regensburg, 26.1.091 curie point singularity in gamnas institute of physics of the academy of...
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Regensburg, 26.1.09 1
Curie point singularity in GaMnAsCurie 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, 26.1.09 2
GaMnAs, made in PragueGaMnAs, made in Prague
• growth temperature • surface morphology• stoichimetry / As overpressure• sample thickness• optimal annealing
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GaMnAs, made in PragueGaMnAs, made in Prague
J. Appl. Phys. 102, 083536 (2007)
• growth temperaturegrowth temperature
changes ?
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GaMnAs, made in PragueGaMnAs, made in Prague
• growth temperature • surface morphologysurface morphology
2D / 3D ? 2D
3D
non-rotating
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GaMnAs, made in PragueGaMnAs, made in Prague
2D
3D
• growth temperature • surface morphologysurface morphology
rotating (phase locked image)
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GaMnAs, made in PragueGaMnAs, made in Prague
• growth temperature • surface morphologysurface morphology
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GaMnAs, made in PragueGaMnAs, made in Prague
3D
2D
• growth temperature • surface morphologysurface morphology
also: Campion et al, J. Mater. Sci. 15, 727 (2004)
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GaMnAs, made in PragueGaMnAs, made in Prague
3D
2D
As:Ga=3:1As:Ga=1:1
• growth temperature • surface morphology• As pressureAs pressure
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GaMnAs, made in PragueGaMnAs, made in Prague
176K
(11% Mn, 35 nm)
• growth temperature growth temperature • surface morphologysurface morphology• As stoichiometric As stoichiometric
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GaMnAs, made in PragueGaMnAs, made in Prague
• substrate temperature • surface morphology• As stoichiometric• sample thicknesssample thickness
arbitrarily thick 2D ?
Regensburg, 26.1.09 11
GaMnAs, made in PragueGaMnAs, made in Prague
• substrate temperature • surface morphology• As stoichiometric• sample thicknesssample thickness
arbitrarily thick 2D ?
~yes (100 nm, 13% Mn)
Regensburg, 26.1.09 12
GaMnAs, made in PragueGaMnAs, made in Prague
• substrate temperature • surface morphology• As stoichiometric• sample thicknesssample thickness
arbitrarily thick 2D ?
But ! : 300K=28 -1cm-1
5K=0.05 cm
TC = 0 K
~yes (100 nm, 13% Mn)
Regensburg, 26.1.09 13
GaMnAs, made in PragueGaMnAs, made in Prague
• substrate temperature • surface morphology• As stoichiometric• sample thicknesssample thickness• annealingannealing
100 nm, 13% Mn
TC ~ 140 K !
Regensburg, 26.1.09 14
GaMnAs, made in PragueGaMnAs, made in Prague
• substrate temperature • surface morphology• As stoichiometric• sample thicknesssample thickness• annealingannealing
100 nm, 13% Mn
TTCC ~ 175 K !! ~ 175 K !!
thinned (25 nm)thinned (25 nm)
annealedannealed++
Regensburg, 26.1.09 15
GaMnAs, made in PragueGaMnAs, made in Prague
• substrate temperature • surface morphology• As stoichiometric• sample thicknesssample thickness• annealingannealing
100 nm, 13% Mn
TTCC ~ 150 K !!! ~ 150 K !!!
thinned (25 nm)thinned (25 nm)
annealedannealed++
part. annealedpart. annealed++
inhomogeneity unlikely, thermal degradation
Regensburg, 26.1.09 16
GaMnAs, made in PragueGaMnAs, made in Prague
• substrate temperature • surface morphology• As stoichiometric• sample thickness• optimal annealingoptimal annealing
optimum time
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GaMnAs, made in PragueGaMnAs, made in Prague
• substrate temperature • surface morphology• As stoichiometric• sample thickness• optimal annealingoptimal annealing
optimum time
lower temperature ?
