Spin-resolved inelastic electron scattering by spin waves in noncollinear magnets

TL;DR

This paper proposes a novel inelastic electron scattering technique with spin analysis to probe and distinguish spin-wave excitations in non-collinear magnetic systems, including skyrmion lattices and spin spirals.

Contribution

It introduces a spin-polarized electron-energy-loss spectroscopy method with a spin-analyzer to detect and analyze spin-waves in non-collinear magnets, revealing new excitation mechanisms.

Findings

Spin-waves can be excited even via non spin-flip processes in non-collinear magnets.

The technique can distinguish different magnetic phases through dispersion and lifetime measurements.

It provides a way to probe large wave-vector spin-waves in low-dimensional systems.

Abstract

Topological non-collinear magnetic phases of matter are at the heart of many proposals for future information nanotechnology, with novel device concepts based on ultra-thin films and nanowires. Their operation requires understanding and control of the underlying dynamics, including excitations such as spin-waves. So far, no experimental technique has attempted to probe large wave-vector spin-waves in non-collinear low-dimensional systems. In this work, we explain how inelastic electron scattering, being suitable for investigations of surfaces and thin films, can detect the collective spin-excitation spectra of non-collinear magnets. To reveal the particularities of spin-waves in such non-collinear samples, we propose the usage of spin-polarized electron-energy-loss spectroscopy augmented with a spin-analyzer. With the spin-analyzer detecting the polarization of the scattered electrons, four spin-dependent scattering channels are defined, which allow to filter and select specific spin-wave modes. We take as examples a topological non-trivial skyrmion lattice, a spin-spiral phase and the conventional ferromagnet. Then we demonstrate that, counter-intuitively and in contrast to the ferromagnetic case, even non spin-flip processes can generate spin-waves in non-collinear substrates. The measured dispersion and lifetime of the excitation modes permit to fingerprint the magnetic nature of the substrate.