Magnetic Phenomena on the Nanometer Scale

Johns Hopkins University, Baltimore MD

Investigators

Abstract

This research is focused on the investigation of the spin polarization of ferromagnetic metals and the switching of ferromagnetic components. These phenomena, occurring on the nanometer scale, are of crucial importance to magnetoelectronic devices. We propose to use the point-contact Andreev reflection technique, with appropriate analyses, to measure the intrinsic spin polarization of a variety of materials, especially CrO2 and the Heusler alloys, which have been predicted to be 100% spin polarized. We also propose to address key issues in multilayers with exchange bias, particularly the type of antiferromagnetic spin structure present, antiferromagnetic domains, and the switching of exchange-coupled systems using synthetic antiferromagnets. The graduate students involved in the project receive training in cutting-edge technology of careers in academe, industry and government. Magnetoelectronic devices are new devices that manipulate both spin (magnetic dipole moment) and charge of electrons as opposed to only charge of electrons in traditional electronic devises. These new devices depend crucially on the substantial spin polarization of certain ferromagnetic materials (a difference in the number of resident spin-up and spin-down electrons) through which the itinerant electrons flow, and the ability to switch the magnetization of the ferromagnet channels. Example of such devices employing these components include giant magnetoresistance (GMR) read-heads in virtually all computers manufactured today, and magnetic random access memories (MRAM) that one day may be replace the current dynamic random access memory (DRAM) used in current computers. This work is directed at measuring the intrinsic spin polarization of metals (the ferromagnetic channels) using the technique of Andreev reflection, which depends on fundamental properties of superconducting junctions that are employed in the experiments. The other part of this work is to understand how thin magnetic layers, which exist in many magnetoelectronic devices, can be made to switch easily by a small external field, or be designed to resist switching. Students in this program will receive extensive training in physics, new materials, and measuring techniques to enable them to pursue careers in academe, as well as in industrial and government labs.