Spin–orbit torque driven nano-oscillators based on synthetic Néel-like skyrmion in magnetic tunnel junction

Abstract

A synthetic skyrmion-based magnetic tunnel junction spintronic nano-oscillator is proposed. The oscillator consists of a Pt/Co/AlOx/Co heterostructure. It exploits the high-frequency eigenoscillations of a synthetic chiral nanomagnet, which is imprinted in the Pt/Co layer by the local manipulation of the magnetic anisotropy and interfacial Dzyaloshinskii–Moriya interaction. This synthetic nanomagnet has the spin texture equivalent to the Néel skyrmion, and its topological stabilization remains resilient with respect to the thermal fluctuations at finite temperatures. The oscillator is activated by spin Hall effect-induced spin–orbit torques, and an eigenoscillation with a frequency of ∼2.5 GHz is achieved. When the drive current exceeds a threshold value, the eigenfrequency shifts toward lower frequencies. This redshift is associated with the transition of skyrmion dynamics, in which its eigenmode evolves from the counter-clockwise rotation mode to a complex hybrid mode. Our result verifies the working performance of the proposed synthetic skyrmion-based oscillator and suggests promising prospects for using such artificial nanomagnets in future spintronic applications. It is also found that the synthetic skyrmions are topologically protected from annihilation under high drive currents and finite temperatures, and this resilience, thus, offers new opportunities to better design next generation skyrmion-based spintronic devices.