  Co2FeAl (CFA) ultrathin films, of various thicknesses (0.9 nm<tCFA<1.8 nm),
have been grown by sputtering on Si substrates, using Ir as a buffer layer. The
magnetic properties of the structures have been studied by vibrating sample
magnetometry (VSM), miscrostrip ferromagnetic resonance (MS-FMR) and Brillouin
light scattering (BLS) in the Damon-Eshbach geometry. VSM characterizations
show that films are mostly in-plane magnetized and the perpendicular saturating
field increases with decreasing CFA thickness suggesting the existence of
interface anisotropy. The presence of magnetic dead layers of 0.44 nm has been
detected by VSM. The MS-FMR with perpendicular applied magnetic field has been
used to determine the gyromagnetic factor. The BLS measurements reveal a
pronounced nonreciprocal spin waves propagation, due to the interfacial
Dzyaloshinskii-Moriya interaction (DMI) induced by Ir interface with CFA, which
increases with decreasing CFA thickness. The DMI sign has been found to be the
same (negative) as that of Pt/Co, in contrast to the ab-initio calculation on
Ir/Co. The thickness dependence of the effective DMI constant shows the
existence of two regimes similarly to that of the perpendicular anisotropy
constant. The DMI constant Ds was estimated to be -0.37 pJ/m for the thickest
samples where a linear thickness dependence of the effective DMI constant has
been observed.
