  The advantage of an ultra-fast frequency-tunability of spin-torque
nano-oscillators (STNOs) that have large (> 100MHz) relaxation frequency of
amplitude fluctuations is exploited to realize ultra-fast wide-band
time-resolved spectral analysis at nanosecond time scale with the frequency
resolution limited only by the 'bandwidth' theorem. The demonstration is
performed with an STNO generating in the 9 GHz frequency range, and comprised
of a perpendicular polarizer and a perpendicularly and uniformly magnetized
'free' layer. It is shown that such a uniform-state STNO-based spectrum
analyzer can efficiently perform spectral analysis of frequency-agile signals
with rapidly varying frequency components.
