Suppression of the spin waves nonreciprocity due to interfacial Dzyaloshinskii Moriya interaction by lateral confinement in magnetic nanostructures

TL;DR

This study investigates how lateral confinement in magnetic nanostructures suppresses the nonreciprocity of spin waves caused by interfacial Dzyaloshinskii Moriya interaction, revealing limitations of BLS in small elements.

Contribution

It provides experimental and simulation evidence that lateral confinement reduces spin wave nonreciprocity and affects the applicability of BLS-based iDMI quantification in nanostructures.

Findings

Suppression of frequency asymmetry in spin waves with decreasing lateral size.

Transition of spin wave character from propagating to stationary in confined structures.

Limitations of BLS method for measuring iDMI in structures smaller than 400 nm.

Abstract

Despite the huge recent interest towards chiral magnetism related to the interfacial Dzyaloshinskii Moriya interaction (iDMI) in layered systems, there is a lack of experimental data on the effect of iDMI on the spin waves eigenmodes of laterally confined nanostructures. Here we exploit Brillouin Light Scattering (BLS) to analyze the spin wave eigenmodes of non-interacting circular and elliptical dots, as well as of long stripes, patterned starting from a Pt(3.4 nm)/CoFeB(0.8 nm) bilayer, with lateral dimensions ranging from 100 nm to 400 nm. Our experimental results, corroborated by micromagnetic simulations based on the GPU-accelerated MuMax3 software package, provide evidence for a strong suppression of the frequency asymmetry between counter-propagating spin waves (corresponding to either Stokes or anti-Stokes peaks in BLS spectra), when the lateral confinement is reduced from 400 nm to 100 nm, i.e. when it becomes lower than the light wavelength. Such an evolution reflects the modification of the spin wave character from propagating to stationary and indicates that the BLS based method of quantifying the i-DMI strength from the frequency difference of counter propagating spin waves is not applicable in the case of magnetic elements with lateral dimension below about 400 nm.