Reinforcing spin wave non-reciprocity via multiple mechanisms*

We have studied spin wave propagation in exchange biased ferromagnet (FM) / antiferromagnet (AFM) bilayer systems with the Damon-Eshbach (DE) geometry which corresponds to n⊥M, n⊥k, and M⊥k where n is the film normal, k is the wavevector, and M is the magnetization. Due to pinned spins in the presence of the interlayer exchange interaction at FM / AFM interface, surface spin waves propagating along the FM / AFM interface were suppressed, resulting in spin wave non-reciprocity. Furthermore, we have shown that Oersted field from a patterned coplanar waveguide (CPW) on the film, in all possible four configurations (CPW above or below the FM / AFM bilayer or forward or reversed M), was always coupled strongly with a surface spin wave propagating on the opposite surface. Therefore, we have found that the CPW needs to be patterned on top of the AFM layer (FM / AFM / CPW) to make a geometry where different mechanisms for nonreciprocity ‘interfere constructively’. By using these two mechanisms at the same time, we have achieved enhanced nonreciprocity bigger than those achieved from either of single mechanism. We also found that in a ‘destructively interfering’ geometry nonreciprocity was smaller than those from either of the single mechanisms.