Magnon dynamics in a ferromagnetic domain wall lattice: nonreciprocity without DMI

Nonreciprocal spin wave propagation may have useful applications in signal processing [1]. A nonreciprocal magnon dispersion, i.e. E(-k) ≠ E(k), is commonly induced by SOC in noncentrosymmetric systems, which results in a Dzyaloshinskii–Moriya interaction (DMI) term in the effective spin Hamiltonian [2]. We use a centrosymmetric Hamiltonian and induce a nonreciprocal dispersion without DMI. We consider steady state solution with injected domain walls, which can be sustained with interfacial spin transfer torques [3]. The nonreciprocal magnon dispersion is tunable and can be induced by an applied magnetic field perpendicular to the easy plane. We provide analytical solutions for the spin wave modes in the presence of in-plane anisotropy and weak magnetic fields. Numerical simulations confirm the results and explore beyond the analytics regimes.

[1] Jiahao Han, Yabin Fan, Brooke C. McGoldrick, Joseph Finley, Justin T. Hou, Pengxiang Zhang, and Luqiao Liu (2021), Nano Letters 2021 21 (16), 7037-7043

[2] Taku J Sato and Kittiwit Matan (2019) , Journal of the Physical Society of Japan, 88, 081007

[3] Daniel Hill, Se Kwon Kim, and Yaroslav Tserkovnyak (2018), Physical Review Letters 121, 037202