Professor John Gregg

Abstract:

This review is intended as an introduction to mesomagnetism, with an emphasis on what the defining length scales and their origins are. It includes a brief introduction to the mathematics of domains and domain walls before examining the domain patterns and their stability in 1D and 2D confined magnetic structures. This is followed by an investigation of the effects of size and temperature on confined magnetic structures. Then, the relationship between mesomagnetism and the developing field of spin electronics is discussed. In particular, the various types of magnetoresistance, with an emphasis on the theory and applications of giant magnetoresistance and tunneling magnetoresistance, are studied. Single electronics are briefly examined before concluding with an outlook on future developments in mesomagnetism.

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.