Micromagnetic Simulations of Emission Power in Spin Torque Oscillator: Influence of Diameter and Interlayer Exchange Coupling

Micromagnetic simulations for spin torque oscillators (STOs) which have a perpendicular magnetized free layer (FL) and an in-plane magnetized reference layer (RL) in various diameters are presented. Our simulations show that an incoherent magnetization oscillation occurs at more than or equal to 350 nm in the diameter. Such incoherent magnetization oscillation causes the emission power of the STOs to be degraded. It is also indicated that not only is the magnetization dynamics of the FL related to the emission power but also the magnetization dynamics of the RL and the pinned layer are related to the emission power. In addition, it is revealed that changing the interlayer exchange coupling constant enhances the emission power.