  We have measured the statistical properties of magnetic reversal in
nanomagnets driven by a spin-polarized current. Like reversal induced by a
magnetic field, spin-transfer-driven reversal near room temperature exhibits
the properties of thermally-activated escape over an effective barrier.
However, the spin-transfer effect produces qualitatively different behaviors
than an applied magnetic field. We discuss an effective current vs. field phase
diagram. If the current and field are tuned so that their effects oppose one
another, the magnet can be driven superparamagnetic.
