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We can further study switching out of the P state as a function of dc current

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Thermally-Assisted Magnetization Reversal of a Nanomagnet with Spin-Transfer Torque. D. B. Gopman* 1 , D. Bedau, 1 S. Park 2 , D. Ravelosona 2 , E. E. Fullerton 3 , J. A. Katine 4 , S. Mangin 5 & A. D. Kent 1. 1 Department of Physics, New York University, New York, New York 10003, USA

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Thermally-Assisted Magnetization Reversal of a Nanomagnet with Spin-Transfer Torque

D. B. Gopman*1, D. Bedau,1 S. Park2, D. Ravelosona2, E. E. Fullerton3, J. A. Katine4, S. Mangin5 & A. D. Kent1

1Department of Physics, New York University, New York, New York 10003, USA

2Institut d’Electronique Fondamentale, UMR CNRS 8622, UPS, 91405 Orsay, France

3 CMRR, University of California, San Diego, La Jolla, California 92093-0401, USA

4 San Jose Research Center, Hitachi-GST, San Jose, California 95135, USA

5Institut Jean Lamour, UMR CNRS 7198, Nancy Université, UPV Metz, 54506 Vandoeuvre, France

*Presenting Author e-mail: [email protected]

MOTIVATION

SPIN-VALVE NANOPILLAR

STATISTICAL MEASUREMENTS, IDC ≠ 0

  • We can further study
  • switching out of the P state
  • as a function of dc current
  • Within our statistical accuracy (10,000 runs), data fits equilibrium model
  • Best-fit parameter E0 for each dataset allows us to determine barrier height dependence on dc current
  • Magnetization reversal in Co-Ni Spin-Valves
    • IDC=0 -> Agrees with equilibrium model
    • IDC ≠ 0 -> Also agrees with a modified energy barrier dependent upon IDC
  • Barrier height varies monotonically with applied dc current due to influence of spin-transfer torque

MOTIVATION

  • Nanoscale ferromagnets (FMs): Strong candidate for new devices based on spin transport—spintronic devices
  • Can reverse magnetization by applying a spin current
    • Switch high anisotropy FMs (U>40 kBT, T=300 K)
    • Low energy consumption
  • Applied dc spin currents also reduce the field required to reverse the magnetization
  • How does a dc spin current alter magnetization reversal?
  • SPIN VALVE: Nanostructured circuit with two series FM layers
  • GIANT MAGNETORESISTANCE (GMR)
    • Change in resistance with H
    • Easy Readout of Magnetization
    • RAP >> RP
  • SPIN-TRANSFER TORQUE
    • Transfers spin-angular momentum from
    • conduction electrons to magnetization
    • Destabilize/Switch Magnetization
  • Sweep H at fixed rate; measure Hswitch for each trial
    • Hswitch defined by sharp drop (rise) in GMR signal
  • Generate Switching histograms for ~ 10,000 magnetic field sweeps
    • Data is clearly NOT symmetrically distributed
  • Plot cumulative density on a Gaussian Quantile Scale for visual enhancement
  • Data (blue dots) fits equilibrium statistical model (red line) of thermal activation
  • Best-fit curve yields information about the energy barrier, E0, and the coercive field, Hc0
  • Two thin film FMs with perpendicular magnetic anisotropy
    • Both Co/Ni Superlattices
    • Reference layer magnetically “harder”
  • 300 nm x 50 nm lithographically patterned elliptical pillar
    • With extended electrodes for I-V measurements
  • Magnetoresistance ratio: (RAP-RP)/RP = 0.4 %

INTRODUCTION

STATIC I-V MEASUREMENTS

Current-Induced Reversal

Field-Induced Reversal

ENERGY BARRIER DEPENDENCE ON IDC

STATISTICAL MEASUREMENTS - IDC = 0

THEORY

  • Magnetization Dynamics
  • Neel-Brown Thermal Activation
  • Probability not to switch (H); IDC= 0
  • Can we continue to describe the switching field distributions in the presence of spin-transfer torque within this equilibrium model of thermal activation?

P->AP Switching

μ0Hc0= 175.4 mT

Γ0 = 1 GHz

v = 100 mT/s

E0 = 174.6 kBT

CDF

CONCLUSION

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