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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.

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Presentation on theme: "Ferromagnetism in Diluted Magnetic Semiconductor Single Electron Transistors Joaquín Fernández-Rossier (1) and L. Brey (2) (1)Dept. Física Aplicada, Univ."— Presentation transcript:

1 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

2 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 Condmat/ Gate Insulator Gate Insulator +1 electron

3 Background

4 Diluted Magnetic Semiconductors: materials for spintronics Standard semiconductors doped with transition metal atoms: (Ga 0.95,Mn 0.05 )As, (Cd 0.99,Mn 0.01 )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) ParamagneticFerromagnetic

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

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


8 Gate Insulator Q= 0e V G =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/

9 5-10 nm V G >0 Q=-1e Gate Insulator (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/

10 Why? From (In,Mn)As to (Cd,Mn)Te: p=n=0, n=1e can make a difference From 2D to 0D: – Increasing T c –Odd-even effects –engineering wave function From holes to electrons: for simplicity Possible with state of the art

11 (II,Mn)VI quantum dots P. S. Dorozhkin et al., Phys. Rev. B 68, (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

12 Theory

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

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

15 Mean Field theory for ferromagnetism in DMS DOT (Cd 0.99 Mn 0.01 )Te Quantum dot 7 nm 6 nm

16 Results: Swichting magnetism on and off with 1 electron (Cd 0.99 Mn 0.01 )Te,Quantum dot, 5x6x7 nm Average over configuration s Sample to sample dispersion 25 Mn spins 5000 atoms From S=0 to S=50

17 Injecting electrons one by one Q=0 =0Q=1e largeQ=2e small

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

19 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 Gate Insulator

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

21 Nanoscience in Alicante

22 Nickel Nanocontacts Small BMR POSTER Nanoelectronics 09

23 Nanoscience in Alicante 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) Join effort: theory, simulation and experiment, physics and chemistry,UA + ICMM


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