Contrasting hysteresis behavior between the magneto-optical Kerr rotation and ellipticity in NiFe/FeMn/Co trilayer films

We report an experimental observation of strikingly contrasting hysteresis behaviors between the longitudinal magneto-optical Kerr rotation, θK, and ellipticity, eK, in NiFe/FeMn/Co films. For example, one is likely to reproduce a typical magnetic hysteresis loop obtainable with vibrating sample magnetometry while the other one does reproduce magnetoresistance (MR)-like curves in some cases. Interestingly, θK/eK loops form inverse MR curves. The contrasting hysteresis behavior could be explained by the discriminate sensitivity of θK and eK to the ferromagnetic NiFe as well as Co layers. Using a simple model, we determine the sensitivity ratios of the Co to NiFe layer for both signals, which are far from unity as much as θKCo/θKNiFe=−1.4 and eKCo/eKNiFe=8.5. These values may allow one to understand the anomaly of the remarkably contrasting loops observed in NiFe/FeMn/Co trilayer films.