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Curie point singularity in GaMnAs

Curie point singularity in GaMnAs. Vít Novák, et al. Institute of Physics of the Academy of Sciences of the Czech Republic. Division of Solid State Physics. Department of Spintronics and Nanoelectronics. Theory : Jungwirth, Smr čka, Kučera, Sinova Technology & experiment :

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Curie point singularity in GaMnAs

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  1. Curie point singularity in GaMnAs Vít Novák, et al. Institute of Physics of the Academy of Sciences of the Czech Republic Division of Solid State Physics Department of Spintronics and Nanoelectronics Theory: Jungwirth, Smrčka, Kučera, Sinova Technology & experiment: Novák, Olejník, Cukr, Wunderlich

  2. GaMnAs, made in Prague • growth temperature • surface morphology • stoichimetry / As overpressure • sample thickness • optimal annealing

  3. GaMnAs, made in Prague • growth temperature changes ? J. Appl. Phys. 102, 083536 (2007)

  4. GaMnAs, made in Prague non-rotating • growth temperature • surface morphology 2D / 3D ? 2D 3D

  5. GaMnAs, made in Prague rotating (phase locked image) • growth temperature • surface morphology 2D 3D

  6. GaMnAs, made in Prague • growth temperature • surface morphology

  7. GaMnAs, made in Prague • growth temperature • surface morphology 3D 2D also: Campion et al, J. Mater. Sci. 15, 727 (2004)

  8. GaMnAs, made in Prague • growth temperature • surface morphology • As pressure 3D As:Ga=3:1 As:Ga=1:1 2D

  9. 176K GaMnAs, made in Prague • growth temperature • surface morphology • As stoichiometric (11% Mn, 35 nm)

  10. GaMnAs, made in Prague • substrate temperature • surface morphology • As stoichiometric • sample thickness arbitrarily thick 2D ?

  11. GaMnAs, made in Prague ~yes (100 nm, 13% Mn) • substrate temperature • surface morphology • As stoichiometric • sample thickness arbitrarily thick 2D ?

  12. GaMnAs, made in Prague ~yes (100 nm, 13% Mn) • substrate temperature • surface morphology • As stoichiometric • sample thickness arbitrarily thick 2D ? But ! : s300K=28 W-1cm-1 s5K=0.05 W-1cm-1 TC = 0 K

  13. GaMnAs, made in Prague • substrate temperature • surface morphology • As stoichiometric • sample thickness • annealing 100 nm, 13% Mn TC ~ 140 K !

  14. GaMnAs, made in Prague • substrate temperature • surface morphology • As stoichiometric • sample thickness • annealing 100 nm, 13% Mn thinned (25 nm) + annealed TC ~ 175 K !!

  15. GaMnAs, made in Prague • substrate temperature • surface morphology • As stoichiometric • sample thickness • annealing 100 nm, 13% Mn part. annealed + thinned (25 nm) + annealed TC ~ 150 K !!! inhomogeneity unlikely, thermal degradation

  16. GaMnAs, made in Prague • substrate temperature • surface morphology • As stoichiometric • sample thickness • optimal annealing optimum time

  17. GaMnAs, made in Prague • substrate temperature • surface morphology • As stoichiometric • sample thickness • optimal annealing optimum time lower temperature ?

  18. GaMnAs, made in Prague • substrate temperature • surface morphology • As stoichiometric • sample thickness • optimal annealing optimum time optimum temperature

  19. 186K 176K GaMnAs, made in Prague • substrate temperature • surface morphology • As stoichiometric • sample thickness • optimal annealing 12.5% Mn, 23 nm -89.2 °C = 184K ! (RT in Antarctica, Vostok, 21 July 1983)

  20. Curie point singularity • magnetization • resistivity Matsukura et al., Dietl et al., …

  21. Curie point singularity • ordered magnetic semiconductors sharp critical behavior of r at TC Eu0.95Gd0.05S EuO Haas, Magnetic semiconductors (1970) Penney et al., Phys. Rev. B 5, 3669 (1972), …

  22. Curie point singularity • disordered DMSs broad peak near TC the better material – the broader peak !

  23. Curie point singularity • magnetization • resistivity

  24. Curie point singularity • dr/dT • resistivity

  25. Curie point singularity • magnetization • resistivity • dr/dT dr/dT mostly cusp-like !

  26. Curie point singularity • effect of annealing

  27. Curie point singularity • annealed/good samples

  28. Curie point singularity • scaling

  29. Curie point singularity • what’s behind nonmagnetic scattering, ~ T

  30. Curie point singularity • what’s behind nonmagnetic scattering, ~ T scattering on uncorrelated Mn: r = r0– f(M2)

  31. Curie point singularity • what’s behind nonmagnetic scattering, ~ T scattering on uncorrelated Mn, r = r0– f(M2) crit. behavior also for T>TC

  32. Curie point singularity • what’s behind nonmagnetic scattering, ~ T scattering on uncorrelated Mn, r = r0– f(M2) crit. behavior also for T>TC ! suppressed by B, disorder, ...

  33. Curie point singularity • what’s behind Scattering from correlated spin-fluctuations de Gennes&Friedel (1958) Eu0.95Gd0.05S Fisher&Langer (1968) singular

  34. Curie point singularity • what’s behind Scattering from correlated spin-fluctuations Fisher&Langer (1968) max. above TC singular

  35. Curie point singularity • what’s behind Scattering from correlated spin-fluctuations Nickel Fisher&Langer (1968) max. above TC singular

  36. Curie point singularity • what’s behind ! GaMnAs : resembles metals

  37. Curie point singularity • experimental way to TC for weak M in devices 5 nm, 7% Mn 100 nm, 1.7% Mn

  38. Summary • TC still increasing (although hardly) • GaMnAs close to metals (but still semiconducting) • cusp singularity on dr/dT (instead of r) • experimental way to TC • Thank you !

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