Spin Electronics

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Spin Electronics
Peng Xiong
Department of Physics and MARTECH Florida State
University
QuarkNet, June 28, 2002
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Moores 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

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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

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Superparamagnetic Limit thermal stability of
magnetic media
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Semiconductor Random Access Memory alternatives?
M
O
S

• High speed
• Low density
• High power consumption
• Volatile

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Metal-based Spintronics Spin valve and magnetic
tunnel junction
Applications magnetic sensors, MRAM, NV-logic
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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
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Spin Injection the conductivity mismatch
I
Schmidt et.al., PRB, 2000
I
RN
RF
I
SC
mF
RN
RF
mN
mF
mN
FM
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Measurement of spin polarization using a
superconductor
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Andreev reflection normal metal/superconductor
E
S
N
D
eV
EF
-D
N(E)
N
S
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Andreev reflection normal metal/superconductor
p 0
Z 0 clean metallic contact
Z gtgt 1 tunnel junction
Z 1 in-between
Blonder, Tinkham, and Klapwijk, PRB, 1982
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Andreev reflection ferromagnet/superconductor
p 75
E
F
S
Z 0 metallic contact
D
eV
EF
-D
Z 1 in-between
DOS
Z gtgt 1 tunnel junction
V
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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 gtgt 1 tunnel junction
Z gtgt 1 tunnel junction
V
V
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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
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CrO2 Film Growth Chemical Vapor Deposition
Furnace, T280 C
O2 flow
Heater block, T400C
substrate
Cr8O21 precursor
Ivanov, Watts, and Lind, JAP, 2001
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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
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Results CrO2/(I)/Pb junctions
Metallic contact Z 0 p 97

• T 1.2 K
• 1.44 meV

Tunnel junction
T 400 mK
High quality barrier w/o inelastic scattering
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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
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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
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Results Zeeman splitting
2.5T
-2.5T
T 400 mK
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• 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

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CrO2/I/Co magnetic tunnel junction
H
Co
CrO2
AlOx
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The People
Jeff Parker Jazcek Braden Steve Watts Pavel Ivanov
Stephan von Molnár Pedro Schlottmann David Lind
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Lets 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 Theres Plenty of Room at
the Bottom 1959 APS Meeting