Layer-dependent magnon-magnon coupling in a synthetic antiferromagnet
Yaqi Rong, Chengxin Jiang, Huishan Wang, Lu Sun, Fengyu Liu, Juanjuan Lu, Tao Wu, Yu Zhang, Yunshan Zhao, Fusheng Ma, Zhiqiang Mu, Haomin Wang, Yumeng Yang
Abstract
The synthetic antiferromagnet (SAF) offers a versatile platform to couple with various quasiparticles that is an indispensable element for the realization of hybrid quantum computing systems. In this work, we found that the magnon-magnon coupling strength in layered SAFs, consisting of repeated layers of $[{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/\mathrm{Ru}{]}_{n}$, is highly dependent on the finite layer number n. In particular, the self-hybridizations of individual acoustic or optical modes in the even-layers lead to the opening of local anticrossing gaps within the same type of mode in the resonance spectra. With the structural asymmetry of the odd-layers, a global gap between different modes can be generated whose size is found to decrease with increasing layer number. By combining the static linear chain model with the dynamically coupled Landau-Lifshitz equations, we further formulated a theoretical approach to qualitatively describe such highly layer-dependent behaviors of magnon-magnon coupling in SAFs. It is clear that the layer number is a significant factor that influences both the number of excited modes and the associated mode hybridizations. Our findings shed light on the magnon-magnon coupling in layered antiferromagnets that may invigorate the development of magnonics.