Controllable spin modes created in nano-oscillator

The quasi-linear and bullet modes of magnetization have different characteristics, which are useful in applications such as for the generation of spin currents in magnetic nano-oscillators. New research reports a new way to manipulate the two modes of magnetization in nano-gap spin-Hall nano-oscillators—by controlling the geometry of the extended gap of the device. The new findings can be used to predict the preferential formation of one mode over the other, which will be useful in applications.

Divinskiy et al. tested devices created from a square bilayer of a platinum and Permalloy film. Two trapezoidal-shaped gold electrodes were separated by a gap to enable quasi-linear oscillation dynamics. Using micro-focus Brillouin light scattering spectroscopy, the researchers observed spin-Hall effect-induced auto-oscillations. Time-resolved measurements showed the quasi-linear mode began 100 nanoseconds before the bullet mode. The delayed onset of the bullet mode showed the two modes are formed by fundamentally different mechanisms. The researchers found the delay could be manipulated by varying the driving current, and that the quasi-linear mode dominated at low current, while the bullet mode dominated at higher currents.

In addition to providing new insight into the formation and stabilization of nonlinear magnon condensates, the new findings can be useful for practical applications such as nano-scale microwave sources, as the quasi-linear modes dominance at low currents can be used for generating short microwave pulses.

Source: “Controllable excitation of quasi-linear and bullet modes in a spin-Hall nano-oscillator,” by B. Divinskiy, V. E. Demidov, S. Urazhdin, R. Freeman, A. B. Rinkevich, and S. O. Demokritov, Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5064841 .