•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 E 0 for each dataset allows us to determine barrier height dependence on dc current •Magnetization reversal in Co-Ni Spin- Valves • I DC =0 -> Agrees with equilibrium model • Sweep H at fixed rate; measure H switch for each trial • H switch 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, E 0 , and the coercive field, H 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 2 Institut 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 5 Institut Jean Lamour, UMR CNRS 7198, Nancy Université, UPV Metz, 54506 Vandoeuvre, France 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 k B T, 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 • R AP >> R P •SPIN-TRANSFER TORQUE • Transfers spin-angular momentum from conduction electrons to magnetization • Destabilize/Switch Magnetization INTRODUCTION THEORY •Magnetization Dynamics •Neel-Brown Thermal Activation • Probability not to switch (H); I DC = 0 •Can we continue to describe the switching field distributions in the presence of spin-transfer torque within this equilibrium model of thermal activation? MOTIVATION SPIN-VALVE NANOPILLAR •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: (R AP -R P )/R P = 0.4 % STATIC I-V MEASUREMENTS STATISTICAL MEASUREMENTS, I DC ≠ 0 STATISTICAL MEASUREMENTS - I DC = 0 CONCLUSION P->AP Switching μ 0 H c0 = 175.4 mT Γ 0 = 1 GHz v = 100 mT/s E 0 = 174.6 k B T ENERGY BARRIER DEPENDENCE ON I DC Current-Induced Reversal Field-Induced Reversal CDF *Presenting Author e-mail: [email protected]

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

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•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

•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

Thermally-Assisted Magnetization Reversal of a Nanomagnet with Spin-Transfer TorqueD. B. Gopman*1, D. Bedau,1 S. Park2, D. Ravelosona2, E. E. Fullerton3, J. A. Katine4, S. Mangin5 & A.

D. Kent11Department of Physics, New York University, New York, New York 10003, USA

2Institut d’Electronique Fondamentale, UMR CNRS 8622, UPS, 91405 Orsay, France3 CMRR, University of California, San Diego, La Jolla, California 92093-0401, USA

4 San Jose Research Center, Hitachi-GST, San Jose, California 95135, USA5Institut Jean Lamour, UMR CNRS 7198, Nancy Université, UPV Metz, 54506 Vandoeuvre, France

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

INTRODUCTION

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?

MOTIVATION SPIN-VALVE NANOPILLAR

•Two thin film FMs with perpendicular magnetic anisotropy•Both Co/Ni Superlattices•Reference layer magnetically “harder”

•300 nm x 50 nm lithographically patterned elliptical pillarWith extended electrodes for I-V measurements

•Magnetoresistance ratio: (RAP-RP)/RP = 0.4 %

STATIC I-V MEASUREMENTS

STATISTICAL MEASUREMENTS, IDC ≠ 0

STATISTICAL MEASUREMENTS - IDC = 0

CONCLUSION

P->AP Switchingμ0Hc0 = 175.4 mT

Γ0 = 1 GHzv = 100 mT/s

E0 = 174.6 kBT

ENERGY BARRIER DEPENDENCE ON IDC