Making the invisible visible: Spins probed with soft x-rays*

The advancement of spintronics relies on our improved understanding spin based phenomena and our ability to engineer materials with specific magnetic and transport properties. In this talk, we will highlight the contributions optimized soft x-ray based characterization tools can make to this endeavour.

Chiral domain walls are promising candidates for low-energy consumption memory and logic devices. We engineered chiral domain wall arrays in Pt/Co/Cu multilayers and using resonant soft X-ray diffraction find that the chirality of the magnetic spin textures in the surface near region reverses as function of layer thickness due to the interplay of competing driving forces (DMI, magnetic anisotropy, magnetic dipole interaction). [1]

The recent discovery of magnetic long-range order in two-dimensional van der Waals materials opens up new opportunities for spintronics. We employed soft X-ray photoemission electron microscopy (PEEM) to image the domain configuration of Fe₃GeTe₂. We find that the magnetic long-range order in micron scale Fe₃GeTe₂ pattern leads to an unconventional out-of-plane stripe-domain phase that undergoes a transition to an in-plane vortex phase with increasing temperature. [2]

Spin currents are mostly detected indirectly through measurement of spin-torque driven magnetization precession, spin-current induced second harmonic optical effects, inverse spin Hall effect (ISHE), etc. We have succeeded in monitoring a pure ac spin current directly through a Py/Cu/Co multilayer with by X-ray detected ferromagnetic resonance (XFMR). [3]

In this talk, the powerful X-ray instrumentation optimized for these studies of spintronics phenomena will be discussed.

References
[1] G. Chen, P. Shafer et al., under review.
[2] Q. Li et al., Nano Lett. 18, 5974 (2018)
[3] J. Li et al., Phys. Rev. Lett. 117, 076602 (2016)