  We investigate the magnetization reversal of single-domain magnetic
nanoparticle driven by linear down-chirp microwave magnetic field pulse.
Numerical simulations based on the Landau-Lifshitz-Gilbert equation reveal that
solely down-chirp pulse is capable of inducing subnanosecond magnetization
reversal. With a certain range of initial frequency and chirp rate, the
required field amplitude is much smaller than that of constant-frequency
microwave field. The fast reversal is because the down-chirp microwave field
acts as an energy source and sink for the magnetic particle before and after
crossing over the energy barrier, respectively. Applying a spin-polarized
current additively to the system further reduces the microwave field amplitude.
Our findings provide a new way to realize low-cost and fast magnetization
reversal.
