regensburg, 26.1.091 curie point singularity in gamnas institute of physics of the academy of...

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 ?

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GaMnAs, made in PragueGaMnAs, made in Prague

• substrate temperature • surface morphology• As stoichiometric• sample thicknesssample thickness

arbitrarily thick 2D ?

~yes (100 nm, 13% Mn)

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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)

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GaMnAs, made in PragueGaMnAs, made in Prague

• substrate temperature • surface morphology• As stoichiometric• sample thicknesssample thickness• annealingannealing

100 nm, 13% Mn

TC ~ 140 K !

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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

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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 ?

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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

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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 !

suppressed by B, disorder, ...

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• 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)

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• 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

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• 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

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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 !