Nanoconstriction-based Spin Hall nanooscillator

We experimentally demonstrate coherent magnetization oscillations induced in a bow tie-shaped Pt/Permalloy nanoconstriction by pure spin current generated by the spin Hall effect. The devices generate microwave signals with a significant power and the spectral linewidth as low as 6.2 MHz at room temperature (RT). In contrast to the previously demonstrated spin Hall oscillators governed by the dynamical nonlinear self-localization mechanism, the localized oscillation mode is present in the thermal fluctuation spectrum even below the auto-oscillation onset and exhibits a significant redshift. These observations suggest that the localized auto-oscillation mode is formed due to the confinement in an effective potential well produced by a combination of the dipolar field of the magnetic nanoconstriction and the Oersted field of electrical current. The studied devices are characterized by a large oscillation area, minimizing the effects of thermal fluctuations and resulting in a narrow RT spectral linewidth without compromising the single-mode regime of autooscillation. Moreover, the simple planar structure of the proposed oscillators enables their cascading, which can be utilized to further improve the oscillation characteristics in mutually coupled devices.