Picosecond precessional magnetization reversal by magnetic field pulse shaping

We have developed a method to vary the shape of magnetic field pulses on a picosecond time scale and to monitor the magnetization response in all three dimensions by using time-resolved linear and nonlinear magneto-optical techniques. With this, we have measured the temporal response of rectangular 10×20 μm and elliptical 8×16 μm, 8 nm thin Permalloy (Ni₈₀Fe₂₀) elements due to in-plane magnetic field pulses with varying length and amplitudes. The data shows coherent precession of the magnetic spins in the elliptical elements, for large and small angle excitations. The shaping of the in-plane field pulses allows the control of the magnetization-motion on a picosecond timescale, so that stopping of the precessional motion of the underdamped magnetic system after one full precessional oscillation could be achieved. The large angle excitation showed a 160° switching of the magnetization within 300 ps. Further, it is demonstrated that the present technique can successfully be applied to improve the data integrity in magnetic random access memories (MRAMs).