Coherent control of spin torque dynamics

We study time resolved precessional magnetization dynamics induced by spin momentum transfer in nanopillars of CoFeB/MgO/CoFeB magnetic tunnelling junctions (MTJ). Spin transfer torque precession of the CoFeB free layer is excited by ultra short current pulses (0.1 to 5 ns duration) with current densities around 106 A/cm2. The time resolved precession of the free layer is studied by measuring the time resolved magneto resistance change of the MTJ using a fast sampling oscilloscope. Our setup allows both to detect the spin torque precession during the current pulse and the magnetization ringing after pulse termination. From the decay of the precession we can derive the effective Gilbert damping parameter of the MTJ free layer. We show that by adapting the duration of the excitation pulse to integer multiples of the period of the spin torque precession the magnetization ringing can be coherently suppressed. Such coherent control of spin torque dynamics is a prerequisite for ultra fast ballistic spin transfer torque magnetization reversal