  We have measured the relaxation time of a thermally unstable ferromagnetic
nanoparticle incorporated into a magnetic tunnel junction (MTJ) as a function
of applied magnetic field, voltage V (-0.38 V < V < +0.26 V), and temperatures
(283 K< T< 363 K) . By analyzing the results within the framework of a modified
N\'eel-Brown formalism we determine the effective attempt time of the
nanoparticle and also the bias dependences of the in-plane and out-of-plane
spin torques. There is a significant linear modification of the effective
temperature with voltage due to the in-plane torque and a significant
contribution of a "field like" torque that is quadratic with voltage. The
methods presented here do not require complicated models for device heating or
calibration procedures, but instead directly measure how temperature, field,
and voltage influence the energy landscape and thermal fluctuations of a
two-state system. These results should have significant implications for
designs of future nanometer-scale magnetic random access memory elements and
provide a straightforward methodology to determine these parameters in other
MTJ device structures.
