Micromagnetic study of spin wave transmission in bent ferrimagnetic strips

Abstract

Magnon propagation in antiferromagnetic (AFM) and/or ferrimagnetic (FiM) insulators is drawing attention due to the benefits as opposed to their ferromagnetic (FM) counterparts, such as higher fundamental frequency and insensitivity to external magnetic field perturbations. Spin wave (SW) propagation in these materials connects magnonics with spintronics, since spin current is mainly transported by magnons. A comprehensive study of the transmission of SWs in bent waveguides made of FiM material is made here. SWs are promoted by spin currents at one end of the guide and their transmission is measured at the other end. Current frequency is chosen to excite a single wavelength λ according to forward volume spin wave (FVSW) propagation dispersion curves. The guide has two bends at its center forming a certain angle and are distant a length apart. Both the angle and the distance are determinants on the transmission coefficient τ of the SW, defined from the quotient between the amplitude of the SW at the measurement point and the amplitude at a point at the same distance as the measurement point with respect to the excitation point in a strip without bends, i.e., without reflections associated with the geometry. Transmission minima and maxima are found for the different lengths between bends considered which coincide respectively with lengths equal to multiples of λ/2 and odd multiples of λ/4 , which is reminiscent of interferometry results for other types of guided waves, although in this case they are only explainable through an imaginary reflection coefficient at both bends.