Magnetic and transport studies of thin film ferromagnetic nanostructures

My thesis has involved experimental studies of the magnetic and transport properties of thin film ferromagnetic elements, produced by optical and electron beam lithography. It consists of three related parts: (1) domain wall scattering of conduction electrons, (2) studies of magnetization reversal in thin film nanostructures and (3) exchange biasing in ferromagnetic/antiferromagnetic nanostructures. In each instance, model thin film structures have been developed to study the effects of finite size on these properties, i.e. how the element size, shape and boundaries or interfaces affect their magnetic and transport characteristics.; Electronic transport experiments have been performed on ferromagnetic wires with controlled domain configurations. I have studied three different materials of progressively higher magnetic anisotropy: (110) oriented bcc Fe films, hcp Co films and MBE L1₀ FePt films. By studying the conventional sources of magnetoresistance and isolating the contribution of the domain walls to resistance, I found that domain walls lead to a reduction of resistance in Fe wires, while in Co and FePt wires the resistance is increased with domain walls. I present physical models for these transport characteristics.; I have patterned epitaxial (110) bcc Fe and polycrystalline IrMn/CoFe thin films into elements with rectangular, triangular, and needle-shaped ends. Magnetic force microscope (MFM) imaging and longitudinal Kerr hysteresis loop measurements have been used to investigate the micromagnetic behavior. For Fe elements, the end shape is critical in determining domain nucleation, domain configurations and magnetic hysteresis, which indicates the important role of the demagnetizing field arising from the magnetic charges at the element boundaries. I found that patterning films to micron size does not significantly alter the exchange biasing phenomena in IrMn/CoFe elements. Size effects may become more pronounced at only the deep submicron level, as elements approach the domain sizes (∼50 nm) in the AF. My results suggest that the random nature of ferromagnetic/antiferromagnetic interactions is essential to model exchange biasing phenomenon.