Using the anisotropic magnetoresistance technique on exchange biased bilayers with dispersed pinning

Although originally discovered more than 40 years ago, the physics behind the exchange anisotropy exhibited at the interface between an antiferromagnet and a ferromagnet is still poorly understood. Recent interest in exchange bias is motivated by the ubiquitous use of exchange biased materials in magnetic sensing elements, as well as by novel advances in our ability to probe interfaces within solid state materials.; The present research focuses on the exchange bias effect in industry-applicable samples (i.e., thin film magnetic materials that exhibit exchange bias at and above room temperature), and specifically investigates the behavior of interfacial magnetic moments using the anisotropy magnetoresistance (AMR) technique. Within this thesis a review of contemporary literature is presented, including the current theoretical and experimental progress in understanding the physics behind exchange bias. The AMR technique will be explained in detail, as will the variety of other techniques used to characterize the materials used in this research. The AMR measurements are then presented in conjunction with data simulated using a log-normal distribution in the pinning field. It is through this comparison that the most interesting conclusions of this dissertation are reached. Most importantly, that if the results of the AMR technique show a dependence on the applied magnetic field used to do the measurement, it is likely that the samples have dispersed pinning at the ferromagnetic/antiferromagnetic interface. Furthermore, it is shown that the results of AMR measurements on samples that have this type of dispersion are highly dependent on the applied magnetic field used to make the AMR loop. This is especially true at low applied fields where the dispersion can cause a misleading measurement of the exchange anisotropy field by as much as 25%.