Role of Magnetic Field in Self-Oscillation of Nanomagnet Excited by Spin   Torque
  The critical current of the self-oscillation of spin torque oscillator (STO) consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer was studied by solving the Landau-Lifshitz-Gilbert (LLG) equation. We found that the critical current diverged at certain field directions, indicating that the self-oscillation does not occur at these directions. It was also found that the sign of the critical current changed depending on the applied field direction. 
Tomohiro Taniguchi, Shingo Tamaru, Hiroko Arai, Sumito Tsunegi,   Hitoshi Kubota, and Hiroshi Imamura
cond-mat.mes-hall