Ballistic magnetoresistance in ferromagnetic atomic point contacts
Sullivan, Matthew R.
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The field of nanotechnology and quantum devices is rapidly developing, with the aims of both miniaturizing current devices, and creating new devices for old and new applications alike. To date, devices have shown applications in a wide range of sensing and computing technologies. While several applications have come to the stage of commercialization, many more are stuck in the research and development stage due to a lack of repeatability. This is simply the result of the nature of such devices and the ability of a handful of impurity atoms to render a device inoperable, as well as the necessity for low temperature environments for many of these effects to be seen. In addition to this, many quantum effects are not fully understood, fueling intense debates and research to determine the true nature of the effects. This work is aimed at researching the true nature of one such quantum effect, and developing the early stages of a quantized magnetoresistance sensor. A microfabricated sensor was fabricated to replicate results earlier seen using wire samples using electrodeposited atomic point contacts. Several testing methods were used in order to observe changes in the conductance level of contacts, first applying a magnetic field to demonstrate the principle of ballistic magnetoresistance, as well as to provide evidence for the quantum mechanical behavior leading to this effect. During this process, histograms were collected at different field values to understand the effect of field on the conductance levels of said contacts made of nickel and cobalt. In this thesis, considerations for different methods on contact formation, as well as the fabrication techniques and testing methods are presented. Fundamental studies on quantized electron transport and ballistic magnetoresistance are presented as a basis for a novel magnetic sensor whose quantum effects are observable at room temperature. The significance of these results is finally discussed in its contribution to the understanding of quantum mechanical behavior, as well as the possibilities of the fabrication of a device controlled by the properties of a handful of atoms.