Field-free high-frequency exchange-spring spin-torque nano-oscillators

TL;DR

This paper introduces the first exchange-spring spin-torque nano-oscillators that operate at high frequencies without an external magnetic field, enabling more versatile and energy-efficient spintronic devices.

Contribution

It demonstrates a novel exchange-spring STNO design with high-frequency operation at zero magnetic field, expanding the potential for practical applications.

Findings

Operates at >10 GHz without external magnetic field

Exhibits exchange-spring dynamics and magnetic droplet solitons

Functions over a 20 GHz frequency range

Abstract

Spin-torque nano-oscillators (STNOs) are a type of nanoscale microwave auto-oscillators utilizing spin-torque to generate magnetodynamics with great promise for applications in microwaves, magnetic memory, and neuromorphic computing. Here, we report the first demonstration of exchange-spring STNOs, with an exchange-spring ([Co/Pd]-Co) reference layer and a perpendicular ([Co/Ni]) free layer. This magnetic configuration results in high-frequency (>10 GHz) microwave emission at a zero magnetic field and exchange-spring dynamics in the reference layer and the observation of magnetic droplet solitons in the free layer at different current polarities. Our demonstration of bipolar and field-free exchange-spring-based STNOs operating over a 20 GHz frequency range greatly extends the design freedom and functionality of the current STNO technology for energy-efficient high-frequency spintronic and neuromorphic applications.