Thermally-Assisted Magnetization Reversal of a
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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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We can further study switching out of the p state as a function of dc current

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: daniel.gopman@physics.nyu.edu

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