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

1. 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