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spin. charge. 10 nm. Pure Spin Currents via Non-Local Injection and Spin Pumping. Axel Hoffmann Materials Science Division and Center for Nanoscale Materials Argonne National Laboratory. Thanks to.

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pure spin currents via non local injection and spin pumping

spin

charge

10 nm

Pure Spin Currentsvia Non-Local Injectionand Spin Pumping

Axel Hoffmann

Materials Science Division and Center for Nanoscale MaterialsArgonne National Laboratory

thanks to
Thanks to

Goran Mihajlović, Oleksandr Mosendz, Yi Ji, John E. Pearson, Frank Y. Fradin, J. Sam Jiang, and Sam D. Bader

Materials Science Division and Center for Nanoscale MaterialsArgonne National Laboratory

Miguel A. Garcia

Departamento Física de Materiales, Universidad Complutense de Madrid

Gerrit E. W. Bauer

Kavli Institute of NanoScience, Delft University of Technology

Peter Fischer and Mi-Young Im

Center for X-ray Optics, Lawrence Berkeley National Laboratory

$$$ Financial Support $$$DOE-BES

outline

I

V

1 m

spin

charge

10 nm

Outline
  • Why Pure Spin Currents?
  • Electrical Injection
  • Spin Hall Effect
  • Spin Pumping
  • Conclusions
spintronics

New Physics

Nobel Prize

Novel Devices

Spintronics

Putting

into Electronics

charge vs spin currents

Moving Spins

Spin Dynamics

Charge vs. Spin Currents

Charge

Spin

No Need for Moving Spin: Potential for Low Power Dissipation!

J. Shi, et al., Phys. Rev. Lett. 96, 076604 (2006).

new goal
New Goal:

Take the

Charge out of

Spintronics!

can we generate pure spin currents in paramagnetic materials
Can we generate pure spin-currentsin paramagnetic materials?

YES !!!

  • Non-local geometries
  • Spin-dependent scattering (Spin-Hall)
  • Spin pumping
pure spin currents the johnson transistor

V

e-

or

First Experimental Demonstrations

I+

I-

V

Bulk Al: s = 450 m (4.2 K)

0

Collector

Cu film: s = 1 m (4.2 K)

M. Johnson and R. H. Silsbee,Phys. Rev. Lett. 55, 1790 (1985)

Jedema et al., Nature 410, 345 (2001)

Pure Spin Currents: The Johnson Transistor

N

M. Johnson and R. H. Silsbee,Phys. Rev. Lett. 55, 1790 (1985)

M. Johnson,Science 260, 320 (1993)

L

F1

F2

F2

F2

F2

F1

N

Emitter

Base

lateral spin valve with gold

s = 63  15 nm

In gold at 10 K

Lateral Spin-Valve with Gold

a.c. current source

Lock-in detection

Y. Ji, et al., Appl. Phys. Lett. 85, 6218 (2004)

lateral spin valve with copper
Lateral Spin-Valve with Copper

Shadow Evaporation

SEM Image

Finished Device

500 nm

Y. Ji, et al.,Appl. Phys. Lett. 88, 052509 (2006)

spin diffusion length in copper
Spin Diffusion Length in Copper

P= 7%

T = 10 K

Y. Ji, et al.,Appl. Phys. Lett. 88, 052509 (2006)

spin signal at room temperature
Spin-Signal at Room Temperature

Co/Cu Lateral Spin-Valve

L = 300 nm, T = 10 K

L = 350 nm, T = 300 K

s ≈ 110 nmat room temperature

spin hall effect
Spin Hall Effect

Spin-dependent scattering gives rise to transverse spin imbalance

of charge currents

J. E. Hirsch, Phys. Rev. Lett. 83, 1834 (1999)

M. I. Dyakonov and V. I. Perel, JETP Lett. 13, 467 (1971)

Direct observation in GaAs

with optical detection

Y. K. Kato et al., Science 306, 1910 (2004)

spin skew scattering

-

-

-

-

Spin-Skew Scattering

B

E

+

nucleus

electron

spin hall vs inverse spin hall
Spin Hall vs. Inverse Spin Hall

Spin Hall

Charge Current

Transverse

Spin Imbalance

Inverse Spin Hall

Spin Current

Transverse

Charge Imbalance

Spin Dependent Scattering

spin hall angle

spin Hall conductivity

charge conductivity

stronger spin orbit interaction larger

Importance:

