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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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slide1

Spin Electronics

Peng Xiong

Department of Physics and MARTECH

Florida State University

QuarkNet, June 28, 2002

slide2

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
slide3

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
slide4

Superparamagnetic Limit:

thermal stability of magnetic media

slide5

Semiconductor Random Access Memory: alternatives?

M

O

S

  • High speed
  • Low density
  • High power consumption
  • Volatile
slide6

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

slide7

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

slide8

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

slide9

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

slide10

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

slide11

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

slide12

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

slide13

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

slide14

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

slide15

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

slide16

~

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

slide17

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

slide18

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

slide19

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

slide20

Results: Zeeman splitting

+2.5T

-2.5T

T =400 mK

slide21

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

slide23

The People

Jeff Parker

Jazcek Braden

Steve Watts

Pavel Ivanov

Stephan von Molnár

Pedro Schlottmann

David Lind

slide24

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