From quantum mechanics to spintronics Ingrid Mertig - - PowerPoint PPT Presentation

From quantum mechanics to spintronics

Kyoto January 23, 2009

Ingrid Mertig Martin-Luther-Universität Halle, Germany

Outline

Kyoto January 23, 2009

• Ab initio calculations
• Tunneling magnetoresistance
• n the sub-nanometer scale
• Multiferroic interfaces and

magnetoelectric coupling

• Magnetic molecules
• Summary

Ab initio calculations

Green function method

Kyoto January 23, 2009

• Kohn-Sham equation
• Green’s function
• Dyson equation

N scaling!

The power of Green functions

Kyoto January 23, 2009

Surface Nanocontact

∞

Tunneling magnetoresistance

Thanks

Christian Heiliger Peter Zahn Bogdan Yavorsky Martin Gradhand Michael Czerner Martyna Pollock Wowa Maslyuk Peter Bose Igor Maznichenko Michael Fechner Steven Walczak Dima Fedorov

Peter Zahn Martin Gradhand Christian Heiliger

• M. Julliere, Phys. Lett. 54A, 225 (1975)
• J. S. Moodera et al., Phys. Rev. Lett. 74, 3273 (1995)

TMR =(gP - gAP)/ (gP+gAP)

TMR

Tunneling magnetoresistance

Kyoto January 23, 2009

Ab initio calculation – coherent limit

Kyoto January 23, 2009

Fe Fe EF

TMR > 1000 %

• W. H. Butler et al., Phys. Rev. B 63, 054416 (2001)
• G. Mathon et al., Phys. Rev. B 63, 220403(R) (2001)
• C. Heiliger et al., Phys. Rev. B 72, 180406(R) (2005)

MgO

Fe(001)

(Pinned layer)

MgO(001) Fe(001)

(Free layer)

2 nm

• S. Yuasa et al., Nature Materials 3, 868 (2004)

High quality MgO barriers

Kyoto January 23, 2009

Courtesy of S. Yuasa

Development of the TMR effect

Kyoto January 23, 2009

> 400 %

amorphous CoFeB

• S. Parkin, MRS Bulletin 31, 389 (2006)

as depoited: after annealing: 60% 350% TMR ratio

amorphous Fe electrodes MgO Febcc free electron-like reservoir Cu-bcc free electron like reservoir Cu-bcc

. . . . . .

Role of the electrodes

Kyoto January 23, 2009

MgO

1 2 3 4 5 6 0.0 0.2 0.7 0.8 0.9 1.0

number of crystalline Fe layers TMR ratio ∞ Fe

47% as deposited: 60%

TMR for amorphous Fe electrodes

Kyoto January 23, 2009

Δ1

majority electrons

Δ1

minority electrons

1 2 3 4 5 6 0.0 0.2 0.7 0.8 0.9 1.0

number of crystalline Fe layers TMR ratio ∞ Fe

TMR – 1ML of Fe and amorphous Fe electrodes

Kyoto January 23, 2009

after annealing: 350% 570%

1 2 3 4 5 6 0.0000 0.0005 0.0010 0.1 0.2 0.3

P AP

∞ Fe ∞ Fe number of crystalline Fe layers conductance density (1/ m ) Ωμ

2

Conductance for P and AP configuration

Kyoto January 23, 2009

• C. Heiliger et al., Phys. Rev. Lett. 99, 066804 (2007)
• M. Gradhand et al., Phys. Rev. B 77, 134403 (2008)

Δ1

majority electrons

Δ5

minority electrons

1 2 3 4 5 6 0.0000 0.0005 0.0010 0.1 0.2 0.3

P AP

∞ Fe ∞ Fe number of crystalline Fe layers conductance density (1/ m ) Ωμ

2

Conductance for P and AP configuration

Kyoto January 23, 2009

Δ1

majority electrons

Δ5 Δ5

minority electrons

• C. Heiliger et al., Phys. Rev. Lett. 99, 066804 (2007)
• M. Gradhand et al., Phys. Rev. B 77, 134403 (2008)

