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, theta(K), and ellipticity, epsilon(K), 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, theta(K)/epsilon(K) loops form inverse MR curves. The contrasting hysteresis behavior could be explained by the discriminate sensitivity of theta(K) and epsilon(K) 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 theta(K)(Co)/theta(K)(NiFe)=-1.4 and epsilon(K)(Co)/epsilon(K)(NiFe)=8.5. These values may allow one to understand the anomaly of the remarkably contrasting loops observed in NiFe/FeMn/Co trilayer films. (C) 2002 American Institute of Physics.