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

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.