Direct dynamic imaging of non-adiabatic spin torque effects

Area of Science:

• Spintronics
• Condensed Matter Physics
• Materials Science

Background:

• Spin-transfer torques are crucial for spintronic devices.
• The non-adiabatic spin torque contribution is not fully understood.
• Existing theories attribute it to dissipation or magnetization gradient symmetry.

Purpose of the Study:

• To precisely determine the non-adiabatic spin torque parameter (β).
• To differentiate non-adiabatic spin torque from other influences using dynamic excitation.
• To establish a robust method for characterizing spin torque dynamics.

Main Methods:

• Utilized Lorentz microscopy combined with gigahertz excitations.
• Mapped the orbit of a magnetic vortex core with sub-5 nm resolution.
• Analyzed gyrotropic motion under dynamic excitation, including resonance conditions.

Main Results:

• Precisely determined the non-adiabatic spin torque parameter β = 0.15 ± 0.02.
• Observed subtle changes in vortex core orbit (ellipticity, amplitude, tilt) during resonant excitation.
• Demonstrated a method independent of external influences for accurate parameter determination.

Conclusions:

• The study provides an unprecedentedly precise value for the non-adiabatic spin torque parameter.
• Enhanced magnetic imaging under dynamic excitation is a powerful tool for spintronics research.
• This work clarifies the nature of non-adiabatic spin torques, advancing spintronic device development.