Quantitative Study of Spin Wave Chirality in Obliquely Magnetized Magnetic Films

Dipole-dipole interaction in thin magnetic films leads to formation of parity-breaking (i.e., chiral) spin wave (SW) modes, such as, e.g., chiral magnetostatic surface SW (CMSSW) [1] & heterosymmetric SW (HSSW) [2] having a number of unique properties. However, a general theory of the origin of chiral spin wave formation & their chiral properties in obliquely magnetized magnetic films (OMMF) remains absent. Here, we propose a quantitative measure of SW chirality, C_n = 1 – │〈Ρ〉_n│, where 〈Ρ〉_n is the expected value of the parity operator for the n^th SW mode. Using Kalinikos-Slavin's theory of SW spectrum in OMMF [3], we performed quantitative study of formation of chiral SWs. We show that total parity ∑_n〈P〉_n of all SW modes is approximately conserved, which implies that SW modes acquire chiral properties in pairs through the “parity exchange” mechanism. In particular, we demonstrate formation of strongly chiral modes at odd crossing points of SW spectrum & show that chirality of both CMSSW & HSSW is a result of “parity exchange” between two lowest symmetric & antisymmetric SW modes.

[1] M. Mohseni et al., Phys. Rev. Lett. 122, 197201 (2019).

[2] G. Dieterle et al., Phys. Rev. Lett. 122, 117202 (2019).

[3] B.A. Kalinikos & A.N. Slavin, J. Phys. C: Solid State Phys. 19, 7013 (1986).