Macrospin model of incubation delay due to the field-like spin transfer   torque
  We show that the absence of pre-switching oscillations ("incubation delay") in magnetic tunnel junctions can be explained within the macrospin model by a sizable field-like component of the spin-transfer torque. It is further suggested that measurements of the voltage dependence of tunnel junction switching time in the presence of external easy axis magnetic fields can be used to determine the magnitude and voltage dependence of the field-like torque. 
Samir Garzon, Yaroslaw Bazaliy, Richard A. Webb, Thomas M. Crawford,   Mark Covington, Shehzaad Kaka