Mode coupling in a two-mode spin-torque oscillator: coexistence, mode-hopping and linewidth broadening

Spin-torque oscillators (STOs) are microwave frequency and spin-wave generators with potential technological applications. Single-mode oscillators have been described previously[1]. However, recent experiments have shown STO multi-mode generation [2,3]. By extending the single-mode auto-oscillator theory [1] taking into account mode coupling, we show that single-mode generation, coexistence, and periodic energy transfer are possible to describe analytically. Furthermore, the generation linewidth in a mode-hopping regime exhibits broadening due to the autocorrelation loss, similar to a thermally-driven particle in a double potential well obeying Arrhenius' equation. Our results provide the physical mechanism behind the linewidth broadening at current and temperature driven mode transitions. Argonne National Laboratory is a US DOE Science Laboratory operated under Contract No. DE-AC02-06CH11357 by UChicago Argonne, LLC. Supported by grants from the Swedish Research Council (VR), the Swedish Foundation for Strategic Research (SSF), and the Knut and Alice Wallenberg Foundation. References: [1] Slavin and Tiberkevich, IEEE Trans. Magn. \textbf{45}, 1875 (2009). [2] Muduli et al., Phys. Rev. B \textbf{86}, 174408 (2012); Dumas et al., Phys. Rev. Lett. \textbf{110}, 257202 (2013). [3] Muduli et al., Phys. Rev. Lett. \textbf{108}, 207203 (2012).