Field-Free Mutual Synchronization of Parallel Coupled Spin Torque Nano Oscillators Using a Free Layer With First- and Second-Order Uniaxial Anisotropy

The synchronization behavior of two spin torque nano oscillators (STNOs) with second-order anisotropy, connected via parallel coupling, has been studied in the presence of the thermal field. The second-order anisotropy led to the biasing of the free layer (FL) of both the STNOs in the easy cone regime called the conical FL (CFL). This parallel coupling facilitated frequency and in-phase synchronization between the two STNOs without the need for any external field. The simulation results demonstrating this in-phase synchronization have been supported by analytical theory. Further, the effects of parallel coupling on oscillation parameters, such as frequency, power, and linewidth, have been examined. The variation of the frequency with current and the coupling factor has been derived using the LLGS equation. The study achieved a threefold increase in output power and a reduction in linewidth to the order of kHz, without requiring an external field. These advancements highlight the potential of the device for reliable practical applications.