Nanoconstriction-based spin-Hall oscillators

Recent observations of coherent microwave magnetization oscillations driven by pure spin current have provided novel opportunities for the development of active spintronic devices. It was demonstrated that pure spin current produced by the spin-Hall effect (SHE) can be utilized to implement magnetic nano-oscillators that do not require electrical current flows through the active magnetic layer, allowing one to avoid detrimental effects associated with large densities of the electric current in the magnetic layer typical for the traditional spin-transfer torque (STT) spintronic devices. The previously demonstrated spin-Hall nano-oscillators (SHNO) were found to exhibit a relatively large power and small auto-oscillation linewidth at cryogenic temperatures. However, both of these characteristics significantly degrade at increased temperatures. This drawback can be avoided if a single dynamical mode with a significant spatial extent can be selectively excited in an SHNO. One can expect that the auto-oscillation area should depend on the spin injection geometry. However, in practice local injection of spin current leads to the spontaneous formation of the so-called “bullet” auto-oscillation mode, whose spatial dimensions are determined by the nonlinear self-localization effects rather than the spin-current injection area. Here, we demonstrate SHNOs characterized by efficient room-temperature generation of coherent microwave signals, achieved by controlling the auto-oscillation characteristics using magnetic dipolar effects instead of the self-localization.