The interfacial Dzyaloshinskii-Moriya interaction (iDMI) has been investigated in Co 2 FeAl (CFA) ultrathin films of various thicknesses (0.8 nm≤t CFA ≤2 nm) grown by sputtering on Si substrates, using Pt, W, Ir and MgO buffer or/and capping layers. Vibrating sample magnetometry (VSM) revealed that magnetization at saturation (M s ) for the Pt and Ir buffered films is higher than the usual M s of CFA due to the proximity induced magnetization (PIM) in Ir and Pt, estimated to be 19% and 27%, respectively. The presence of PIM in these materials is confirmed using x-ray resonant magnetic reflectivity. Moreover, while no PIM is induced in W, higher PIM is obtained with Pt when it is used as buffer layer rather than capping layer. Brillouin light scattering (BLS) in the Damon-Eshbach geometry has been used to investigate the thickness dependencies of iDMI constants, from the spin waves non-reciprocity, and the perpendicular anisotropy field versus the annealing temperature. The DMI sign has been found to be negative for Pt/CFA and Ir/CFA while it is positive for W/CFA. The thickness dependence of the effective iDMI constant for stacks involving Pt and W shows the existence of two regimes similarly to that

Abstract-Interfacial Dzyaloshinskii-Moriya interaction (iDMI) in interlayer exchangecoupled (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. * belmeguenai.mohamed@univ-paris13.fr, 2 I-IntroductionThe exchange interaction plays an important role in magnetism and therefore is responsible of several phenomena in magnetic materials. This interaction can be direct (involving an overlap of electron wave functions from the neighboring atoms and Coulomb electrostatic interaction) or indirect (little or no direct overlap between neighboring electrons and mediated through an intermediary atoms). The direct exchange interaction between electrons arises from the Coulomb interaction and is responsible for the microscopic magnetic having the same wavelength and propagating along two opposite directions [9]. It is manifested by a difference between the frequencies of these two SWs. The DMI constant determination is thus reduced to this simple frequency difference measurement. Several experimental methods [10][11][12], largely based on how this interaction alters the properties of domain walls, were employed recently but Brillouin light scattering (BLS) spectroscopy remains the most direct method for DMI characterization. This scheme is simple, efficient, reliable and straightforward since few parameters are required for the experimental data fit [13,14]. It also allows the investigation of both in-plane and perpendicular spontaneously magnetized films in contrast to domain wall techniques. DMI can be induced by a lack of inversion symmetry of the compound and a strong spin-orbit coupling. This can be achieved by using heavy metal/ferromagnet (HM/FM) heterostructures, giving rise to interfacial DMI. 3Indirect exchange interactions such as coupling between two ...