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

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.


GaMnAs, made in PragueGaMnAs, made in Prague

• growth temperature • surface morphology• stoichimetry / As overpressure• sample thickness• optimal annealing



J. Appl. Phys. 102, 083536 (2007)

• growth temperaturegrowth temperature

changes ?



• growth temperature • surface morphologysurface morphology

2D / 3D ? 2D

3D

non-rotating



2D

3D


rotating (phase locked image)






3D

2D


also: Campion et al, J. Mater. Sci. 15, 727 (2004)



3D

2D

As:Ga=3:1As:Ga=1:1

• growth temperature • surface morphology• As pressureAs pressure



176K

(11% Mn, 35 nm)

• growth temperature growth temperature • surface morphologysurface morphology• As stoichiometric As stoichiometric



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

arbitrarily thick 2D ?





~yes (100 nm, 13% Mn)





But ! : 300K=28 -1cm-1

5K=0.05 cm

TC = 0 K

~yes (100 nm, 13% Mn)



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

100 nm, 13% Mn

TC ~ 140 K !




100 nm, 13% Mn

TTCC ~ 175 K !! ~ 175 K !!

thinned (25 nm)thinned (25 nm)

annealedannealed++




100 nm, 13% Mn

TTCC ~ 150 K !!! ~ 150 K !!!

thinned (25 nm)thinned (25 nm)

annealedannealed++

part. annealedpart. annealed++

inhomogeneity unlikely, thermal degradation



• substrate temperature • surface morphology• As stoichiometric• sample thickness• optimal annealingoptimal annealing

optimum time




optimum time

lower temperature ?




optimum time

optimum temperature



• 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


Curie point singularityCurie point singularity

Matsukura et al., Dietl et al., …

• magnetizationmagnetization• resistivityresistivity



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


Curie point singularityCurie point singularity• disordered DMSsdisordered DMSs

broad peak near TC

the better material – the broader peak !



• magnetizationmagnetization• resistivityresistivity



• dd/dT/dT• resistivityresistivity


d/dT mostly cusp-like !


• magnetizationmagnetization• resistivityresistivity• dd/dT/dT



• effect of annealingeffect of annealing



• annealed/good samplesannealed/good samples



• scalingscaling



• what’s behindwhat’s behind

nonmagnetic scattering, ~ T




= – f(M2)

scattering on uncorrelated Mn:





= – f(M2)

scattering on uncorrelated Mn,


crit. behavior also for T>TC




= – f(M2)

scattering on uncorrelated Mn,


crit. behavior also for T>TC !

suppressed by B, disorder, ...



00~)( SSSST ii

de Gennes&Friedel (1958)

singular

Scattering from correlated spin-fluctuations

Eu0.95Gd0.05S


Fisher&Langer (1968)



singular


00~)( SSSST ii



max. above TC



Nickel

singular


00~)( SSSST ii



max. above TC




GaMnAs : !

resembles metals



• 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


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 !

Documents

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