Spin-Transfer Switching of Perpendicularly Magnetized Spin-valve Devices

1. Spin-Transfer Switching of Perpendicularly Magnetized Spin-valve Devices H. Liu1*, D. Bedau1, J-J. Bouzaglou1,3, A. D. Kent1, J. Z. Sun2, J. A. Katine4, E. E. Fullerton5 and S. Mangin3 * : Presenter 1Department of Physics, New York University, New York, NY 10003, USA 2IBM T. J. Watson Research Center, P.O. Box 218, Yorktown Heights, New York, 10598, USA 3LPM, Nancy-Université, UMR CNRS 7556, F-54506 VandoeuvreCedex, France 4San Jose Research Center, Hitachi-GST, San Jose, California 95135, USA 5CMRR, University of California, San Diego, La Jolla, California 92093-0401, USA Pulse (1 mA, 1 ns) 1 2 3 ? B = 0.2 T B = 0 T Apply measurement field and current Saturate Check if switched Apply pulse If switched go here If NOT switched go here 4 Pulse 100 times and we have :switching probability = # of switched / 100 for AP to P at 0 T, 1 mA, 1 ns INTRODUCTION • Background • Giant Magneto-Resistance: • R Anti-Parallel > R parallel Sample • Spin-valve nanopillars with perpendicularly magnetized free and reference layers. EXPERIMENTS AND ANALYSIS EXPERIMENT TYPE 2: SWITCHING PROBABILITY ~ I OR T EXPERIMENT TYPE 1: PHASE DIAGRAM Use the same process as Experiment Type 1 to get a switching probability of one pulse duration and amplitude pair. Fix the pulse duration(amplitude), apply different amplitudes (durations) and get the switching probability. SWITHCHING PROBABILITY ~ T AT FIXED CURRENT • For short time pulse, if we ignore the thermal effects during the process of switching, the results of pulsing is totally determined by the initial condition (angle) of the spin. Therefore, to get a probability distribution, we can assume the initial angle of the spin has a Boltzmann distribution since the sample sits in room temperature for several hundreds of milliseconds (as the lock – in amplifier’s time constant) before each pulse. SWITHCHING PROBABILITY ~ I AT FIXED DURATION THEORITICAL MODELLING • Landau-Lifshitz-Gilbert (LLG) equation + Spin Torque: • where • This spin torque term can be interpreted as the electrons of the current have a certain probability of exchanging their spins with the lattice of the FM layer. • Short time: I > Ic0 • If we assume the thermal fluctuation will NOT play any important role in the process of switching, then we have: • And : • where: • Long time: I < Ic0 • We assume that the magnetization escapes from a potential well due to thermal fluctuation and the current only reduces the potential barrier. SHORT TIME PULSE We can assume that all spin current above a critical current would donate its spins to the free layer by some efficiency, which will cause the reversal of the layer’s magnetization. Therefore, we will have: which will be the same as the linearized the switching time result from LLG equation. CONCLUSIONS THREE DIFFERENT REGION. SHORT TIME: THERMAL EFFECTS MAY ONLY CHANGE INITIAL STATES BUT NOT DURING PROCESS. LONG TIME: THERMALLY ASSISTED ESCAPTING A POTENTIAL WELL REFERENCE J. Z. Sun, Proceedings of SPIE vol.5359, 445 (2004) J. Z. Sun, Physics Review B Volume 62, Number 1 (2000)