Comparison of spin-wave transmission in parallel and antiparallel magnetic configurations

TL;DR

This study provides a theoretical analysis of spin-wave transmission in magnetic heterostructures with parallel and antiparallel configurations, revealing critical angles, polarization effects, and evanescent wave behavior relevant for magnonic device design.

Contribution

It introduces analytical boundary conditions and transmission coefficients for spin waves in P and AP configurations, highlighting polarization-dependent scattering and the role of critical angles.

Findings

Critical angle influences spin-wave transmission in P configuration.

Total reflection in AP configuration is polarization-independent.

Evanescent transmitted waves occur when incident angle exceeds critical angle.

Abstract

Parallel (P) and antiparallel (AP) configurations are widely applied in magnetic heterostructures and have significant impacts on the spin-wave transmission in magnonic devices. In the present study, a theoretical investigation was conducted into the transmission of exchange-dominated spin waves with nanoscale wavelengths in a type of heterostructure including two magnetic media, of which the magnetization state can be set to the P (AP) configuration by ferromagnetic (antiferromagnetic) interfacial exchange coupling (IEC). The boundary conditions in P and AP cases were derived, by which the transmission and reflection coefficients of spin waves were analytically given and numerically calculated. In the P configuration, a critical angle $\theta_{\textrm{c}}$ always exists and has a significant influence on the transmission. Spin waves are refracted and reflected when the incident angle $\theta_{\textrm{i}}$ is smaller than the critical angle ($\theta_{\textrm{i}} < \theta_{\textrm{c}}$), while total reflection occurs as $\theta_{\textrm{i}} \geq \theta_{\textrm{c}}$. In the AP configuration, the spin-wave polarizations of medium 1 and 2 are inverse, that is, right-handed (RH) and left-handed (LH), leading to the total reflection being independent of $\theta_{\textrm{i}}$. As demonstrated by the difference in spin-wave transmission properties between the P ($\theta_{\textrm{i}} < \theta_{\textrm{c}}$) and AP cases, there is a polarization-dependent scattering. However, as $\theta_{\textrm{i}}$ exceeds $\theta_{\textrm{c}}$, the P ($\theta_{\textrm{i}} > \theta_{\textrm{c}}$) case exhibits similarities with the AP case, where the transmitted waves are found to be evanescent in medium 2 and their decay lengths are investigated.