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

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 www.ua.es/personal/jfrossier Condmat/042140 1st Meeting of NanoSpain, San Sebastian, March 2004

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 carrier Density-> -> Change of Tc

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

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

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/0402140

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/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

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, 195313 (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)

Theory

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

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

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

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

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

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

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

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

Nanoscience in Alicante

Nanoscience in Alicante Nickel Nanocontacts Small BMR POSTER Nanoelectronics 09

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)