Switching Boundary

1. Precessional reversal in orthogonal spin transfer magnetic random access memory devices H. Liu,1* D. Bedau,1 D. Backes,1 J. A. Katine,2 and A. D. Kent1,3 * : Presenter 1. Department of Physics, New York University, New York, New York 10003, USA 2. HGST Research, San Jose, California 95135, USA 3. Spin Transfer Technologies, 33 Arch Street, Boston, Massachusetts 02110, USA e easy axis mp electron m magnetization MOTIVATION EXPERIMENTAL TECHNIQUES DATA AND ANALYSIS[1], [2] • Switching Boundary • Pulse amplitude I of switching probability of 50% as a function of pulse duration τ over 10 order of magnitude in time. • For short pulse durations , the pulse amplitude required for switching increases dramatically. • For long pulses, the pulse amplitude depends weakly on pulse duration. DATA AND ANALYSIS SPIN–TRANSFER: the inverse of GMR effect • Switching probability (SP) distribution in all regimes • (a) dynamic regime: • (b) intermediate regime: SP distribution has a distinct form, neither the sigmoid form measured at short times nor the exponential form observed at long times. • (c) thermal regime: • Fitting results: • Spin torque – the amount of transverse angular momentum transferred in unit time. THEORETICAL MODELLING – short pulses • Landau-Lifshitz-Gilbert (LLG) equation + Spin Torque: • where • For all-perpendicular magnetization configuration: • If we assume that thermal fluctuation will NOT influence the process of switching since the duration of switching is short, then solving LLG equation: • τ is the pulse duration • θ0 is the initial magnetization angle • θτ is the final magnetization angle • The switching process is deterministic whereas the initial conditions are thermally distributed. • Universal switching probability distribution in the short time regime • SP only depends on the net angular momentum transferred from the current pulse. CONCLUSIONS • Switching probability distributions are measured for a broad range of pulse durations. • There are three distinct spin torque switching regimes. • Dynamic regime: angular momentum conservation. • Thermal regime: spin-transfer assisted thermal activation. • Intermediate regime: thermal fluctuations and spin-torque driven processes are both important–and cannot be separated. • The measured switching probability distributions at both short and long times are in good agreement with a single domain model that includes spin-transfer torques and thermal fluctuations . THEORETICAL MODELLING – long pulses • Thermal activation over an energy barrier, • which has been reduced by the pulse current. • where is the attempting time OUR PUBLICATIONS D. Bedau, H. Liu, J.-J. Bouzaglou, A. D. Kent, J. Z. Sun, J. A. Katine, E. E. Fullerton, and S. Mangin Appl. Phys. Lett. 96, 022514 (2010) D. Bedau, H. Liu, J. Z. Sun, J. A. Katine, E. E. Fullerton, S. Mangin, A. D. Kent arXiv: 1009.5240v1