Amorphous versus free electron like electrodes

Kyoto January 23, 2009

• C. Heiliger et al., Phys. Rev. Lett. 99, 066804 (2007)
• M. Gradhand et al., Phys. Rev. B 77, 134403 (2008)

Multiferroic interfaces

Thanks

Christian Heiliger Peter Zahn Bogdan Yavorsky Martin Gradhand Michael Czerner Martyna Pollock Wowa Maslyuk Peter Bose Igor Maznichenko Michael Fechner Steven Walczak Dima Fedorov

Michael Fechner Sergey Ostanin Igor Maznichenko Arthur Ernst

Multiferroic interfaces

Magnetic layer Ferroelectric oxide

+ + + + +

• -
• -
• + + + + +

P

Kyoto January 23, 2009

M

BaTiO3

Magnetoelectric coupling

+ + + + +

• -
• + + + + +
• -
• P

M P M

Magnetisation Electrical polarisation

E

External electric field

B

External magnetic field

Kyoto January 23, 2009

One monolayer of Fe on BaTiO3

δ = z(O) – z(Kation)

• 0.07
• 0.03
• 0.05
• 0.08
• 0.09

0.02 0.08 0.09 0.08 0.09

Pup Pdown

Magnetic order of Fe on BaTiO3

ferromagnetic

• 0.07
• 0.03
• 0.05
• 0.08
• 0.09

0.02 0.08 0.09 0.08 0.09

Pup Pdown

Fe 2.91 μB Ti -0.10 μB O 0.10 μB Fe 2.97 μB Ti -0.07 μB O 0.09 μB

Charge transfer from Fe to Ti under switching

Kyoto January 23, 2009

Δq = 0.56 e ΔM = 0.13 μB Change of charge

• n the Fe layer:

Pup Pdown

• M. Fechner et al., PRB 78, 212406 (2008)

Charge transfer from Ti to Fe

Kyoto January 23, 2009

Ti Fe Fe Ti

Pup

• Pdown

Magnetic order in the Fe layer on BaTiO3

Kyoto January 23, 2009

T

c = 205 K

Fe2MLBa 2.38 μB Fe1ML 0.37 μB Fe2MLTi -2.71 μB

Pup Pdown

Fe2MLBa 2.18 μB Fe1ML 0.33 μB Fe2MLTi -2.36 μB

antiferrimagnetic

Structure: Fe in plane 2.79 Fe between planes 1.1

• M. Fechner et al., PRB 78, 212406 (2008)

Magnetic order in the Fe layer on BaTiO3

Kyoto January 23, 2009

Pup Pdown

Magnetoelectric coefficient:

Magnetic order in the Fe layer on BaTiO3

Kyoto January 23, 2009

Magnetic molecules

Thanks

Christian Heiliger Peter Zahn Bogdan Yavorsky Martin Gradhand Michael Czerner Martyna Pollock Wowa Maslyuk Peter Bose Igor Maznichenko Michael Fechner Steven Walczak Dima Fedorov

Vova Maslyuk

Organometallic benzene-vanadium wires

Kyoto January 23, 2009

• K. Miyajima, et al. Eur. Phys. J. D 34 177 (2005)

Kyoto January 23, 2009

ferromagnetic half-metallic

• W. Maslyuk et al. PRL 97, 097201(2006)
• 7
• 6
• 5
• 4
• 3
• 2
• 1

1 2 3 4

E1 E1 E2 E2 A1 A1 E1 E2 A1 EF

majority

Γ Δ Α Γ Δ Α

• 7
• 6
• 5
• 4
• 3
• 2
• 1

1 2 3 4

majority minority

A1

Energy (eV)

EF

Vanadium

Total DOS

DOS (arb.units)

E1 E1 E2 A1 A1 E2 E1 E2 EF

minority

• 3.0
• 2.5
• 2.0
• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5 2.0

Δ Γ

Energy, eV

A

LDA+U, U=3

Organometallic benzene-vanadium wires

Kyoto January 23, 2009

Charge density Spin density

• W. Maslyuk et al. PRL 97, 097201(2006)

