1. Regensburg, 26.1.091 Curie point singularity in GaMnAs 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 Vít Novák, et al.

2. Regensburg, 26.1.092 GaMnAs, made in Prague growth temperature surface morphology stoichimetry / As overpressure sample thickness optimal annealing

3. Regensburg, 26.1.093 GaMnAs, made in Prague J. Appl. Phys. 102, 083536 (2007) growth temperaturegrowth temperature changes ?

4. Regensburg, 26.1.094 GaMnAs, made in Prague growth temperature surface morphologysurface morphology 2D / 3D ? 2D 3D non-rotating

5. Regensburg, 26.1.095 GaMnAs, made in Prague 2D 3D growth temperature surface morphologysurface morphology rotating (phase locked image)

6. Regensburg, 26.1.096 GaMnAs, made in Prague growth temperature surface morphologysurface morphology

7. Regensburg, 26.1.097 GaMnAs, made in Prague 3D 2D growth temperature surface morphologysurface morphology also: Campion et al, J. Mater. Sci. 15, 727 (2004)

8. Regensburg, 26.1.098 GaMnAs, made in Prague 3D 2D As:Ga=3:1 As:Ga=1:1 growth temperature surface morphology As pressureAs pressure

9. Regensburg, 26.1.099 GaMnAs, made in Prague 176K (11% Mn, 35 nm) growth temperaturegrowth temperature surface morphologysurface morphology As stoichiometricAs stoichiometric

10. Regensburg, 26.1.0910 GaMnAs, made in Prague substrate temperature surface morphology As stoichiometric sample thicknesssample thickness arbitrarily thick 2D ?

11. Regensburg, 26.1.0911 GaMnAs, made in Prague substrate temperature surface morphology As stoichiometric sample thicknesssample thickness arbitrarily thick 2D ? ~yes (100 nm, 13% Mn)

12. Regensburg, 26.1.0912 GaMnAs, made in Prague substrate temperature surface morphology As stoichiometric sample thicknesssample thickness arbitrarily thick 2D ? But ! :  300K =28  -1 cm -1  5K =0.05   cm   T C = 0 K ~yes (100 nm, 13% Mn)

13. Regensburg, 26.1.0913 GaMnAs, made in Prague substrate temperature surface morphology As stoichiometric sample thicknesssample thickness annealingannealing 100 nm, 13% Mn T C ~ 140 K !

14. Regensburg, 26.1.0914 GaMnAs, made in Prague substrate temperature surface morphology As stoichiometric sample thicknesssample thickness annealingannealing 100 nm, 13% Mn T C ~ 175 K !! thinned (25 nm) annealed +

15. Regensburg, 26.1.0915 GaMnAs, made in Prague substrate temperature surface morphology As stoichiometric sample thicknesssample thickness annealingannealing 100 nm, 13% Mn T C ~ 150 K !!! thinned (25 nm) annealed + part. annealed + inhomogeneity unlikely, thermal degradation

16. Regensburg, 26.1.0916 GaMnAs, made in Prague substrate temperature surface morphology As stoichiometric sample thickness optimal annealingoptimal annealing optimum time

17. Regensburg, 26.1.0917 GaMnAs, made in Prague substrate temperature surface morphology As stoichiometric sample thickness optimal annealingoptimal annealing optimum time lower temperature ?

18. Regensburg, 26.1.0918 GaMnAs, made in Prague substrate temperature surface morphology As stoichiometric sample thickness optimal annealingoptimal annealing optimum time optimum temperature

19. Regensburg, 26.1.0919 GaMnAs, made in Prague substrate temperaturesubstrate temperature surface morphologysurface morphology As stoichiometricAs stoichiometric sample thicknesssample thickness optimal annealingoptimal annealing -89.2 °C = 184K ! (RT in Antarctica, Vostok, 21 July 1983) 176K 12.5% Mn, 23 nm 186K

20. Regensburg, 26.1.0920 Curie point singularity Matsukura et al., Dietl et al., … magnetizationmagnetization resistivityresistivity

21. Regensburg, 26.1.0921 Curie point singularity EuO Eu 0.95 Gd 0.05 S Penney et al., Phys. Rev. B 5, 3669 (1972), … Haas, Magnetic semiconductors (1970) ordered magnetic semiconductorsordered magnetic semiconductors sharp critical behavior of  at T C

22. Regensburg, 26.1.0922 Curie point singularity disordered DMSsdisordered DMSs broad peak near T C the better material – the broader peak !

23. Regensburg, 26.1.0923 Curie point singularity magnetizationmagnetization resistivityresistivity

24. Regensburg, 26.1.0924 Curie point singularity d  /dTd  /dT resistivityresistivity

25. Regensburg, 26.1.0925 d  /dT mostly cusp-like ! Curie point singularity magnetizationmagnetization resistivityresistivity d  /dTd  /dT

26. Regensburg, 26.1.0926 Curie point singularity effect of annealingeffect of annealing

27. Regensburg, 26.1.0927 Curie point singularity annealed/good samplesannealed/good samples

28. Regensburg, 26.1.0928 Curie point singularity scalingscaling

29. Regensburg, 26.1.0929 Curie point singularity what’s behindwhat’s behind nonmagnetic scattering, ~ T

30. Regensburg, 26.1.0930 Curie point singularity what’s behindwhat’s behind  =    – f(M 2 ) scattering on uncorrelated Mn: nonmagnetic scattering, ~ T

31. Regensburg, 26.1.0931 Curie point singularity what’s behindwhat’s behind  =    – f(M 2 ) scattering on uncorrelated Mn, nonmagnetic scattering, ~ T crit. behavior also for T>T C

32. Regensburg, 26.1.0932 Curie point singularity what’s behindwhat’s behind  =    – f(M 2 ) scattering on uncorrelated Mn, nonmagnetic scattering, ~ T crit. behavior also for T>T C ! suppressed by B, disorder,...

33. Regensburg, 26.1.0933 what’s behindwhat’s behind de Gennes&Friedel (1958) singular Scattering from correlated spin-fluctuations Eu 0.95 Gd 0.05 S Curie point singularity Fisher&Langer (1968)

34. Regensburg, 26.1.0934 what’s behindwhat’s behind singular Curie point singularity Scattering from correlated spin-fluctuations Fisher&Langer (1968) max. above T C

35. Regensburg, 26.1.0935 what’s behindwhat’s behind Nickel singular Curie point singularity Scattering from correlated spin-fluctuations Fisher&Langer (1968) max. above T C

36. Regensburg, 26.1.0936 what’s behindwhat’s behind Curie point singularity GaMnAs : ! resembles metals

37. Regensburg, 26.1.0937 Curie point singularity experimental way to T Cexperimental way to T C 5 nm, 7% Mn 100 nm, 1.7% Mn for weak M in devices

38. Regensburg, 26.1.0938 Summary T C still increasing (although hardly) GaMnAs close to metals (but still semiconducting) cusp singularity on d  /dT (instead of  experimental way to T C Thank you !