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Ferromagnetism in Diluted Magnetic Semiconductor Single Electron Transistors
Joaquín Fernández-Rossier (1) and L. Brey (2)
(1) Dept. Física Aplicada, Univ de Alicante,Spain(2) ICMM (CSIC), Madrid, Spain
2004 American Physical Society March Meeting, Montreal
Ferromagnetism in Diluted Magnetic Semiconductor Single Electron Transistors
Joaquín Fernández-Rossier (1) and L. Brey (2)
(1) Dept. Física Aplicada, Univ de Alicante,Spain(2) ICMM (CSIC), Madrid, Spain
1st Meeting of NanoSpain, San Sebastian, March 2004
www.ua.es/personal/jfrossier
Condmat/042140
GateInsulator
GateInsulator
+1 electron
Background
Diluted Magnetic Semiconductors:
materials for spintronics• Standard semiconductors doped with transition metal atoms: (Ga0.95,Mn0.05)As, (Cd0.99,Mn0.01)Te
• Mn provides local spins (d electrons) (S=2.5)• Ferromagnetism: induced by itinerant carriers
– Provided by Mn (example: (III,Mn)V)– Provided by other impurities (ex. (II,Mn)VI:N)– Injected electrically (field effect Transistor)
Paramagnetic Ferromagnetic
Gating magnetism in 2D DMS FET
H. OHNO et al., Nature 408, 944 (2000)
Change of carrierDensity->
-> Change of Tc
Gating magnetism in 2D DMS FET
H. OHNO et al., Nature 408, 944 (2000)
Change of carrierDensity->
-> Change of Tc
FIRST TIME:
Reversible Isothermal Electric Control (on and off) of
Ferromagnetism
Gating magnetism in 2D DMS FET
H. OHNO et al., Nature 408, 944 (2000)
Change of carrierDensity->
-> Change of Tc
But ....modest change in Tc because p<<p
GateInsulator
Q= 0e
VG=0
(Cd,Mn)Te quantum dot
5-10 nm
Our Proposal:Electric control of magnetism in a single
electron transistor diluted magnetic semiconductor dot
J. Fernández-Rossier and L. Brey, cond-mat/0402140
5-10 nm
VG>0
Q=-1e
GateInsulator
(Cd,Mn)Te quantum dot
Our Proposal:Electric control of magnetism in a single
electron transistor diluted magnetic semiconductor dot
J. Fernández-Rossier and L. Brey, cond-mat/0402140
Why?• From (In,Mn)As to (Cd,Mn)Te: p=n=0,
n=1e can make a difference
• From 2D to 0D:
– Increasing Tc
– Odd-even effects
– engineering wave function
• From holes to electrons: for simplicity
• Possible with state of the art
(II,Mn)VI quantum dots
P. S. Dorozhkin et al., Phys. Rev. B 68, 195313 (2003)A. A. Maksimov et al., Phys. Rev. B 62, R7767–R7770 (2000)
II-VI single electron
transistor
Klein et al, Nature 389, 699 (1997)
CdSe nanocrystal (5.5 nm diameter)
Possible with state of the art technique
Theory
Exchange interactions: superexchange vs carrier
mediated
21 MMJH AFSE
•Only 1st neighbours•Antiferromagnetic
Superexchange Carrier mediated Exchange (RKKY)
21 MMJH RKKYRKKY
i
iiheheex MrSJH
,),(
Mean Field theory for ferromagnetism in DMS
21 MMJH AFSE
i
iiheheex MrSJH
,),(
EG
EF
FM:Competition between exchange and entropy
Dietl et al.,Science 287, 1019 (2000)
BULK
Mean Field theory for ferromagnetism in DMS
DOT (Cd0.99Mn0.01)TeQuantum dot
7 n
m
6 nm
1
2
21
iifniAF
ninieinin
e
nnne
MMJ
MrrJ
EH
)(
','
*
´,´,0
2
Results: Swichting magnetism on and off with 1
electron
(Cd0.99Mn0.01)Te,Quantum dot, 5x6x7 nm
Average over
configurations
Sample to sample
dispersion
25 Mn spins5000 atomsFrom S=0 to S=50
Injecting electrons one by one
Q=0 <M>=0 Q=1e <M> large
Q=2e<M> small
Magnetization vs Temperature
Odd Even
Figure 1 paperSurvives at 6 Kelvin:Much Higher than (for n-doped) bulk
Conclusions
1. Ferromagnetism induced by a single electron in DMS quantum dot
2. Strong odd-even effect ->total electric control of magnetism
3. Huge enhancement of Tc in 0 Dimensions
GateInsulator
Coming soon...Going nano: doping single Mn12ac molecule
GateInsulator
Mn12
J. Fernández-RossierA. J. Pérez-JiménezJ. J. Palacios
Nanoscience in Alicante
Nanoscience in Alicante
Nickel NanocontactsSmall BMRPOSTER Nanoelectronics 09
Nanoscience in Alicante
Nanocontacts, Molecular Electronics, nanomagnetism, spintronics, polymer optics:•Molecular Dynamics (M. Caturla)•Ab initio quantum transport andModel Hamiltonian Theory (J.J. Palacios, E. Louis, E. San Fabian, A. J. Jiménez, J. A. Verges, G. Chiappe, JFR)•Experiments (C. Untied)•Experiments (M. Diez)
Join effort: theory, simulation and experiment, physics and chemistry,UA + ICMM