Spin Valve Magneto-transport And Magnetic Study

Since the discovery of giant magnetoresistance (GMR) effect in 1988, much interest has been focused on the GMR of spin valves due to its applications in various fields and importance in basic research. First, as read head, spin valve devices are of crucial importance to the magnetic recording and the performance of read heads is strongly related to the GMR ratio and the sensitivity of spin valves. Magnetic and magneto-transport properties of spin valves depend not only on the structure, materials and thickness of constituent layers, but also on the fabrication process. Therefore, many attempts have been made in this field. Secondly, many physics issues in this community need further investigation. For example, as the key structure of spin valves, the mechanism of the exchange bias in ferromagnet (FM)/antiferromagnet (AFM) bilayers is still open.In this thesis, two important aspects were studied. First, the mechanism of coercivity enhancement in FM/AFM bilayers on silicon substrates and network templates was studied. Secondly, for spin valves, the effects of preparation process and interfacial roughness on the magneto-transport properties were studied as well as the contributions of spin dependent bulk-scattering and interfacial-scattering to the GMR ratio. The major results are summarized as follows:(1) First, the fabrication process has a great influence on the GMR ratio of the top-pinned spin valves. Secondly, through varying the FM layer thickness in Co/Cu/Co spin valves, it is found the GMR ratio is more sensitive to the bottom FM layer thickness than that of the top FM layer. This can be attributed to the effect of the interfacial roughness on the GMR ratio because the interfacial roughness varies with varying bottom layer thickness.(2) Using FM1/FM2/Cu/FM2/FM1 spin valves, where FM1 and FM2 can be Fe, Co, Ni, and Py, the contributions of the interfacial and bulk spin dependent scattering to the GMR ratio have been studied. For both the interfacial and bulk spin dependent scattering, the contribution decreases in the order of Co, Py, Fe, and Ni.