Spin superfluid junction oscillator*

A spin oscillator is proposed based on a spin superfluid junction composed of two exchange coupled easy-plane ferromagnets. A spin chemical potential across the junction, with its spin polarization perpendicular to the easy-plane, can be established by driving electrical currents through two heavy metal contacts. When the spin chemical potential exceeds the threshold, it drives steady-state spin oscillation with a 2π precession angle, which can be electrically measured by the giant magnetoresistance, the anisotropic magnetoresistance, and the inverse spin Hall effect. The oscillation amplitude and frequency can be tuned via the applied D.C. current. An A.C. current applied to the heavy metal contacts, the spin oscillation also exhibits Shapiro steps, whose time-averaged component is fixed by the mode-locking. These features provide signatures for the experimental verification of spin superfluidity in easy-plane ferromagnets. This new type of spin nano-oscillator could serve as a device in a spintronic based neuromoprhic computing scheme.