  This paper introduces an oscillator scheme based on the oscillations of
magnetic domain walls due to spin-polarized currents, where the current is
injected perpendicular to the sample plane in a localized part of a nanowire.
Depending on the geometrical and physical characteristic of the system, we
identify two different dynamical regimes (auto-oscillations) when an
out-of-plane external field is applied. The first regime is characterized by
nucleation of domain walls (DWs) below the current injection site and the
propagation of those up to the end of the nanowire, we also found an
oscillation frequency larger than 5GHz with a linear dependence on the applied
current density. This simple system can be used as a tuneable steady-state
domain wall oscillator. In the second dynamical regime, we observe the
nucleation of two DWs which propagate back and forth in the nanowire with a
sub-GHz oscillation frequency. The micromagnetic spectral mapping technique
shows the spatial distribution of the output power is localized symmetrically
in the nanowire. We suggest that this configuration can be used as
micromagnetic transformer to decouple electrically two different circuits.
