Magic triangle Magic triangle M a te r i a l s s ci en c e e p i ta x y , s e l f o rg a n iz e d g ro w th o r g a n i c s ynth e s is i m p l a nt a ti o n, is o t o p e p u rifi c a t io n a t om a n d m o l e c u le m a n i p u la t io n n a no l i th o g ra p h y , n a no p ri n t i n g b e a m a n d s c a n n in g pro b e s . .. .
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Magic triangle - KFKI · 1700 1710 1.49 K 1.65 1.88 2.05 2.19 2.82 2.97 b 4.2 K-1V Combined: electrostatic gate + illumination in pin diode (ferro-LED) Combined: electrostatic gate
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Magic triangleMagic triangle
Materials science
epitaxy, self organized growth
organic synthesis
implantation, isotope purification
atom and molecule manipulation
nanolithography, nanoprinting
beam and scanning probes
....
Magic triangleMagic triangle
Materials science
epitaxy, self organized growth
organic synthesis
implantation, isotope purification
atom and molecule manipulation
nanolithography, nanoprinting
beam and scanning probes
....
Physics of complex systems
exotic ground states and quasiparticles phase and statistical
transformations complex dynamics ….
Magic triangleMagic triangle
Materials science
epitaxy, self organized growth
organic synthesis
implantation, isotope purification
atom and molecule manipulation
nanolithography, nanoprinting
beam and scanning probes
....
Physics of complex systems
exotic ground states and quasiparticles phase and statistical
transformations complex dynamics ….
High tech/IT photonics (optoelectronics) MEMS, NEMS electronics, magnetoelectronics spintronics ….
• New information carrier - electron � photon, flux (SQUID loops), vortex (type II superconductors); - spin rather than charge ...
• New principle of device operation quantum devices, spin transistors, ...
• New architecture - physical, chemical and biological processes - quantum computing
• Integration of functions, not only elements => Spintronics
SPINTRONICS exploiting spin, not only charge SPINTRONICS exploiting spin, not only charge
rational: spin robust to external perturbations
• Storing and processing of classical information
• Storing and processing of quantum information
• Sensing magnetic field
Giant magnetoresistance (GMR)in ferromagnetic metal multilayersGiant magnetoresistance (GMR)
in ferromagnetic metal multilayers
A. Fert et al., P. Gruenberg et al., S. Parkin et al., 1988-91J. Barnaś et al. (theory)
4.2 K
Information readingInformation reading GMR/TMR sensors IBM 1997- GMR/TMR sensors IBM 1997- GMR
TMR
Magnetic random access memory(MRAM)
Magnetic random access memory(MRAM)
Infineon, Motorola, 256 kb
• non-volatile• fast (50 ns)• reliable• radiation hardness• ....
Difficulties:• thin oxide, 1.2 nm• large writing currents• ...
Why to do not combine complementary properties andfunctionalities of semiconductor and magnetic materialsystems?
• hybrid structures -- overlayers or inclusions of ferromagnetic metals =>
source of stray fields and spin-polarized carriers -- soft ferromagnets => local field amplifiers -- hard ferromagnets => local field generators (cf. J. Kossut, ILC, Budapest’02)
• ferromagnetic semiconductors
Spintronics – material aspectsSpintronics – material aspects
• magnetic semiconductors short-range ferromagnetic super- or double exchange EuS, ZnCr2Se4, La1-xSrxMnO3, ...
