Magnetic Y-Branch Nanojunctions: Engineering Magnetism Through Nanoscale Design
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In this thesis we introduce a specially-designed nanomagnetic Y-branch junction (YBJ), whose critical region is formed by the intersection of a pair of nanoscale notches. The device was fabricated in polycrystalline cobalt by electron-beam lithography and lift-off. Room temperature magnetoresistance (MR) was measured at room temperature using an electromagnet system that allowed the field to be applied at arbitrary directions with respect to the device. The resulting magnetic domain structures formed in the YBJ were analyzed through micromagnetic modeling (OOMMF), magnetic force microscopy (MFM) and MR studies. The latter measurements revealed several features distinct from the well-known anisotropic MR (AMR), including antisymmetric MR, more normally associated with magnetic multilayers, and asymmetric MR structures. None of these features were found in measurements of bars with single notches, indicating that they result from the unique features of the YBJ geometry. In this geometry, we suggest that phenomena arising from complicated frustration of the magnetism can play an important role. A proper understanding of these phenomena may ultimately help in the development of new MR sensors, and spintronic devices, for application to different magneto-electronic technologies.