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Magnetic Tweezers for the Measurement of Twist and Torque
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Fluctuation theorem for a small engine and magnetization switching by spin torque.

Yasuhiro Utsumi1, Tomohiro Taniguchi2

  • 1Department of Physics Engineering, Faculty of Engineering, Mie University, Tsu, Mie, 514-8507, Japan.

Physical Review Letters
|May 23, 2015
PubMed
Summary

We investigated nanomagnet switching using fluctuating spin torque from electron spin currents. A threshold voltage was identified, above which switching occurs and below which it is blocked, consistent with fluctuation theorems for small engines.

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Area of Science:

  • Condensed Matter Physics
  • Quantum Mechanics
  • Nanotechnology

Background:

  • Nanomagnet switching is crucial for data storage.
  • Spin torque is a key mechanism for manipulating nanomagnets.
  • Fluctuations in spin torque are not fully explained by the fluctuation-dissipation theorem.

Purpose of the Study:

  • To analyze nanomagnet reversal using fluctuating spin torque.
  • To investigate the role of nonequilibrium electron spin currents.
  • To explore the applicability of fluctuation theorems to small engines.

Main Methods:

  • Estimating joint probability distributions of work and heat.
  • Applying the theory of full-counting statistics.
  • Accounting for the backaction effect of spin angular momentum pumping.

Main Results:

  • Predicted a threshold voltage for probabilistic switching events.
  • Demonstrated that spin-torque shot noise induces switching.
  • Showed that events are blocked below the threshold voltage.

Conclusions:

  • Fluctuating spin torque can induce nanomagnet reversal.
  • The fluctuation theorem is satisfied for this small engine system.
  • Full-counting statistics and backaction are essential for theoretical consistency.