  Interfacial Dzyaloshinskii-Moriya interaction (iDMI) in interlayer exchange
coupled (IEC) Pt/Co$_{20}$Fe$_{60}$B$_{20}$(1.12
nm)/Ru/Co$_{20}$Fe$_{60}$B$_{20}$(1.12 nm) systems have been studied
theoretically and experimentally. Vibrating sample magnetometer has been used
to measure their magnetization at saturation and their interlayer exchange
coupling constants. These latter are found to be of an antiferromagnetic nature
for the investigated Ru range thickness (0.5-1 nm). Their dynamic magnetic
properties were studied using Brillouin light scattering (BLS) technique. The
BLS measurements reveal pronounced non-reciprocal spin waves propagation. In
contrast to the calculations for symmetrical IEC CoFeB layers, this
experimental nonreciprocity is Ru thickness and thus coupling strength
dependent. Therefore, to explain the experimental behaviour, a theoretical
model based on the perpendicular interface anisotropy difference between the
bottom and top CoFeB layers has been developed. We show that the Ru thickness
dependence of the spin wave non-reciprocity is well reproduced by considering a
constant iDMI and different perpendicular interfacial anisotropy fields between
the top and bottom CoFeB layers. This anisotropy difference has been confirmed
by the investigation of the CoFeB thickness dependence of effective
magnetization of Pt/CoFeB/Ru and Ru/CoFeB/MgO individual layers, where a linear
behaviour has been observed.