  • understanding the effect of SO coupling on electron transport
  • recognizing materials for spintronics applications

Goal:

  • experiments to quantify
Spin Hall Angle
quantifying spin hall angle in metals
Quantifying Spin Hall Angle in Metals

Ferromagnetic resonance:

Magnetotransport measurements:

T. Kimura et al.,

PRL98, 156601 (2007)

E. Saitoh et al.,

APL88, 182509 (2006)

Pt:

= 0.0037

S. O. Valenzuela & M. Tinkham,

Nature442, 176 (2006)

K. Ando et al.,

PRL101, 036601 (2008)

Al:

= 0.0001- 0.0003

Pt:

= 0.08

T. Seki et al.,

Nature Mater. 7, 125 (2008)

Au:

= 0.113

  • Large discrepancies in  values !
  • Ferromagnets always used to generate/detect spin currents
  • need to know spin polarization efficiency at injector/detector

possible spurious signals: Hall, Anomalous Hall, MR

How about Spin Hall effects without ferromagnets!

charge current teleportation

Direct Spin Hall Effect

Generate Pure Spin Current

Inverse Spin Hall Effect

Detect Pure Spin Current

Charge Current Teleportation

E. M. Hankiewicz et al., Phys. Rev. B 70, 241301(R) (2004)

J.E. Hirsch, Phys. Rev. Lett.83, 1834 (1999)

D. A. Abanin et al., Phys. Rev. B 79, 035304 (2009)

M. I. Dyakonov, Phys. Rev. Lett.99, 126601 (2007)

Theoretical Idea: Use Spin Hall Effects Twice!

L

gold hall bar structures

w = 110 nm t = 60 nm

1 µm

Gold Hall Bar Structures

Spin Hall Angle in Gold: < 0.02

Too small to be practically useful!

5 μm

Mihajlović et al., Phys. Rev. Lett. 103, 166601 (2009)

unusual application of spin dynamics
Unusual Application of Spin Dynamics

As found in: Queen Victoria Pub, Durham, U. K.

spin pumping

F

N

IS

Spin Pumping
  • Ferromagnetic Resonance results in time-dependent interfacial spin accumulation
  • This spin accumulation diffuses away from the interface
  • Results in net dc spin current perpendicular to interface
  • Additional spin current gives rise to additional damping
  • Quantify spin current from linewidth broadening
combine spin pumping and inverse hall effect
Combine Spin Pumping and Inverse Hall Effect
  • Use Spin Pumping to Generate Pure Spin Current
  • Quantify Spin Current from FMR
  • Measured Voltage Directly Determines Spin Hall Conductivity
  • Key Advantage: Signal Scales with Device Dimension
determine spin hall angle for many materials
Determine Spin Hall Angle for Many Materials

Pt

Au

Mo

  • = 0.0120±0.0001
  • = 0.0025±0.0006
  • = -0.00096±0.00007

Technique easily adapted to any material!

can we image spin accumulation directly
Can we Image Spin Accumulation Directly?

How about X-ray Dichroism?

Image at Cu L-edge

Magnetic Difference Images

Mosendz et al., Phys. Rev. B 80, 104439 (2009)

is there any hope for x rays
Is There Any Hope for X-Rays?

Ferromagnet

(i.e., typical TM)

Spin Accumulation

E

E

d

d

s

s

N(E)

N(E)

Contrast due to different density of states at Fermi-level

Contrast due to spin-splitting?

Well below 1 meV!

conclusions

I

V

1 m

spin

charge

10 nm

Conclusions
  • Spin Currents behave differentcompared to Charge Currents
    • Possibility of Reduced Power Dissipation
  • Non-Local Electrical Injection
    • Generate Pure Spin Currents
    • Study Spin Relaxation
  • Spin Hall Effects
    • Generate and Detect Spin Currentsw/o Ferromagnets
  • Spin Pumping
    • Generate Spin Currentsw/o Electric Charge Currents