Electronic topological transitions, magnetic ordering and the Fermi surfaces of and the heavy rare earths

¹ H. H. Wills Physics Laboratory, University of Bristol Tyndall Avenue, Bristol, BS8 1TL, UK
² Department of Physics, University of Warwick - Coventry, CV4 7AL, UK

Received: 8 August 2003
Accepted: 12 November 2003

Abstract

The magnetic order of the heavy rare earths has long been associated with the presence of a certain feature in the Fermi surface (FS) topology (being common to non-magnetic also), known as the “webbing”. Furthermore, there has been speculation that changes in the observed ordering, brought about by temperature-induced changes in the crystalline ratio, are due to the presence or absence of that webbing feature. Such a simplistic model is appealingly simple in systems where physics of the exchange interaction as a function of composition and temperature is complicated. The _x alloy system exhibits ferromagnetism or helical antiferromagnetism at different compositions and temperatures. We present our experimental measurement of the FS topology of such an alloy at a composition close to the concentration where helical antiferromagnetism occurs. The data show that the evolution of the FS in _x is different from that predicted by the model based on the ratio, suggesting a less simplistic interpretation.