Phase Coherent Precessional Magnetization Reversal in Micro-scopic Spin   Valve Elements
  We study the precessional switching of the magnetization in microscopic spin valve cells induced by ultra short in-plane hard axis magnetic field pulses. Stable and highly efficient switching is monitored following pulses as short as 140 ps with energies down to 15 pJ. Multiple application of identical pulses reversibly toggles the cell's magnetization be-tween the two easy directions. Variations of pulse duration and amplitude reveal alter-nating regimes of switching and non-switching corresponding to transitions from in-phase to out-of-phase excitations of the magnetic precession by the field pulse. In the low field limit damping becomes predominant and a relaxational reversal is found allowing switching by hard axis fields below the in-plane anisotropy field threshold. 
H.W. Schumacher, C. Chappert, P. Crozat, R.C. Sousa, P.P. Freitas, J.   Miltat, J. Fassbender and B. Hillebrands