Professor John Gregg

Abstract:

Spin injection into and spin transport through silicon spacer layers in iron/silicon/cobalt structures has been investigated. Ultrahigh vacuum evaporated silicon spacers of varying crystal quality from amorphous to epitaxial of thicknesses from 10 to 200 Angstrom were shown to improve their electrical conduction with increasing crystallinity, but no spin dependent transport was observed through the structure. Silicon and iron interdiffusion was also observed at the interfacial region. Device quality silicon was studied using 460 and 540 mu m doped silicon wafers of resistivity 0.1 and 1 Omega cm, respectively, polished on both sides, onto which were deposited iron and cobalt layers. Sharp metal-semiconductor interfaces were achieved in this way, but no spin dependent transport, putting an upper limit on the spin diffusion length in device quality silicon wafers. (C) 2000 American Institute of Physics. [S0021-8979(00)92808-1].

Abstract:

The intermetallic compound CeCo3 has been irradiated at GANIL by 1 GeV Pb-208 ion beams. The irradiated samples are found to be strongly amorphised. A track diameter of 8 nm is found. The magnetic properties of the irradiation induced CeCo3 amorphous phase have been studied in detail and found substantially different with respect to those of amorphous CeCo3 obtained by conventional methods. In particular, an increase of about 200 K in the Curie temperature is observed, suggesting that a different type of chemical short range order might have been stabilized by irradiation. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

We present magnetisation and giant magnetoresistance (GMR) measurements for MBE grown CoAg granular films with the external field applied parallel and perpendicular to the film plane. Both the magnetisation and the GMR show uniaxial anisotropy with the easy axis of magnetisation out-of-plane for Co concentrations of 30 at% and less and in the film plane for higher Co concentrations. We attribute this behaviour to the shape anisotropy of the magnetic particles in the films.