Issue |
Europhys. Lett.
Volume 57, Number 1, January 2002
|
|
---|---|---|
Page(s) | 93 - 99 | |
Section | Condensed matter: electronic structure, electrical, magnetic, and optical properties | |
DOI | https://doi.org/10.1209/epl/i2002-00546-1 | |
Published online | 01 September 2002 |
Competition between exchange and anisotropy in a pyrochlore ferromagnet
1
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
Received:
9
March
2001
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 [001] 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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