  The effects of a weak microwave field in the magnetization dynamics driven by
spin-transfer-torque in spin-valves with perpendicular materials have been
systematically studied by means of full micromagnetic simulations. In the
system we studied, depending on the working point (bias field and current) in
the dynamical stability diagram, we observe either resonant switching and
injection locking. The resonant switching, observed in the switching region,
occurs when the field frequency is approaching the frequency of the main
pre-switching mode giving rise to an asymmetric power distribution of that mode
in the sectional area of the free layer. At the resonant frequency, the
switching time is weakly dependent on the relative phase between the instant
when the current pulse is applied and the microwave field. The injection
locking, observed in the dynamical region, is characterized by the following
properties: (i) a locking bandwidth which is linearly dependent on the force
locking, and (ii) a locking for integer harmonics of the self-oscillation
frequency. We compare our numerical results with analytical theory for
non-autonomous non-linear system obtaining a good agreement in the current
region where the oscillation frequency and output power are characterized from
a linear relationship.
