Professor John Gregg

Abstract:

The magnetoresistance (MR) of a nickel atomic contact has been measured using the break junction technique. When the contact is only between two atoms, the change of resistance with applied field reaches 40%. It is composed of a continuous bell-shaped curve on which discrete jumps are superimposed. The MR changes sign when the applied field is rotated, which we explain by a spin-orbit coupling change of orbital overlap between the Ni atoms forming the junction. Reproducible jumps in the MR curve are attributed to a field induced change of spin configuration within the few atoms composing the contact.

Abstract:

One of the most critical steps in the realization of high quality tunneling devices is the fabrication of ultrathin oxide layers. This article describes a powerful technique for controlling the oxidation of ultrathin metallic layers. The technique consists of depositing the metallic layer to be oxidized on top of the soft magnetic layer of a bottom spin valve. The oxidation kinetics are then monitored by measuring the current in plane sheet resistance and magnetoresistance. The technique relies on the extreme sensitivity of the magnetoresistance on the degree of specular reflection at the soft magnetic layer/oxide interface. (C) 2002 American Institute of Physics.

Abstract:

We propose a simple method to make metallic nanocontacts. A gap is electrochemically etched in a Ni track. The gap resistance is monitored as material is redeposited from the solution to bridge the gap. I:V characteristics were compared with those of Ni nanocontacts fabricated using a focussed ion beam (FIB). The I:V characteristic is asymmetric above 200 K in both cases. (C) 2002 Published by Elsevier Science B.V.

Abstract:

The ultra-thin oxide tunnel barrier employed in magnetic tunnel junctions stack has to be of very high quality in terms of large scale homogeneity of its thickness and height parameters. For controlling precisely oxidation kinetic, we used spin valves as an oxidation progress probe. By measuring the magnetoresistance effect versus the oxidation time we are able to detect under- or over-oxidation of the metallic material. This technique consists of analysing the ability of spin-dependent electron scattering at metal/oxide interfaces. (C) 2002 Elsevier Science B.V. All rights reserved.