temperatures. Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  11. 11. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Sample fabrication Sample characterization Magneto-optical Kerr effect magnetometer Magneto-optical Kerr effect magnetometer Kerr effect Magnetized material is birefrigent The refractive indexes depends on the magnetization direction The rotation of the light polarization is therfore directly related to the magnetization. Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  12. 12. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Sample fabrication Sample characterization Magneto-optical Kerr effect magnetometer Experimental setup Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  13. 13. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Thickness dependence of anisotropy Effect of the post-growth annealing Perpendicular anisotropy Interpretation Cubic magnetic anisotropy Coercive field Interpretation Thickness dependence of anisotropies (As-grown anisotropies) Interface contribution K = Kvol + Kint t Kvol 1 in excellent agreement with bulk value of Fe31Co69 Assumption : Ku arises only from interface Kvol u = 0 Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  14. 14. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Thickness dependence of anisotropy Effect of the post-growth annealing Perpendicular anisotropy Interpretation Cubic magnetic anisotropy Coercive field Interpretation Huge enhancement of UMA Post-growth annealing temperature Ta induces a huge increase of the UMA Ku follows a linear dependence up to Ta ≈ 300‰ opposite behaviour observed on Fe thin films Shaw et al. J. Appl. Phys., 2007 (Sample thickness 1.9 nm) Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  15. 15. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Thickness dependence of anisotropy Effect of the post-growth annealing Perpendicular anisotropy Interpretation Cubic magnetic anisotropy Coercive field Interpretation Thickness dependence of the enhancement The effect is strongly dependent on the thickness t, and starts at a threshold temperature Tth of about 75‰. Ku = KTth u + κ t ∆T ∆T := Ta − Tth ∆Ku ∆T = κ1 t Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  16. 16. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Thickness dependence of anisotropy Effect of the post-growth annealing Perpendicular anisotropy Interpretation Cubic magnetic anisotropy Coercive field Interpretation As-grown anisotropies vs. anisotropies at 200‰ Effect on the film Kvol 1 and Kint 1 are not changed Kint u is 3 times bigger than the as-grown value Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  17. 17. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Thickness dependence of anisotropy Effect of the post-growth annealing Perpendicular anisotropy Interpretation Cubic magnetic anisotropy Coercive field Interpretation Perpendicular anisotropy (Sample thickness 7.2 nm) Increase like the in-plane anisotropy with a 2-3 times steeper slope Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  18. 18. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Thickness dependence of anisotropy Effect of the post-growth annealing Perpendicular anisotropy Interpretation Cubic magnetic anisotropy Coercive field Interpretation Interpretation 1/2 In- and out-of-plane uniaxial anisotropy Linear increase with post-growth annealing temperature In-plane effect starts at Tth ≈ 75‰ Model for the in-plane increase with Ta Ku = Kint u (∆T) t = Kint u (Tth)+κ∆T t = KTth u + κ t ∆T ∆T := Ta − Tth Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  19. 19. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Thickness dependence of anisotropy Effect of the post-growth annealing Perpendicular anisotropy Interpretation Cubic magnetic anisotropy Coercive field Interpretation Interpretation 2/2 Post-growth annealing Affects mainly the interface Probably creates a coherent interface Zega et al. showed for Fe/GaAs(001) that annealing at 200‰produces a monolayer of alternating Fe and As atoms. Zega, Phys. Rev. Lett. 96(196101) 2006 Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  20. 20. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Thickness dependence of anisotropy Effect of the post-growth annealing Perpendicular anisotropy Interpretation Cubic magnetic anisotropy Coercive field Interpretation Cubic magnetic anisotropy No noticeable trend up to Ta ≈ 250‰ Decreases for Ta > 250‰ Ga atoms begin to diffuse from substrate into Fe for Ta > 220‰ Sano and Miyagawa Jpn. J. Appl. Phys., 30(7) :1434–1441, 1991 Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  21. 21. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Thickness dependence of anisotropy Effect of the post-growth annealing Perpendicular anisotropy Interpretation Cubic magnetic anisotropy Coercive field Interpretation Coercive field No noticeable trend up to Ta = 300‰ Huge jump for Ta > 300‰ Above 300‰changes in crystal structure because of Ga diffusion Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  22. 22. