Magnetoresistance and magnetodynamics in thin-film magnetic heterostructures.

摘要

Current information technology relies heavily on magnetism. Gaining a deeper understanding of magnetism, and in particular spin dynamics, is important to today's quickly evolving technology. In this thesis, two separate studies have been conducted to help aid in the study of spin dynamics. The first project explores giant magnetoresistive (GMR) devices. These devices are presumed to be made of materials that are radiation hard with respect to both photons and particles, potentially increasing their utility for nuclear energy and space based applications. However, to date there are few detailed studies of magnetism and GMR devices in hard radiation environments. This project utilizes the facilities at The Ohio State University Nuclear Reactor Laboratory to study the effects of gamma ray and neutron irradiation on GMR samples. The structure used in this experiment is a standard GMR trilayer consisting of a thin, non-magnetic layer placed between thin ferromagnetic layers, with one of the two magnetic layers in contact with an exchange biased antiferromagnet (Py/Cu/Py/FeMn/Ge). To study the effects of radiation three types of magnetic measurements, vibrating sample magnetometery (VSM), magnetoresistance (MR), and magneto-optical Kerr effect (MOKE), are taken and correlated pre and post gamma radiation. We present characterization of the devices pre and post gamma irradiation for multiple device geometries and radiation doses up to 50 Mrad for gamma rays and a minimum fast flux (En>0.5MeV) of 4.2E12 nv for neutrons, both of which are well above the failure threshold for semiconducting devices. The second study that was done in this thesis uses current-induced magnetodynamics in giant magnetoresistive (GMR) trilayers. These devices promise a novel platform for microwave electronics. One of the keys to developing this potential has been the development of nanoscale fabrication techniques, typically resulting in either nanopillar or point-contact geometries. As a result, a considerable technical barrier to further progress is the fidelity of current nanoscale patterning techniques. In an effort to address this challenge, we present the results of development efforts aimed at fabricating prototype point-contact spin torque oscillator (PC-STO) structures with a focused ion beam (FIB). The flexibility of FIB-based nanofabrication allows in situ cross sectional imaging of contact structure, and these results are correlated with DC magnetotransport. This fabrication approach enables the rapid generation of structures in arbitrary geometries, and in conjunction with cross-sectional imaging promises increased control of device to device variation and the development of novel PC-STO structures.