Regensburg, 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.

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

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

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

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

Regensburg, GaMnAs, made in Prague growth temperature surface morphologysurface morphology

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

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

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

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

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

Regensburg, 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)

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

Regensburg, 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 +

Regensburg, 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

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

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

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

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

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

Regensburg, 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

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

Regensburg, Curie point singularity magnetizationmagnetization resistivityresistivity

Regensburg, Curie point singularity d  /dTd  /dT resistivityresistivity

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

Regensburg, Curie point singularity effect of annealingeffect of annealing

Regensburg, Curie point singularity annealed/good samplesannealed/good samples

Regensburg, Curie point singularity scalingscaling

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

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

Regensburg, 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

Regensburg, 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,...

Regensburg, 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)

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

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

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

Regensburg, 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

Regensburg, 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 !