POTENTIAL%20APPLICATIONS%20OF%20SPINTRONICS

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POTENTIAL APPLICATIONS OF SPINTRONICS
M.Cahay
February 4, 2005

• Dept. of ECECS, Univ.of Cincinnati,
• Cincinnati, Ohio 45221
• http//www.ececs.uc.edu/mcahay

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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

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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 Moores Law?
• 1988 Giant Magnetoresistance in Magnetic
  multilayers, magnetic read heads, magnetic
  sensors, spin valves.

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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

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Brief HistorySpintronics-Magnetoelectronics

• 1995 P.Schors algorithm for fast factorization
  of large integers (cryptography)
• 1997 L.K.Grovers 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

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SIA ROADMAP - Moores Law
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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

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Preliminaries Stoner Model
E(k)
Exchange Energy
k
Ferromagnetic Contact
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GMR Read Head
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RAM with GMR Elements
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Preliminiaries Zeeman Effect
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PreliminariesSpin-Orbit Interaction
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Ferromagnet/Sm Interface
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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)

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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!.

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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).

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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

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DYAKONOV-PERELSPIN RELAXATION IN A QUANTUM WIRE

• DRESSELHAUS HAMILTONIAN
• RASHBA HAMILTONIAN

x
z
x
y
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RAMSAUER (FABRY-PERROT) RESONANCES
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ONE REPULSIVE IMP. 300 angs from left
contact INFLUENCE OF SCATTERING STRENGTH
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Magnetoresistive-Based BiosensorsD.L.Graham et
al, Trends in biotechnology vol.22, 455 (2004)
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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.