  The point-like nature and exquisite magnetic field sensitivity of the
nitrogen vacancy (NV) center in diamond can provide information about the inner
workings of magnetic nanocircuits in complement with traditional transport
techniques. Here we use a single NV in bulk diamond to probe the stray field of
a ferromagnetic nanowire controlled by spin transfer (ST) torques. We first
report an unambiguous measurement of ST tuned, parametrically driven,
large-amplitude magnetic oscillations. At the same time, we demonstrate that
such magnetic oscillations alone can directly drive NV spin transitions,
providing a potential new means of control. Finally, we use the NV as a local
noise thermometer, observing strong ST damping of the stray field noise,
consistent with magnetic cooling from room temperature to $\sim$150 K.
