Breaking Space Inversion-Symmetry to Obtain Asymmetric Spin-Wave Excitation in Systems with Nonuniform Magnetic Exchange

TL;DR

This paper demonstrates that non-uniform magnetic exchange interactions can break space inversion symmetry, leading to asymmetric and nonreciprocal spin-wave excitations across a broad frequency range, with potential applications in magnonics and spintronics.

Contribution

It introduces a novel approach of using linearly varying exchange interactions to achieve symmetry-breaking and nonreciprocal spin-wave behavior in magnetic systems.

Findings

Non-uniform exchange induces asymmetric spin-wave modes.

Spatially-varying exchange enables tunable nonreciprocal excitation.

Nonreciprocity predicted up to hundreds of GHz.

Abstract

We report on the consequences of non-uniform exchange in magnetic systems. The quantum mechanical exchange interaction between spins is responsible for the phenomenon of magnetic order, and is generally considered to be uniform across bulk magnetic systems. Partly inspired by the Dzyaloshinskii-Moriya interaction--also known as antisymmetric exchange--we use a linearly varying exchange interaction along a magnetic strip as a route to spatial inversion symmetry-breaking. We find that, in addition to asymmetric modes and localization, spatially-varying exchange can be used to design nonreciprocal magnetic signal excitation at frequencies that are tunable. Moreover, our work predicts nonreciprocity to occur across a vast range of frequencies up to hundreds of GHz. Such spin wave engineering is a key area of ongoing research in the fields of magnonics and spintronics, which are expected to enable the next generation of communication technology. Analogous nonreciprocity is expected to occur in other wave systems with gradient properties.