Magnetoresistance of stray-field coupled films

The magnetoresistance effect is used as an experimental tool in the investigation of the mechanism of magnetic coupling in multilayer films with intermediate laminations of electric insulating materials. The analysis of the shape of the hysteresis loops of the magnetoresistance can provide information about the inhomogeneous magnetization of such films. The films consisted of a soft layer of NiFe and a hard layer of Co, separated by approximately 1000 Å of SiO. Shifted hysteresis loops, indicating the presence of a unidirectional anisotropy, were observed when the driving field had a small amplitude. However, with increasing drive amplitude these loops became regular, and the existence of a field dependent uniaxial anisotropy was demonstrated. Both kinds of anisotropies are discussed in terms of stray field effects introduced by the initially polarized hard layer. With films whose ferromagnetic layers have nearly perpendicular easy axes, one obtains asymmetric magnetoresistance loops for some orientations of the driving field. These loops were attributed to the inhomogeneous distribution of the magnetization vectors within the laminations of the coupled films. This new method of investigation of the magnetic behavior of coupled films seems to be preferable to other methods when the ferromagnetic layers of the films are very thin.