Formation of chirality in propagating spin waves

A general approach to quantify chirality, or absence of parity symmetry, of spin waves has been developed and applied to spin waves propagating in obliquely magnetized ferromagnetic films. Using theoretical arguments and numerical calculations, it is shown that, upon increasing spin wave wavevector, initially achiral spin waves develop chiral properties through the “parity exchange” mechanism, which implies, in particular, that chiral spin waves appear in pairs. The most striking example of the parity exchange mechanism is the simultaneous formation of two chiral waves: the magnetostatic surface wave and the recently discovered heterosymmetric spin wave, which were previously considered independent of each other. Another manifestation of the parity exchange is the formation of strongly chiral waves near the anti-crossings of spin wave branches of unequal symmetry. These findings illustrate viable paths to engineering spin wave systems with prescribed chiral spectra that had not previously been considered.