1. 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 I DC ≠ 0 -> Also agrees with a modified energy barrier dependent upon I DC Barrier height varies monotonically with applied dc current due to influence of spin-transfer torque 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 c0 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 ReversalField-Induced Reversal CDF *Presenting Author e-mail: daniel.gopman@physics.nyu.edu