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Thickness dependence of anisotropy Effect of the post-growth annealing Perpendicular anisotropy Interpretation Cubic magnetic anisotropy Coercive field Interpretation Interpretation Cubic anisotropy K1 & Coercive field Not much affected below Ta < 250–300‰ For Ta > 300‰changes are correlated to diffusion of GaAs components Post-growth annealing If Ga atoms replace Fe or Co atoms in the film ⇒ reduction of the crystal symmetry and therefore of K1 Induces probably a change in the crystalline structure of the film Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  23. 23. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments In-plane expectations from MEL Estimate of the in-plane MEL effect Out-of-plane expectations from MEL effect Estimate of the out-of-plane MEL effect Discussion of the estimate Magnetoelastic model Magnetoelastic model (MEL) We will show with GID measurements that MEL effect cannot explain our results. X-ray grazing incidence diffraction (GID) To determine the in-plane lattice strain Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  24. 24. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments In-plane expectations from MEL Estimate of the in-plane MEL effect Out-of-plane expectations from MEL effect Estimate of the out-of-plane MEL effect Discussion of the estimate In-plane expectations from MEL In-plane uniaxial magnetic anisotropy Umel, = B2(e[110] − e[110]) =KuAssumption sin(2ϕ) = B2 sin(2ϕ)e12 If Ku changes with Ta we should find a change of the shear strain e12 ∆Ku = B2∆e12 Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  25. 25. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments In-plane expectations from MEL Estimate of the in-plane MEL effect Out-of-plane expectations from MEL effect Estimate of the out-of-plane MEL effect Discussion of the estimate Estimate of the in-plane MEL effect There is no clear trend within ±0.8‡. Model ∆Ku = B2∆e12 Assuming a change of strain of 0.8 ‡we found a B2 constant several times bigger than Fe thin films Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  26. 26. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments In-plane expectations from MEL Estimate of the in-plane MEL effect Out-of-plane expectations from MEL effect Estimate of the out-of-plane MEL effect Discussion of the estimate Out-of-plane expectations from MEL effect Out-of-plane uniaxial magnetic anisotropy Umel,⊥ = B1(e⊥ − e0) =K⊥Assumption cos2 (θ) If Ku,⊥ changes with Ta we should find a change of the average in-plane strain e0 ∆Ku,⊥ ∝ B1∆e0 Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  27. 27. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments In-plane expectations from MEL Estimate of the in-plane MEL effect Out-of-plane expectations from MEL effect Estimate of the out-of-plane MEL effect Discussion of the estimate Estimate of the out-of-plane MEL effect B1, estimated from as-grown values of K⊥ and e0 assuming only MEL effect, is 44 times larger than B1 for Fe films. Contradictions MEL effect requires more compressive strain But we observe no noticeable trend or only a slight decrease with Ta Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  28. 28. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments In-plane expectations from MEL Estimate of the in-plane MEL effect Out-of-plane expectations from MEL effect Estimate of the out-of-plane MEL effect Discussion of the estimate Discussion of the estimate Points against MEL Strain measured changes in the wrong direction for MEL The estimated B1 is one order of magnitude bigger than Fe thin film B2 is as well several times bigger than Fe thin films value MEL vs. interface bonding The results favor an interpretation of the change of Ku and Ku,⊥ in terms of a magnetocrystalline anisotropy due to modifications of the bonding at the Fe31Co69/GaAs(001) interface. Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  29. 29. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Conclusion Results We observed a huge enhancement of the in- and out-of-plane UMA with Ta. This is related to changes at the FM-SC interface The changes of K1 and of the coercive field indicates to the diffusion of Ga into the film. The MEL cannot explain the effect of Ta Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  30. 30. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Acknowledgments Thanks to all the members of the Physics of Nanoscale System group at IBM, especially Gian Salis Andreas Bischof Marilyne Sousa (Adv. Func. Mat.) S. F¨alt, A. Badolato, and. S. Sch¨on (FIRST lab., ETHZ) Antoine Vanhaverbeke Martin Witzig Axelle Tapponnier (Adv. Func. Mat.) Patrick Bouchon (E. Polytech. Palaisau) Santos F. Alvarado And I am very grateful to Prof. D. Pescia, ETH Zurich Rolf Allenspach, IBM Research Lab. Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin
  31. 31. Introduction Experimental setup Results Magnetoelastic model Conclusion Acknowledgments Thanks for your attention “Science has explained nothing ; the more we know the more fantastic the world becomes and the profounder the surrounding darkness.” Aldous Leonard Huxley “The most exciting phrase to hear in science, the one that heralds new discoveries, is not ’Eureka !’ but ’That’s funny...’ ” Isaac Asimov Fran¸cois Bianco Thin epitaxial ferromagnetic metal films on GaAs(001) for spin

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