Professor John Gregg

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.

Abstract:

This review deals with practical aspects of making frequency-domain measurements of magnetic susceptibility and magnetic losses from 200 kHz up to 10 GHz. It sets out the types of measurement concerned, distinguishing resonant from nonresonant phenomena. The techniques available are categorized according to suitability for the different frequency regimes and types of investigation. Practical recipes are provided for undertaking such experiments across the entire frequency range. Marginal oscillator spectrometry is discussed which is applicable across the whole frequency range. Different instruments are presented, and particular emphasis is placed on designs which function on the Robinson principle. Analysis of oscillation condition and signal-to-noise performance is dealt with, also sample considerations such as filling factor. Practical circuits are presented and their merits and demerits evaluated. Layout and radio-frequency design considerations are dealt with. Ultrahigh/microwave frequency marginal oscillator spectrometry is given special treatment and several practical designs are given. The essentials of good microwave design are emphasized. A general discussion of resonant structures is included which treats multiple layer coil design, slow wave line structures, stripline and cavities. Unusual cavity designs such as the rhumbatron are treated. Use of striplines with microwave marginal spectrometry is described and compared with conventional network-analysis techniques. The use of parameter matrices for high-frequency analysis is alluded to. Some details of good construction practice are given together with some practical considerations relating to skin depth and other high-frequency phenomena.