We investigate spin correlations in the dipolar Heisenberg antiferromagnet Gd2Sn2O7 using polarised neutron-scattering measurements in the correlated paramagnetic regime. Using Monte Carlo methods, we show that our data are sensitive to weak further-neighbour exchange interactions of magnitude ~0.5% of the nearest-neighbour interaction, and are compatible with either antiferromagnetic next-nearest neighbour interactions, or ferromagnetic third-neighbour interactions that connect spins across hexagonal loops. Calculations of the magnetic scattering intensity reveal rods of diffuse scattering along [111] reciprocal-space directions, which we explain in terms of strong antiferromagnetic correlations parallel to the set of <110> directions that connect a given spin with its nearest neighbours. Finally, we demonstrate that the spin correlations in Gd2Sn2O7 are highly anisotropic, and correlations parallel to third-neighbour separations are particularly sensitive to critical fluctuations associated with incipient long-range order.
@article{arxiv.1608.05062,
title = {Spin Correlations in the Dipolar Pyrochlore Antiferromagnet Gd2Sn2O7},
author = {Joseph A. M. Paddison and Georg Ehlers and Oleg A. Petrenko and Andrew R. Wildes and Jason S. Gardner and J. Ross Stewart},
journal= {arXiv preprint arXiv:1608.05062},
year = {2017}
}