  In this paper, a 3-terminal spin-transfer torque nano-oscillator (STNO) is
studied using the concurrent spin injection of a spin-polarized tunneling
current and a spin Hall current exciting the free layer into dynamic regimes
beyond what is achieved by each individual mechanism. The pure spin injection
is capable of inducing oscillations in the absence of charge currents
effectively reducing the critical tunneling current to zero. This reduction of
the critical charge currents can improve the endurance of both STNOs and
non-volatile magnetic memories (MRAM) devices. It is shown that the system
response can be described in terms of an injected spin current density $J_s$
which results from the contribution of both spin injection mechanisms, with the
tunneling current polarization $p$ and the spin Hall angle $\theta$ acting as
key parameters determining the efficiency of each injection mechanism. The
experimental data exhibits an excellent agreement with this model which can be
used to quantitatively predict the critical points ($J_s = -2.26\pm 0.09 \times
10^9 \hbar/e$ A/m$^2$) and the oscillation amplitude as a function of the input
currents. In addition, the fitting of the data also allows an independent
confirmation of the values estimated for the spin Hall angle and tunneling
current polarization as well as the extraction of the damping $\alpha = 0.01$
and non-linear damping $Q = 3.8\pm 0.3$ parameters.
