Magnon modes as a joint effect of surface ferromagnetism and spin-orbite coupling in CoSi chiral topological semimetal

TL;DR

This study reveals that magnon modes in CoSi chiral topological semimetals arise from the combined effects of surface ferromagnetism and strong spin-orbit coupling, impacting spintronic applications.

Contribution

It demonstrates the existence of magnon modes in CoSi due to surface ferromagnetism and spin-orbit coupling, a novel insight into its magnetic and transport properties.

Findings

Observation of $dV/dI$ curves similar to ferromagnetic multilayers.

Identification of magnon peaks and their magnetic field evolution.

Surface ferromagnetism and spin-orbit coupling jointly induce magnon modes.

Abstract

CoSi single crystal is a known realization of a chiral topological semimetal with simultaneously broken mirror and inversion symmetries. In addition to the symmetry-induced spin-orbit coupling, surface ferromagnetism is known in nominally diamagnetic CoSi structures, which appears due to the distorted bonds and ordered vacancies near the surface. We experimentally investigate electron transport through a thin CoSi flake at high current density. Surprisingly, we demonstrate $dV/dI(I)$ curves which are qualitatively similar to ones for ferromagnetic multilayers with characteristic $dV/dI$ magnon peaks and unconventional magnetic field evolution of the peaks' positions. We understand these observations as a result of current-induced spin polarization due to the significant spin-orbit coupling in CoSi. Scattering of non-equilibrium spin-polarized carriers within the surface ferromagnetic layer is responsible for the precessing spin-wave excitations, so the observed magnon modes are the joint effect of surface ferromagnetism and spin-orbit coupling in a CoSi chiral topological semimetal. Thus, thin CoSi flakes behave as magnetic conductors with broken inversion symmetry, which is important for different spintronic phenomena.