The absence of giant magnetoresistance on antiferromagnetically coupled NiFe/Cr multilayers

Abstract

To further investigate the relationship between the giant magnetoresistance (GMR), anisotropic magnetoresistance (AMR), and antiferromagnetic (AFM) coupling found in magnetic multilayers we have deposited NiFe/Cr multilayers onto rectangular Corning 7059 glass substrates at ambient temperatures. Uniaxial anisotropy was induced by applying a 90 Oe field along the length of the substrate strips during deposition and in all cases a 50–100-Å-thick Cr underlayer was used. For Cr interfilms 9–12-Å thick, the multilayers were found to have hard axis saturation fields of 90–200 Oe and easy axis hysteresis loops which exhibit a complex behavior dependent on whether the multilayer is composed of an even or an odd number of NiFe films. Both of these effects result from AFM coupling of the NiFe films. The magnetoresistive (MR) behavior was also found to be complex and dependent on the number of NiFe films in the multilayer. A theoretical model based on coherent rotation and including AFM coupling between the NiFe films has been developed and both the hysteresis loops and MR of the multilayers calculated. From these calculations it has been found that, despite the existence of AFM coupling, the experimentally observed magnetoresistive behavior can be described using only AMR. Thus the existence of AFM coupling does not result in GMR NiFe/Cr multilayers. This is discussed in terms of spin filtering at the multilayer interfaces.