Picosecond coherent magnetisation reversal by magnetic field pulse shaping

Summary form only given. The understanding of coherent switching of a magnetic thin film system is required for practical applications such as the future MRAM memory cell. The Landau-Lifshitz dynamics describing the precessional motion of the magnetic spin system is studied by excitation of lithographically structured micron-sized Permalloy elements by ultra-short magnetic field pulses. The shortest time needed for the reversal of the magnetisation is given by the half of one full precessional oscillation but for this a complete suppression of the magnetisation ringing after the switching process is needed. This requires stopping of the precessional motion at exactly this time, which in practice means stopping this motion on a time scale much shorter than the typical damping time. We will present a technique that enables us to arbitrarily control the magnetisation precession on a picosecond timescale. The method is based on two independently triggered GaAs photoswitches, excited by femtosecond laserpulses. The femtosecond-laserpulse-system allows us to measure the in-plane components of the magnetisation by means of magnetisation induced second harmonic generation (MSHG) while the polar component is probed by linear MOKE.