Dependence Of The Magneto-Optical Signal On The Co Layer Thickness Asymmetry In Co/Pt/Co Films

We have studied the magneto-optical response of Co(t(1))/Pt(d)/Co(t(2)) trilayer structures, in which the total Co thickness (t(1) + t(2)) was held constant, but the split between the top and bottom layer made variable to investigate the impact of the Co layer thickness asymmetry a(t) = (t(1) - t(2))/(t(1) + t(2)) as well as the influence of the P-t interlayer thickness d. The optical and magneto-optical properties of these films were measured using generalized magneto-optical ellipsometry. A set of specifically designed inverted double-wedge structures were characterized to determine the influence of d and especially of at, which should be significant if quantum-well states are relevantly modified by the Co layer thickness asymmetry. In addition to a Co/Pt interface proximity effect that leads to an overall enhancement of the magneto-optical response, we do not find the expected quadratic at effect, but instead observe a strong linear at effect. We also compare our experimental results to a classical optics description based upon the transfer matrix method, but we can achieve agreement in between these calculations and our experimental data only if we assume massively anomalous optical wave attenuation in Pt. This perceived anomalous attenuation of Pt is not observed for Co/Pt/Co trilayer structures with much thicker Co films, in which quantum-well states should not be relevant anymore. Thus, the origin of the unexpected strong linear at effect in ultrathin Co/Pt/Co trilayers cannot be a local materials modification, but instead must be associated with the collective nature of quantum-mechanical electronic states in asymmetric trilayers.