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)

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