•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]