Minimization of the Switching Time of a Synthetic Free Layer in   Thermally Assisted Spin Torque Switching
  We theoretically studied the thermally assisted spin torque switching of a synthetic free layer and showed that the switching time is minimized if the condition H_J=|H_s|/(2 alpha) is satisfied, where H_J, H_s and alpha are the coupling field of two ferromagnetic layers, the amplitude of the spin torque, and the Gilbert damping constant. We also showed that the coupling field of the synthetic free layer can be determined from the resonance frequencies of the spin-torque diode effect. 
Tomohiro Taniguchi and Hiroshi Imamura
cond-mat.mes-hall