Regensburg, 26.1.09 18
GaMnAs, made in PragueGaMnAs, made in Prague
• substrate temperature • surface morphology• As stoichiometric• sample thickness• optimal annealingoptimal annealing
optimum time
optimum temperature
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GaMnAs, made in PragueGaMnAs, made in Prague
• substrate temperature substrate temperature • surface morphologysurface morphology• As As stoichiometrstoichiometricic• sample thicknesssample thickness• optimal annealingoptimal annealing
-89.2 °C = 184K ! (RT in Antarctica, Vostok, 21 July 1983)
176K
12.5% Mn, 23 nm12.5% Mn, 23 nm
186K
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Curie point singularityCurie point singularity
Matsukura et al., Dietl et al., …
• magnetizationmagnetization• resistivityresistivity
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Curie point singularityCurie point singularity
EuO
Eu0.95Gd0.05S
Penney et al., Phys. Rev. B 5, 3669 (1972), …
Haas, Magnetic semiconductors (1970)
• ordered magnetic semiconductorsordered magnetic semiconductors
sharp critical behavior of at TC
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Curie point singularityCurie point singularity• disordered DMSsdisordered DMSs
broad peak near TC
the better material – the broader peak !
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Curie point singularityCurie point singularity
• magnetizationmagnetization• resistivityresistivity
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Curie point singularityCurie point singularity
• dd/dT/dT• resistivityresistivity
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d/dT mostly cusp-like !
Curie point singularityCurie point singularity
• magnetizationmagnetization• resistivityresistivity• dd/dT/dT
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Curie point singularityCurie point singularity
• effect of annealingeffect of annealing
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Curie point singularityCurie point singularity
• annealed/good samplesannealed/good samples
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Curie point singularityCurie point singularity
• scalingscaling
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Curie point singularityCurie point singularity
• what’s behindwhat’s behind
nonmagnetic scattering, ~ T
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Curie point singularityCurie point singularity
• what’s behindwhat’s behind
= – f(M2)
scattering on uncorrelated Mn:
nonmagnetic scattering, ~ T
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Curie point singularityCurie point singularity
• what’s behindwhat’s behind
= – f(M2)
scattering on uncorrelated Mn,
nonmagnetic scattering, ~ T
crit. behavior also for T>TC
Regensburg, 26.1.09 32
Curie point singularityCurie point singularity
• what’s behindwhat’s behind
= – f(M2)
scattering on uncorrelated Mn,
nonmagnetic scattering, ~ T
crit. behavior also for T>TC !
suppressed by B, disorder, ...
Regensburg, 26.1.09 33
• what’s behindwhat’s behind
00~)( SSSST ii
de Gennes&Friedel (1958)
singular
Scattering from correlated spin-fluctuations
Eu0.95Gd0.05S
Curie point singularityCurie point singularity
Fisher&Langer (1968)
Regensburg, 26.1.09 34
• what’s behindwhat’s behind
singular
Curie point singularityCurie point singularity
00~)( SSSST ii
Scattering from correlated spin-fluctuations
Fisher&Langer (1968)
max. above TC
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• what’s behindwhat’s behind
Nickel
singular
Curie point singularityCurie point singularity
00~)( SSSST ii
Scattering from correlated spin-fluctuations
Fisher&Langer (1968)
max. above TC
Regensburg, 26.1.09 36
• what’s behindwhat’s behind
Curie point singularityCurie point singularity
GaMnAs : !
resembles metals
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Curie point singularityCurie point singularity
• experimental way experimental way to Tto TCC
5 nm, 7% Mn5 nm, 7% Mn
100 nm, 1.7% Mn100 nm, 1.7% Mn
for weak M
in devices
Regensburg, 26.1.09 38
SummarySummary
• TC still increasing (although hardly)
• GaMnAs close to metals (but still semiconducting)
• cusp singularity on d/dT (instead of
• experimental way to TC
• Thank you !