Ballistic electron magnetic microscopy: Hot-electron transport studies and magnetic imaging of ferromagnetic multilayer films, nanostructures, and tunnel junctions.

摘要

This dissertation describes the development of a new magnetic imaging technique, ballistic electron magnetic microscopy (BEMM), and its application to thin ferromagnetic films. Using this technique, the magnetic behavior of both continuous and patterned ferromagnetic multilayer films has been studied as a function of applied magnetic field. The typical domain size in these thin films is found to be ∼500–1000 nm, although much smaller magnetic structures are commonly observed. It is demonstrated that the switching of magnetic nanostructures can generally be controlled by applying modest magnetic fields, although occasionally the reversal process is hindered by the formation of 360° domain walls in the interiors of the elements. Thermally assisted domain wall motion is also found to play a role in the magnetization reversal process, particularly in permalloy nanostructures.; The hot-electron scattering properties of thin Co and permalloy films have also been studied. Specifically, the inelastic scattering lengths of both majority and minority electrons in Co have been determined as a function of electron energy over the range of 1.0 to 2.0 eV above the Fermi energy. The cumulative spin-filtering effects of spin-dependent tunneling to Co and subsequent transmission across a Co/Cu interface have been measured over this same energy range. Studies on films prepared both by thermal evaporation and sputter deposition have been performed. While the magnetic behavior of the films prepared by the two different deposition methods has been found to be very similar, the details of current transport in films prepared by the two techniques are distinctly different.; Electron transport through thin AlO_x based magnetic tunnel junctions has also been studied at the nanometer length scale. The effective barrier height of these insulating barriers has been determined to be 1.25 ± 0.5 eV. The transmission probability of hot electrons through these barriers has also been measured. Tunnel junctions prepared by thermal evaporation and sputter deposition are compared. While the effective barrier height of junctions formed by the two techniques are very similar, the electron transmission probabilities through the two types of barriers are different.