1. Ferromagnetism in Diluted Magnetic Semiconductor Single Electron Transistors
Joaquín Fernández-Rossier (1) and L. Brey (2)
Dept. Física Aplicada, Univ de Alicante,Spain
ICMM (CSIC), Madrid, Spain
2004 American Physical Society March Meeting, Montreal

2. Ferromagnetism in Diluted Magnetic Semiconductor Single Electron Transistors
Joaquín Fernández-Rossier (1) and L. Brey (2)
Dept. Física Aplicada, Univ de Alicante,Spain
ICMM (CSIC), Madrid, Spain
Gate
Insulator
Gate
Insulator
+1 electron
Condmat/042140
1st Meeting of NanoSpain, San Sebastian, March 2004

3. Background

4. 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

5. Gating magnetism in 2D DMS FET
H. OHNO et al., Nature 408, 944 (2000)
Change of carrier
Density->
-> Change of Tc

6. Gating magnetism in 2D DMS FET
H. OHNO et al., Nature 408, 944 (2000)
Change of carrier
Density->
-> Change of Tc
FIRST TIME:
Reversible Isothermal Electric Control (on and off) of Ferromagnetism

7. Gating magnetism in 2D DMS FET
H. OHNO et al., Nature 408, 944 (2000)
Change of carrier
Density->
-> Change of Tc
But ....modest change in Tc because p<<p

8. Our Proposal: Electric control of magnetism in a single electron transistor diluted magnetic semiconductor dot
VG=0
Gate
Insulator
Q= 0e
5-10 nm
(Cd,Mn)Te quantum dot
J. Fernández-Rossier and L. Brey, cond-mat/

9. Our Proposal: Electric control of magnetism in a single electron transistor diluted magnetic semiconductor dot
VG>0
Gate
Insulator
Q=-1e
5-10 nm
(Cd,Mn)Te quantum dot
J. Fernández-Rossier and L. Brey, cond-mat/

10. 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

11. Possible with state of the art technique
(II,Mn)VI quantum dots
II-VI single electron transistor
P. S. Dorozhkin et al., Phys. Rev. B 68, (2003)
A. A. Maksimov et al., Phys. Rev. B 62, R7767–R7770 (2000)
CdSe nanocrystal (5.5 nm diameter)
Klein et al, Nature 389, 699 (1997)

12. Theory

13. Exchange interactions: superexchange vs carrier mediated
Exchange (RKKY)
Superexchange
Only 1st neighbours
Antiferromagnetic

14. Mean Field theory for ferromagnetism in DMS
BULK EG EF
Dietl et al.,
Science 287, 1019 (2000)
FM:Competition between exchange and entropy

15. Mean Field theory for ferromagnetism in DMS
DOT
(Cd0.99Mn0.01)Te
Quantum dot
7 nm
6 nm 2 1 1 2

16. Results: Swichting magnetism on and off with 1 electron
Sample to sample
dispersion
Average over configurations
25 Mn spins
5000 atoms
From S=0 to S=50
(Cd0.99Mn0.01)Te,Quantum dot, 5x6x7 nm

17. Injecting electrons one by one
Q=0 <M>=0
Q=1e <M> large
Q=2e
<M> small

18. Magnetization vs Temperature Odd Even
Survives at 6 Kelvin:
Much Higher than
(for n-doped) bulk
Figure 1 paper

19. Conclusions
Ferromagnetism induced by a single electron in DMS quantum dot
Strong odd-even effect ->total electric control of magnetism
Huge enhancement of Tc in 0 Dimensions
Gate
Insulator

20. Coming soon... Going nano: doping single Mn12ac molecule Gate
Insulator
Mn12
J. Fernández-Rossier
J. Pérez-Jiménez
J. J. Palacios

21. Nanoscience in Alicante

22. Nanoscience in Alicante
Nickel Nanocontacts
Small BMR
POSTER Nanoelectronics 09

23. Nanoscience in Alicante
Join effort: theory, simulation and experiment, physics and chemistry,UA + ICMM
Nanocontacts, Molecular Electronics, nanomagnetism, spintronics, polymer optics:
Molecular Dynamics (M. Caturla)
Ab initio quantum transport and
Model 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)