Ultra-high-frequency spin transfer torque nano-oscillators with skyrmion interlocked multi-channels

Spin transfer torque nano oscillators(STNO) with skyrmion-based bilayer structures serve as a propelling source for tunable microwave generators, delivering enhanced output power compared to conventional spin transfer torque nano-oscillators[1,2]. We propose a multi-channel skyrmion-based STNO design that mitigates the issue of skyrmion annihilation associated with monolayer skyrmion-based oscillators, ensuring a gyrotropic trajectory even with increased current application. Our design integrates high uniaxial anisotropy to create multiple tracks enabling skyrmion-interlocking, and facilitating ultrahigh-frequency operation with a single device. We observed that the skyrmion velocity depends on the input spin current, regardless of the skyrmion pair radius of rotation. Our oscillator reported a ~342 times frequency improvement compared to a monolayer single skyrmion oscillator, enhancing the operational frequency range from 0 to 41 GHz using our multi-channel design with multiple skyrmions. The proposed designs provide a versatile and robust structure taking into account the spin-flip length of the spacer material (Ru) for controlled and fine-tuned STNOs, thereby expanding the possibilities for skyrmion-based ultra-tunable microwave generators for various applications.

[1]Das et.al.,Skyrmion based spin-torque nano-oscillator,J. Magn. Magn. Mater(2019).

[2]Shen et. al.,Spin torque nano-oscillators based on antiferromagnetic skyrmions.APL(2019).