Organometallic benzene-vanadium wires

Stretching

Kyoto January 23, 2009

Low spin - high spin transition

Kyoto January 23, 2009

Low spin - high spin transition

Kyoto January 23, 2009

Transport through the molecule

• 3.0
• 2.0
• 1.0

0.0 1.0 2.0 3.0

• 4.0
• 3.0
• 2.0
• 1.0

0.0 1.0 2.0 3.0 4.0

• 0.50
• 0.25

0.00 0.25 0.50

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5

Transmission Energy (eV)

VnBzn+1 n=1 n=2 n=3 n=4

EF

spin-up spin-down

4 . =

up down

G G

Transport through VnBzn+1 between Co(100) electrodes

Kyoto January 23, 2009

• 3.0
• 2.0
• 1.0

0.0 1.0 2.0 3.0

• 4.0
• 3.0
• 2.0
• 1.0

0.0 1.0 2.0 3.0 4.0

EF

• 0.50
• 0.25

0.00 0.25 0.50

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5

Transmission Energy (eV)

VnBzn+1 n=1 n=2 n=3 n=4 spin-down spin-up

5 . 1 =

up down

G G

Transport through VnBzn+1 between Co(100) electrodes

Kyoto January 23, 2009

• 3.0
• 2.0
• 1.0

0.0 1.0 2.0 3.0

• 4.0
• 3.0
• 2.0
• 1.0

0.0 1.0 2.0 3.0 4.0

EF

• 0.50
• 0.25

0.00 0.25 0.50

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5

Transmission Energy (eV)

VnBzn+1 n=1 n=2 n=3 n=4 spin-down spin-up

9 . 9 =

up down

G G

Transport through VnBzn+1 between Co(100) electrodes

Kyoto January 23, 2009

• 3.0
• 2.0
• 1.0

0.0 1.0 2.0 3.0

• 4.0
• 3.0
• 2.0
• 1.0

0.0 1.0 2.0 3.0 4.0

EF

• 0.50
• 0.25

0.00 0.25 0.50

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5

Transmission Energy (eV)

VnBzn+1 n=1 n=2 n=3 n=4 spin-down spin-up

1 . 10 =

up down

G G

Transport through VnBzn+1 between Co(100) electrodes

Kyoto January 23, 2009

0.5 0.4 0.3 0.2 0.1 0.0 1 2 3

• 3
• 2
• 1

1 2 3

Energy (eV) Bias (V)

Transmission

(spin-up)

0.5 0.4 0.3 0.2 0.1 0.0 1 2 3

• 3
• 2
• 1

1 2 3

Energy (eV) B i a s ( V )

Transmission

(spin-down)

Co(100)-V4Bz5-Co(100)

Bias dependence

Kyoto January 23, 2009

Summary

Kyoto January 23, 2009

• Tunneling current and TMR effect are

tailored by the interface between oxide barrier and first layer of the electrodes!

• Ferroelectricity changes at the surface!
• We predict magnetoelectric coupling via the

interface caused by charge transfer!

• Organometallic contacts show pronounced

spin-dependent transport

Collaborations and funding

Kyoto January 23, 2009

• A. Ernst, J. Henk, L. Sandratski,
• V. Stepanyuk, MPI Halle

P.H. Dederichs, R. Zeller, FZ Jülich

• F. Evers, A. Bagrets, FZ Karlsruhe
• W. Hergert, MLU Halle
• M. Scheffler, FHI Berlin
• P. Bruno, Grenoble
• M. Brandbyge, H. Skriver, TH Denmark
• J. Kudrnovsky, Prague
• P. M. Levy, New York University
• J. Staunton, University of Warwick
• M. Stiles, C. Heiliger, NIST Washington
• L. Szunyogh, TU Budapest
• W. Temmerman, Z. Szotek, Daresbury Laboratory
• P. Weinberger, TU Wien