Spectrum of exchange spin waves in a one-dimensional magnonic crystal with antiferromagnetic ordering

Abstract

Purpose of the study is to show that the conditions for the propagation of exchanged spin waves (ESWs) in an asymmetric superlattice with antiferromagnetically ordered cells depend significantly on the chirality of the precession of the ESW magnetization (polarization, “magnon pseudospin”). Method. When constructing the EWS spectra, the Croning– Penny model (transfer-matrix method) and the Landau–Lifshitz equation are used to determine the nature of the waves in the cells. In the case of a uniaxial medium, there is only one type of ESW, therefore, when fields are joined at the boundary, the conservation of chirality is an essential factor due to which the ESW in one cell is always traveling, and in the other — evanescent. Thus, a superlattice for ESW is an effective periodic “potential” in which asymmetry can be realized either by applying an external field, or by a difference in the thickness and/or physical properties of the cell materials. Results. Based on the analysis of the spectrum, maps of the transmission zones for ESW of different chirality were constructed in three representations — “Bloch wave number – frequency”, “frequency – relative cell thickness”, as well as in the plane of cell wave numbers. It is shown that the presence of asymmetry leads to a difference in the width of the transmission zones for waves of different chirality. For a finite structure, the frequency dependences of the transmission and reflection coefficients of the ESW are plotted. An increase in the attenuation of the ESW near the boundaries of the transmission zones was also found. Conclusion. The results of the study can be used in the design of magnon valves and other devices based on ESW, in which their chirality can be controlled.