title: Direct dynamic imaging of non-adiabatic spin torque effects.
abstract: Spin-transfer torques offer great promise for the development of spin-based devices. The effects of spin-transfer torques are typically analysed in terms of adiabatic and non-adiabatic contributions. Currently, a comprehensive interpretation of the non-adiabatic term remains elusive, with suggestions that it may arise from universal effects related to dissipation processes in spin dynamics, while other studies indicate a strong influence from the symmetry of magnetization gradients. Here we show that enhanced magnetic imaging under dynamic excitation can be used to differentiate between non-adiabatic spin-torque and extraneous influences. We combine Lorentz microscopy with gigahertz excitations to map the orbit of a magnetic vortex core with <5 nm resolution. Imaging of the gyrotropic motion reveals subtle changes in the ellipticity, amplitude and tilt of the orbit as the vortex is driven through resonance, providing a robust method to determine the non-adiabatic spin torque parameter β=0.15±0.02 with unprecedented precision, independent of external effects.
authors.affiliation: Department of Condensed Matter Physics, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Pollard
authors.forename: L
authors.initials: L
authors.lastname: Huang
authors.forename: K S
authors.initials: KS
authors.lastname: Buchanan
authors.forename: D A
authors.initials: DA
authors.lastname: Arena
authors.forename: Y
authors.initials: Y
authors.lastname: Zhu