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Competition Between Exchange and Anisotropy in a Pyrochlore Ferromagnet

J. D. M. Champion·S. T. Bramwell·P. C. W. Holdsworth·M. J. Harris
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Abstract

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 <1,1,1> axes by a single-ion anisotropy term D. The near neighbour spin ice model corresponds to the case D/J infinite. 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 [1,0,0] and show that it can be considered analogous to that of a ferroelectric.

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J. D. M. Champion, S. T. Bramwell, P. C. W. Holdsworth, M. J. Harris. 2001-03-02. Competition Between Exchange and Anisotropy in a Pyrochlore Ferromagnet. https://doi.org/10.1209/epl%2Fi2002-00546-1

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