Spin Electronics
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Spin Electronics. Peng Xiong. Department of Physics and MARTECH Florida State University. QuarkNet, June 28, 2002. SOURCE. GATE. DRAIN. MOSFET. Moore’s Law… is the end in sight?. Speed: 10 0 Hz Size: 10 -2 m Cost: $10 6 /transistor. Speed: 10 9 Hz Size: 10 -7 m

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Spin electronics

Spin Electronics

Peng Xiong

Department of Physics and MARTECH

Florida State University

QuarkNet, June 28, 2002


Spin electronics

SOURCE

GATE

DRAIN

MOSFET

Moore’s Law… is the end in sight?

Speed: 100 Hz

Size: 10-2 m

Cost: $106/transistor

  • Speed: 109 Hz

  • Size: 10-7 m

  • Cost: $10-5/transistor


Spin electronics

Magnetic Information Storage: superparamagnetic limit

  • Density: 20 Gb/in2

  • Speed: 200 Mb/s

  • Size: f2.5” x 2

  • Capacity: 50 Gb

  • Density: 2 kb/in2

  • Speed: 70 kb/s

  • Size: f24” x 50

  • Capacity: 5 Mb


Spin electronics

Superparamagnetic Limit:

thermal stability of magnetic media


Spin electronics

Semiconductor Random Access Memory: alternatives?

M

O

S

  • High speed

  • Low density

  • High power consumption

  • Volatile


Spin electronics

H

R

H

E

E

E

E

H

M

EF

EF

N(E)

N(E)

Metal-based Spintronics:

Spin valve and magnetic tunnel junction

Applications: magnetic sensors, MRAM, NV-logic


Spin electronics

GATE

Spintronics in Semiconductor: spin transistor

  • Dreams

  • High performance

  • opto-electronics

  • Single-chip computer

  • (instant on; low power)

  • Quantum computation

Datta and Das, APL, 1990

H

SOURCE

DRAIN

GaAs

  • Issues

  • Spin polarized material

  • Spin injection

  • Spin coherence

  • Spin detection

H


Spin electronics

  • Solutions:

  • Use injector with 100%

  • spin polarization

  • Non-diffusive injection

  • Conductivity matching

Spin Injection: the conductivity mismatch

I

Schmidt et.al., PRB, 2000

RN­

RF­

SC

mF­

RN¯

RF¯

mN­

mF¯

mN¯

FM


Spin electronics

E

E

CrO2: a half metal

Tc = 400 K

m = 2mB/Cr

p = 100%

Uex

E

4s

Schwarz, J. Phys. F, 1986

normal metal

half-metallic

ferromagnet

3d

metallic ferromagnet

Measurement of spin polarization: using a superconductor


Spin electronics

  • Question:

  • What could happen to an electron with energy eV < D when it hits S from N?

  • bounce back;

  • go into S as an electron;

  • C. go into S in a Cooper pair.

  • A and B

  • B and C

  • C and A

  • A and B and C

Andreev reflection: normal metal/superconductor

E

S

N

D

eV

EF

-D

N(E)

N

S


Spin electronics

Andreev reflection: normal metal/superconductor

p = 0

Z = 0

clean metallic contact

Z ~ 1

in-between

Z >> 1

tunnel junction

Blonder, Tinkham, and Klapwijk, PRB, 1982


Spin electronics

Andreev reflection: ferromagnet/superconductor

p = 75%

E

F

S

Z = 0

metallic contact

D

eV

EF

-D

Z ~ 1

in-between

DOS

Z >> 1

tunnel junction

V


Spin electronics

Comparison: normal metal and ferromagnet

p = 75%

p = 0

Z = 0

metallic contact

Z = 0

metallic contact

Z ~ 1

in-between

Z ~ 1

in-between

Z >> 1

tunnel junction

Z >> 1

tunnel junction

V

V


Spin electronics

Spin Polarization of CrO2: our approach

Planar junction  real device structure

Artificial barrier  controlled interface

Preservation of spin polarization

at and across barrier

Key step: controlled surface modification

of CrO2 via Br etch


Spin electronics

CrO2 Film Growth: Chemical Vapor Deposition

Furnace, T=280° C

O2 flow

Heater block, T=400°C

substrate

Cr8O21 precursor

Ivanov, Watts, and Lind, JAP, 2001


Spin electronics

~

V

Lock-in

dV/dI vs V in He4 (1K) or He3 (0.3K) cryostats

Junction Fabrication and Measurement

  • Grow CrO2 film

  • Pattern CrO2 stripe

  • Surface modification: Br etch

  • Deposit S cross stripes

Pb or Al

Pb or Al

I

CrO2

CrO2

TiO2


Spin electronics

Results: CrO2/(I)/Pb junctions

Metallic contact

Z = 0p = 97%

T = 1.2 K

  • = 1.44 meV

Tunnel junction

T = 400 mK

High quality barrier

w/o inelastic scattering


Spin electronics

mH

H

Measurement of spin polarization in high-Z junctions:

using Zeeman splitting

E

D

eV

EF

-D

eV/D

N(E)

Meservey and Tedrow,

Phys. Rep., 1994

S

F


Spin electronics

Zeeman splitting in an F/I/S junction

CrO2

In order to get high Hc:

Ultrathin S film

Parallel field

Negligible s-o interaction

H

Al

Al

CrO2


Spin electronics

Results: Zeeman splitting

+2.5T

-2.5T

T =400 mK


Spin electronics

Summary (CrO2)

Verified half-metallicity of CrO2

Engineered an artificial barrier on CrO2 surface

Preserved complete spin polarization at interface

Achieved full spin injection from a half metal

Future

Apply the technique to other systems

Magnetic tunnel junction


Spin electronics

CrO2/I/Co magnetic “tunnel” junction

H

Co

CrO2

AlOx


Spin electronics

The People

Jeff Parker

Jazcek Braden

Steve Watts

Pavel Ivanov

Stephan von Molnár

Pedro Schlottmann

David Lind


Spin electronics

Let’s build

“computers with wires no wider than 100 atoms, a microscope that could view individual atoms, machines that could manipulate atoms 1 by 1, and circuits involving quantized energy levels or the interactions of quantized spins.”

Richard Feynman –

“There’s Plenty of Room at the Bottom”

1959 APS Meeting


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