Colloquia 2005

Ferromagnets ain't ferromagnets: polarized neutron scattering and the search for non-collinear ferromagnetism

Dr. Andrew Wildes,
Institut Laue-Langevin, Grenoble, France

Date

4-5 p.m., Thursday, 3 November, 2005 .

Location

School of Physics Common Room
Room 64 Old Main Building
The University of New South Wales

Abstract
Ferromagnets are normally defined as magnetic materials where all the atomic moments are collinear and parallel. It is, however, becoming more and more common to explain the properties of many ferromagnetic materials in terms of non-collinear magnetism, where an atomic magnetic moment might have a component perpendicular to the mean ferromagnetic direction. Bulk effects such as non-saturation of the magnetization, magnetic softness, and zero thermal expansion (the INVAR effect) have all been attributed to non-collinear ferromagnetism in recent years, and, aided by advances in computer speed, ab-initio calculations involving large numbers of atoms confirm that these structures might exist.

Experimental techniques capable of measuring non-collinear ferromagnetism are few, however. Of these, the only technique capable of measuring spatial correlations between the non-collinear components is neutron scattering with polarization analysis. Since the late 1980s, a collaboration between the universities of Oxford and Sheffield and the Institute Laue-Langevin has focused on using this technique to search for non-collinear ferromagnetism in a range of systems, predominantly iron-based metallic glasses. This presentation will summarise the major findings of the collaboration to date, and, while premature, will attempt to put forward the beginnings of a global picture.

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