Perpendicular-Current Spin-Polarized Transport Studies

Michigan State University, East Lansing MI

Investigators

Abstract

Technical: This program involves two related projects with technological potential. Current-Perpendicular-to-Plane Magnetoresistance of metallic magnetic multilayers is a competitor for next generation read-heads for hard-disks. Comparing measured specific resistances (sample area times resistance) of interfaces between new pairs of carefully chosen metals, with no-free-parameter calculations made by collaborators, will let the MSU group test fundamental understanding of transport in multilayers, thus providing the basis for technological design. Spin-transfer-torque induced magnetization switching and generation of GHz radiation in magnetic multilayers is of interest for writing magnetic random access memory and as a current-controlled source of radiation. To clarify the underlying physics, the MSU group will measure how switching currents and radiation vary with different combinations of magnetic and non-magnetic metals. The group also plans to study generation of vortices in nanopillars and with point contacts (the latter a collaboration), including in multilayers with antiferromagnets. These projects will give graduate and undergraduate students experience in planning and carrying out cutting-edge research. The program involves international collaborations. Non-technical: This program involves two projects, both involving metallic magnetic multilayers, alternating layers of magnetic and non-magnetic metals, with each layer only a few atoms thick. The change in electrical resistance with applied magnetic field, measured with the current flowing perpendicular to the layer planes of the multilayer, is a competitor for next generation read-heads for computer hard-disks. The MSU group will compare measurements of specific resistances (sample area times resistance) of interfaces between carefully chosen pairs of metals, with no-free-parameter calculations by collaborators. This comparison will provide the basis for technological design. Until recently, the magnetizations of magnetic layers (effectively, tiny magnets) in magnetic nanopillars could be reversed (switched) only with an external magnetic field. However, it was predicted, and then shown, that a new phenomenon, spin-transfer-torque (STT), lets such switching be induced by passing a large enough current density through the nanopillar. Such current-induced switching is of interest for writing multilayer magnetic random access memory. STT also allows generation of high-frequency (giga-Hertz) electromagnetic radiation with the technologically interesting ability to change the frequency by varying the applied current. Studies of combinations of different magnetic and non-magnetic metals will clarify the physics underlying both phenomena, thereby assisting technological design. These projects give graduate and undergraduate students experience in planning and carrying out cutting-edge research.