• diluted magnetic semiconductors long-range hole-mediated ferromagnetic exchange IV-VI: p-Pb1-x-yMnxSnyTe (Story et al.’86) III-V: In1-x-MnxAs (Munekata et al.’89,’92) Ga1-x-MnxAs (Ohno et al.’96) TC ≈≈≈≈ 100 K for x = 0.05 II-VI: Cd1-xMnxTe/Cd1-x-yZnxMgyTe:N QW (Cibert et al.’97, Kossacki et al.’99) Zn1-xMnxTe:N (Ferrand et al.’99) Be1-xMnxTe:N (Hansen et al.’01)
III-V and II-VI DMS:quantum nanostructures and ferromagnetism combine
Spin injection in p-i-n(Ga,Mn)As /(In,Ga)As/GaAs diode (spin-LED)
Spin injection in p-i-n(Ga,MnMn)As /(In,Ga)As/GaAs diode (spin-LED)
Ohno et al., Nature ‘99
Pola
rizat
ion
(%)
The nature of the Mn state and its couplingto carriers
The nature of the Mn state and its couplingto carriers
Mn: 3d54s2
II-VI: Mn electrically neutral (3d5, S = 5/2) –doping by acceptors necessary
III-V: Mn acts as source of spins and holes
• large p-d hybridization and large intra-site Hubbard U => Kondo hamiltonian H = -ββββNoSs => large Mn-hole exchange
-- (Ga,Mn)As: ββββNo ≈≈≈≈ - 1.2 eV (Szczytko et al., Okabayashi et al.) -- (Zn,Mn)Te: ββββNo ≈≈≈≈ - 1.0 eV (Twardowski et al.)• no s-d hybridization => small Mn-electron exchange
ααααNo ≈≈≈≈ 0.2 eV (Gaj et al.)
Mean-field Zener modelMean-field Zener model
Which form of Mn magnetization minimizes F[M(r)]?
F = FMn [M(r)] + Fholes [M(r)]
M(r) ≠ 0 for H= 0 at T < TC
if M(r) uniform => ferromagnetic orderotherwise => modulated magnetic structure
nholes << Nspins ���� Zener ≡≡≡≡RKKY
k
Curie temperature in p-Ga1-xMnxAstheory vs. experiment
Curie temperature in p-Ga1-xMnxAstheory vs. experiment
• Anomalous Halleffect ���� puncertain
• Omiya et al.: 27 T, 50 mK
• Theory: TC > 300 K for x > 0.1 and large p
0 1 2 3 4 50
50
100
150
200
THEORY, x = 0.05
Oiwa et al.Van Esch et al.Matsukura et al.Shimizu et al.
Omiya et al.
Ga1-xMnxAs
CU
RIE
TEM
PER
ATU
RE
[K]
HOLE CONCENTRATION [1020 cm-3]
T.D. et al., PRB’01
Tuning of magnetic ordering byelectrostatic gates (ferro-FET)
Tuning of magnetic ordering byelectrostatic gates (ferro-FET)
H. Ohno, .., T.D., ...Nature ‘00
Ferromagnetic temperature in2D p-Cd1-xMnxTe QW and 3D Zn1-xMnxTe:N
Ferromagnetic temperature in2D p-Cd1-xMnxTe QW and 3D Zn1-xMnxTe:N
0.01 0.05 0.1
1
10
1
10
2D
3D
Ferr
omag
netic
Tem
p. T
F / x ef
f (K)
Fermi wave vector k (A-1)0.2
ρρρρ(k)
ρρρρ(k)
ρρρρ(k)
k
k
k
3D
2D
1D
H. Boukari, ..., T.D., PRL’02 D. Ferrand, ... T.D., ... PRB’01
1020 cm-31018 1019
1700 1710
1.49 K1.651.872.052.19
2.80
3.03
4.2 K0V
PL In
tens
ity (a
.u.)
Energy (meV)
a
1700 1710
1.49 K1.651.88
2.05
2.19
2.822.97
b4.2 K
-1V
V
QWbarriers
p doped
n doped
undoped
Control byelectrostatic gatein a pin diode –
ferro-LED
Control byelectrostatic gatein a pin diode –
ferro-LED
Hole liquid Depleted
Ev
Ec
EF
V
PRL’02
Photoluminescence
1700 1710
1.49 K1.651.872.052.19
2.80
3.03
4.2 K0V
PL In
tens
ity (a
.u.)
Energy (meV)
a
1700 1710
1.49 K1.651.88
2.05
2.19
2.822.97
b4.2 K
-1V
Combined: electrostaticgate + illumination
in pin diode (ferro-LED)
Combined: electrostaticgate + illumination
in pin diode (ferro-LED)
Hole liquid Depleted
V
QW
1700 1710
0 V1.5 K
Ev
Ec
EFV
illum
inat
ion
Ferro- diode:electric field and light tuned ferromagnetism
PRL ‘02
Optical tuning of magnetization - pip diodeOptical tuning of magnetization - pip diode