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

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 ${\theta }_{\text{c}}$ always exists and has a significant influence on the transmission. Spin waves are refracted and reflected when the incident angle ${\theta }_{\text{i}}$ is smaller than the critical angle (${\theta }_{\text{i}}<{\theta }_{\text{c}}$), while total reflection occurs as ${\theta }_{\text{i}}\ge {\theta }_{\text{c}}$. 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 ${\theta }_{\text{i}}$. As demonstrated by the difference in spin-wave transmission properties between the P (${\theta }_{\text{i}}<{\theta }_{\text{c}}$) and AP cases, there is a polarization-dependent scattering. However, as ${\theta }_{\text{i}}$ exceeds ${\theta }_{\text{c}}$, the P (${\theta }_{\text{i}}>{\theta }_{\text{c}}$) 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.

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