Investigation of magnetization reversal in chains of permalloy ellipses via magnetoresistance measurement and magnetic force microscopy

Abstract

The magnetization reversal processes of single and chained permalloy thin film ellipses were investigated by using magnetoresistance measurements and magnetic force microscopy. The permalloy ellipses with fixed short axis of 1 micrometer and various long axes of 6, 8, 10 micrometers, respectively, were fabricated by standard electron beam lithography through a lift-off process. It was found that the switching field increases with increasing the long axis of the ellipse in the case of single ellipse. The switching field of two ellipses in series is higher than that of each individual one. The stronger shape anisotropy is accounted for the increasing of switching field in longer element, in which two ellipse in series can be seen as a longer element as a whole. In the case of two identical and a longer ellipses in series, the switching field falls in-between those two measured on individual shorter and longer ones. Magnetic force microscopy reveals a wavelike domain configuration nucleated during magnetization reversal only in the middle one of three chained ellipses, in which this kind of non-coherent reversal process may contribute to the decreasing of the switching field.