Current perpendicular to plane CPP GMR

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Current perpendicular to plane (CPP) GMR
667 Spintronics Presentation
Weigang Wang 11/22/04
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Outline

• CPP V.S. CIP
• Model ( Valet Fert)
• Normal and Inversed CPP GMR
• CPP sample fabrication and control of magnetic
  states

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Why CPP?
Do not like in the CIP case, the current will not
be shunted by the Normal Metal layer, which is
not contribute to MR.
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Model ( Valet Fert) Main elements

• spin dependent scattering resulting in two
  current channels
• Series resistor
• Main Difference between CIP and CPP charge
  accumulation in CPP interfaces resulting in extra
  interface resistance.
• In most case, spin diffusion length (SDL) gtgt Mean
  free path ( MFP) SDL gtgt t ( layer thickness).
  SDL 1000A _at_ low T
• Definition of bulk and interface anisotropy ß and
  ?

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Model ( Valet Fert)Start from Boltzmann
equation, single domain FM layer, parabolic band
structure

Isolated Interface spin accumulation
significantly reduces the current asymmetry.
Interface resistance
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Model ( Valet Fert)
Bulk spin-dependent scattering
For P state, in FM and NM
AP
P
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Equivalent resistance array bulk scattering only
( analogy to traffic)
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Equivalent resistance arraywith both bulk
interface scattering
Symmetric or asymmetric ?
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All together ( M bilayers)
Agree well with experiment
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Determination of ß and ?
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Interface V.S. Bulk ß V.S. ?
Interface resistance dominates in usual
thicknesses (a few 10A) Bulk effect will take
over when thicknesses a few 100A
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Normal and Inversed CPP GMR
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CPP sample fabrication and control of magnetic
states

• Three ways for fabrication
• Sandwich between crossed S.C. stripes (good
  contact, but low T)
• Photo-lithography ( R-T, but contact R problem)
• nanowire
• To get P and AP state
• Different thickness of FM
• Exchange pinning

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References

• J. Bass, W.P. Pratt Jr. Physica B 321 (2002) 18
• S.F. Lee, et al., Phys. Rev. B 52 (1995) 15426.
• T. Valet, A. Fert, Phys. Rev. B 48 (1993) 7099.
• S.F. Lee, et al., J. Magn. Magn. Mater
• A. Fert, et al., Phys. Rev. B 52 (1995) 6513.