9730908 Moodera This experimental research project is concerned with electron tunnel junctions with electrodes of magnetic metals conceived in such a way that the tunneling current is controlled in a sensitive fashion by an applied magnetic field. Well characterized ferromagnetic tunnel junctions and interfaces will be prepared under clean and ultra high vacuum conditions to allow accurate and reproducible tunneling measurements, particularly on structures with 3d and 4f ferromagnetic metals. Spin polarization of the same films that make up the tunnel junction will also be measured by superconducting tunneling spectroscopy. The main thrust is to understand the physical mechanisms responsible for the observed magnetic field sensitivity. It is expected that this research will additionally lead to new results and techniques in condensed matter physics and new applications for magnetic technology.This research program is interdisciplinary in nature and has typically involved several undergraduate and high school students in its activities. These involvements are beneficial in the preparation of students for further study and for careers in industry, government laboratories or academia. %%% This experimental research project is concerned with a new class of electronic devices that the PI has discovered in his previously supported work, which are highly sensitive to magnetic field. The electrical resistance of the device, which is called a tunnel junction, changes when the device is placed in a magnetic field, and is said to exhibit magnetoresistance. This discovery has created interest worldwide because of the potential for improvements in technology. The main technological applications may be in magnetic sensors for computer hard drives, possibly for magnetic computer memory or logic elements, and for miscellaneous applications s uch as sensors to measure rotational speeds, eg, a tachometer. The basic tunnel junction is a capacitor-like device with a thin insulating oxide between two metal plates. In this case the oxide layer is so thin that electrons can transfer from one plate to the other by the quantum mechanical tunneling process. This process was firmly established and understood in detail in the late 1960's by basic physics researchers who realized that a tunnel junction device, if it could be fabricated with a sufficiently thin and homogeneous oxide layer, could be instrumental to understanding the nature of superconductivity. Ivar Giaever won the Nobel Prize in Physics in 1973 for his experiments on superconductivity which were based on his development of improved fabrication techniques and a more complete understanding of the physical behavior of tunnel junctions. The present PI has gone on from these earlier basic research results to find the magnetic effects which are very promising for applications in computers and other technologies. As in the earlier case, the PI here has perfected new and more careful experimental methods to clearly reveal the theoretically expected physical effects, in this case magnetic in nature. This project focuses on careful and systematic measurements on junction structures with metal electrodes of different ferromagnetic compositions, in order to better understand and maximize the sensitivity to magnetic field. This research program is interdisciplinary in nature and has typically involved several undergraduate and high school students in its activities. These involvements are beneficial in the preparation of students for further study and for careers in industry, government laboratories or academia. ***
