Physics near the metal-insulator transition in magnetic thin-films

University Of Florida, Gainesville FL

Investigators

Abstract

****Technical Abstract**** For the traditional transition-metal band ferromagnets (Fe, Co and Ni) where the aligned moments are successfully described by unequally populated majority (spin-up) and minority (spin-down) bands, the ultimate fate of magnetism, when the itinerancy is compromised by disorder to such an extent that the conductivity drops to zero at critical disorder, is unknown. This project addresses the consequences of systematically reducing the thickness of two-dimensional (2D) magnetic thin films (thereby increasing disorder strength) until the insulating magnetic state is attained. A custom high-vacuum deposition system with in situ electronic/magnetic characterization capability prevents sample deterioration due to air exposure and is essential for this work. The project's focus on tuning a variety of magnetic systems through critical disorder is expected to provide valuable insight into the properties of thin-film magnetic insulators and help answer questions about (1) the disorder induced high rate of inelastic scattering of electrons off of spin waves, (2) the ordering of local moments, (3) the role of granularity, and (4) the emergence of new phases. This project will support the education of PhD students in advanced vacuum deposition and electronic/magnetic characterization techniques, which have already proven to be excellent training for productive scientific careers in academic and technology settings. Pursuit of these studies will improve prediction of the magnetic properties of ultrathin magnetic materials and extend knowledge of the behavior of bulk magnetism in the very different environments experienced at surfaces and interfaces. ****Non-Technical Abstract**** Magnetism in the transition metal elements such as iron is not fully understood. In the itinerant (traveling) electron scenario there are more spin-up (north pole up) than spin down (north pole down) electrons and the net difference gives rise to the magnetic properties that, for example, cause an iron compass needle to align with the earth's magnetic field. The situation rapidly becomes more complicated when the itinerant electrons scatter off impurities and/or defects, losing their itinerancy and eventually becoming localized (fixed in place) when the disorder strength, as characterized by the density of scattering sites, is at a critical value. This project will pursue experimental studies of magnetic thin films in which disorder can be systematically increased and the effect on magnetism studied. At critical disorder, itinerancy is lost and the magnetic metal becomes an insulator with localized electrons accompanied by the likely appearance of new magnetic phases with unusual spin alignments. This project will support the education of PhD students in advanced vacuum deposition and electronic/magnetic characterization techniques, which have already proven to be excellent training for productive scientific careers in academic and technology settings. The expected increased physical understanding of magnetism in thin films from these studies will be relevant to technological applications which incorporate ultrathin magnetic films into multilayer configurations for magnetic recording, spin generation, spin manipulation and/or spin detection.