Professor John Gregg

Abstract:

A mechanism is described which considers the effect of small magnetic particles on the spin diffusion length in a granular giant magnetoresistive material. Spin depolarization occurs by precession of the spin orientation of the carrier due to the s-d exchange interaction within a magnetic particle. Numerical simulation of this jitterbug effect is found to generate a temperature and field dependence of the distance a carrier may travel within the sample without losing its spin memory. (C) 1996 American Institute of Physics.

Abstract:

Co-Ag granular films are prepared by molecular-beam epitaxy to enable a detailed structural study to be conducted in conjunction with magnetotransport properties. It is demonstrated that the shape, size, location, and segregation of the magnetic Co grains and the morphology of the surface depend on the growth temperature. Detailed transmission electron microscopy reveals inherent differences between samples prepared at room temperature and those prepared at high temperature. Small clusters of only a few atoms are found to be present in the matrix of the low-temperature samples significantly affecting the spin diffusion length. Well-crystallized regions of both Co and Ag are found in the high-temperature samples, however, the Co grains remain relatively small in size even at the highest growth temperatures. (C) 1996 American Institute of Physics.

Abstract:

Giant magnetoresistive Co-Ag granular films are prepared by molecular beam epitaxy at three different temperatures with cobalt concentrations ranging from 30 to 80 at. %. The structural properties of these films are studied using a variety of diffraction techniques and real space probes. Magnetization and magnetotransport measurements are carried out at room temperature. Correlating the structural and magnetotransport properties reveals that the spin diffusion length strongly affects the amplitude of the giant magnetoresistance, which is otherwise dominated by the surface-to-volume ratio of the segregated magnetic precipitates. © 1996 The American Physical Society.