The main objective of this research is to develop instrumentation and models in order to study the Barkhausen effect both experimentally and theoretically. Another objective of this research is to investigate the effect of stress on magnetic properties of thin film using the micromagnetic (Landau-Lifschitz-Gilbert) modeling approach.;A new computer-controlled system has been developed to make Barkhausne emission (BE) measurement on materials. This system provides the capability for making BE measurements using various settings such as the parameters of the excitation field, and analyzing the results in a variety of ways including time and frequency domain analysis. Measurements can be made easily and rapidly through the use of system software. Inspection procedures were implemented into the software in modular form. New procedures can therefore be easily added, allowing evolution of the instrument to meet new needs.;In this study, the new system was used to study the relationship between the BE signal and the amount of material removed from the case-hardened steel. The results demonstrate conclusively the viability of using BE measurement for monitoring wear-induced material loss.;A non-linear Barkhausen model incorporating ideas from the previous models has been proposed in this study. The Jiles-Atherton hysteresis model was integrated into this new model to calculate the permeability. As a result, the new model allows for changes in permeability with applied field and can be used to investigate the Barkhausen effect signal according to the variations of the hysteresis loop.;Although stress has an important role in magnetism, it is surprising that modeling of magnetization processes in thin films in the presence of external stresses has received little attention. In order to investigate the stress effect in magnetic thin films, a new micromagnetic model based on the Landau-Lifschitz-Gilbert (LLG) equation has been developed. The modeling results show that the hysteresis loop properties, such as coercivity and remanence, should change drastically with applied stress and this is in good agreement with experimental observations.