Power-law spin correlations in pyrochlore antiferromagnets

The ground state ensemble of the highly frustrated pyrochlore-lattice antiferromagnet can be mapped to a coarse-grained “polarization” field satisfying a zero-divergence condition. From this it follows that the correlations of this field, as well as the actual spin correlations, decay with separation like a dipole-dipole interaction $(1∕\mid R{\mid }^3)$. Furthermore, a lattice version of the derivation gives an approximate formula for spin correlations, with several features that agree well with simulations and neutron-diffraction measurements of diffuse scattering, in particular the pinch-point (pseudo-dipolar) singularities at reciprocal lattice vectors. This system is compared to others in which constraints also imply diffraction singularities, and other possible applications of the coarse-grained polarization are discussed.

Figure 1

(Color online) (a) Ising ground state on fragment of pyrochlore lattice; spins are shown on edges of a diamond lattice. (b). The corrsponding ice-model arrows between the diamond vertices.

Figure 2

Calculated structure factor in the plane normal to $\left[1\overline{1}0\right]$. (The figure is the same slice as shown in Refs. 44, 51.)