Volume 57, Number 1, January 2002
|Page(s)||93 - 99|
|Section||Condensed matter: electronic structure, electrical, magnetic, and optical properties|
|Published online||01 September 2002|
Competition between exchange and anisotropy in a pyrochlore ferromagnet
University College London, Department of Chemistry
20 Gordon Street, London WC1H0AJ, UK
2 Laboratoire de Physique, Ecole Normale Supérieure 46 Allée d'Italie, F-69634 Lyon cedex 07, France
3 ISIS Facility, Rutherford Appleton Laboratory Chilton, Didcot, Oxon OX11 0QX, UK
Accepted: 19 October 2001
The Ising-like spin ice model, with a macroscopically degenerate ground state, has been shown to be approximated by several real materials. Here we investigate a model related to spin ice, in which the Ising spins are replaced by classical Heisenberg spins. These populate a cubic pyrochlore lattice and are coupled to nearest neighbours by a ferromagnetic exchange term J and to the local axes by a single-ion anisotropy term D. The near-neighbour spin ice model corresponds to the case . For finite D/J we find that the macroscopic degeneracy of spin ice is broken and the ground state is magnetically ordered into a four-sublattice structure. The transition to this state is first order for D/J > 5 and second order for D/J < 5 with the two regions separated by a tricritical point. We investigate the magnetic phase diagram with an applied field along  and show that it can be considered analogous to that of a ferroelectric.
PACS: 75.10.Hk – Classical spin models / 75.40.Mg – Numerical simulation studies / 75.30.Kz – Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.)
© EDP Sciences, 2002
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