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POTENTIAL APPLICATIONS OF SPINTRONICS. M.Cahay. Dept. of ECECS, Univ.of Cincinnati, Cincinnati, Ohio 45221 http://www.ececs.uc.edu/~mcahay. February 4, 2005. Outline. A Little quBit of History Success Story: Giant Magnetoresistance Spin Valve

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potential applications of spintronics
POTENTIAL APPLICATIONS OF SPINTRONICS

M.Cahay

Dept. of ECECS, Univ.of Cincinnati,

Cincinnati, Ohio 45221

http://www.ececs.uc.edu/~mcahay

February 4, 2005

outline
Outline

A Little quBit of History

Success Story: Giant Magnetoresistance

Spin Valve

Requirements for spintronics

Zeeman, Spin-Orbit Effects

Injection, Manipulation, Detection

Magnetoresistive biosensors

Conclusions

brief history spintronics magnetoelectronics
Brief HistorySpintronics-Magnetoelectronics
  • Stern-Gerlach Experiment (Early 1920s)
  • spin concept – 1920s
  • Pauli-Dirac Equation (Late 1920s)
  • 1980s… : Study of Mesoscopic systems – Landauer-Buttiker Formalism
  • Breakdown of Moore’s Law?
  • 1988: Giant Magnetoresistance in Magnetic multilayers, magnetic read heads, magnetic sensors, spin valves.
brief history spintronics magnetoelectronics4
Brief HistorySpintronics-Magnetoelectronics
  • 1990: SPINFET proposal by Datta and Das
  • 1990s: Lots of work on Ferromagnet/ (metal, semiconductor, superconductor) interfaces.
  • DMS – diluted magnetic semiconductors (ZnMnSe, GaMnAs,GaMnN,…)
  • 1985: David Deutsch:

Quantum Mechanical Turing Machine

brief history spintronics magnetoelectronics5
Brief HistorySpintronics-Magnetoelectronics
  • 1995: P.Schor’s algorithm for fast factorization of large integers (cryptography)
  • 1997: L.K.Grover’s search algorithm for efficient search of large database
  • 1990s: Lots of proposal for implementation of qubits and quantum computers (NMR, Ion trap, quantum dot)
  • Search in Spintronics and Quantum Computing will continue to feed on each other
requirements for spintronic integrated circuits
Requirements for Spintronic Integrated Circuits
  • Simple device structure for high degree

of integration and high process yield.

  • Large magnetocurrent for high speed operation
  • High transconductance for high speed operation
  • High amplification capability (V, I, and/or power)
  • Small power delay product and small off-current

for low power dissipation

preliminaries stoner model
Preliminaries: Stoner Model

E(k)

Exchange Energy

k

Ferromagnetic Contact

contact selection
Contact Selection
  • Ferromagnetic contact (Fe, Ni, Co)
  • HMF candidates: Heusler Materials
  • Dilute Magnetic Semiconductors (GaMnAs, ZnMnSe, ZnMnTe,GaMnN…)
  • More recently, wide band gap ferromagnetic semiconductors and oxides

S.J. Pearson et al., “Wide band gap ferromagnetic Semiconductors and oxides”, Journal of Applied Physics, Vol.93, pp.1-13 (2003)

ferromagnetic contact semiconductor interfaces how good are they
Ferromagnetic contact/semiconductor interfacesHow good are they?

Why Ferromagnetic Contacts (Fe, Ni, Co)?

  • Because Curie Temperature Is Above Room Temperature!

Hence, devices could work at 300k.

  • FM are good source of spin polarized electron sources

(Stoner model)

Theoretical Predictions

  • Classical diffusion eq. predicts very small spin injection efficiency across Fe/Sm interface (G. Schmidt et al. PRB 62,R4790 (2000). Main reason: Large conductivity mismatch between the two materials.
  • Not so fast! E.I.Rashba (Phys.Rev.B 62 R16267 (2000)).

“If you can adjust interface resistance by using a tunneling barrier, the situation can improved drastically!”.

ferromagnetic contact semiconductor interfaces how good are they18
Ferromagnetic contact/semiconductor interfacesHow good are they?

Rashba's prediction was confirmed

experimentally using

(a) Schottky barriers

H.J.Zhu et al., PRL 87, 016601 (2001) (Fe/GaAs), 2% efficiency

A.T.Hanbicki et al, APL 80, 1240 (2002)

A.T.Hanbicki et al, APL 82, 4092 (2003), (Fe/AlGaAs), 33% efficiency

(b) Thin Metal Oxides

V.F. Motsynyi et al, APL 81, 265 (2002)

T. Manago and H. Akinaga, APL 81, 694 (2002)

(c) AlAs barriers

S.H.Chun et al, PRB 66, R100408 (2002).

spin relaxation mechanisms
Spin Relaxation Mechanisms

The Elliot-Yafet Scattering Mechanism

As a result of the SO-contribution to the crystal

Hamiltonian, conduction-band states of some

semiconductors are not spin eigenstates. This leads to

the possibility for spin-flip scattering even for spin

independent impurity scattering (due to Coulombic

scattering for instance).

For the same reason, spin-independent electron-electron

scattering can also cause spin-flip transitions

dyakonov perel spin relaxation in a quantum wire
DYAKONOV-PERELSPIN RELAXATION IN A QUANTUM WIRE

DRESSELHAUS HAMILTONIAN

RASHBA HAMILTONIAN

x

z

x

y

slide25

ONE REPULSIVE IMP. 300 angs from left contact

INFLUENCE OF SCATTERING STRENGTH

conclusions
Conclusions

Spintronics has already some success stories!

(giant magnetoresistance/spin valve)

Quantum Computing: Too early to tell!

Other potential: Spintronics & organics,

Spintronics & Biosensors, Magnetic Sensors.

Want to know more about it? Buy the book:

“Introduction to Spintronics”….in 2006.