Magnetization reversal in the anisotropy-dominated regime using   time-dependent magnetic fields
  We study magnetization reversal using various r.f. magnetic pulses. We show numerically that switching is possible with simple sinusoidal pulses; however the optimum approach is to use a frequency-swept (chirped) r.f. magnetic pulse, the shape of which can be derived analytically. Switching times of the order of nanoseconds can be achieved with relatively small r.f. fields, independent of the anisotropy's strength. 
K. Rivkin and J. B. Ketterson