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Spin Pumping and Torque Statistics in the Quantum Noise Limit.

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This study introduces a new Keldysh action to analyze charge, energy, and spin torque fluctuations in metallic nanomagnets. The method is valid for all temperature ratios, offering insights into spintronic devices.

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Area of Science:

  • Condensed matter physics
  • Spintronics
  • Quantum mechanics

Background:

  • Understanding stochastic charge, energy, and spin torque is crucial for spintronic device applications.
  • Existing models often have limitations regarding temperature dependence and quantum effects.

Purpose of the Study:

  • To derive a general Keldysh action for stochastic currents in a metallic nanomagnet coupled to a magnetic metal.
  • To analyze spin torque phenomena beyond the limitations of previous approaches, particularly concerning temperature ratios.
  • To explore quantum corrections in spintronic fluctuation relations and noise.

Main Methods:

  • Derivation of a Keldysh action for the tunnel barrier.
  • Analysis of stochastic currents in a precessing magnetization system.
  • Application of the action to derive spintronic fluctuation relations and pumped current noise.

Main Results:

  • A novel Keldysh action is derived, valid for arbitrary ratios of ℏΩ/k_{B}T.
  • Spintronic fluctuation relations and the quantum limit of pumped current noise are obtained.
  • Fluctuations are analyzed for stable magnetization precession and torque-induced switching.

Conclusions:

  • The derived Keldysh action provides a versatile tool for studying spintronic fluctuations.
  • Quantum corrections become significant when the precession rate exceeds temperature (ℏΩ≳k_{B}T).
  • This work advances the theoretical understanding of spin torque and current noise in magnetic nanostructures.