  We investigate the dynamics of an injection locked in-plane uniform spin
torque oscillator for several forcing configurations at large driving
amplitudes. For the analysis, the spin wave amplitude equation is used to
reduce the dynamics to a general oscillator equation in which the forcing is a
complex valued function $F(p,{\psi})\propto{\epsilon}_1
(p)cos({\psi})+i{\epsilon}_2 (p)sin({\psi})$. Assuming that the oscillator is
strongly nonisochronous and/or forced by a power forcing
$(|{\nu}{\epsilon}_1/{\epsilon}_2 |\gg 1)$, we show that the parameters
${\epsilon}_{1,2} (p)$ govern the main bifurcation features of the Arnold
tongue diagram : (i) the locking range asymmetry is mainly controlled by
$d{\epsilon}_1 (p)/dp$, (ii) the Taken-Bogdanov bifurcation occurs for a power
threshold depending on ${\epsilon}_{1,2} (p)$ and (iii) the frequency
hysteretic range is related to the transient regime through the resonant
frequency at zero mismatch frequency. Then, the model is compared with the
macrospin simulation for driving amplitudes as large as $10^0-10^3 A/m$ for the
magnetic field and $10^{10}-10^{12} A/m^2$ for the current density. As
predicted by the model, the forcing configuration (nature of the driving
signal, applied direction, the harmonic orders) affects substantially the
oscillator dynamic. However, some discrepancies are observed. In particular,
the prediction of the frequency and power locking range boundaries may be
misestimated if the hysteretic boundaries are of same magnitude order.
Moreover, the misestimation can be of two different types according if the
bifurcation is Saddle node or Taken Bogdanov. These effects are a further
manifestation of the complexity of the dynamics in nonisochronous
auto-oscillators.
