title: Spin correlations in the dipolar pyrochlore antiferromagnet Gd2Sn2O7.
abstract: We investigate spin correlations in the dipolar Heisenberg antiferromagnet Gd2Sn2O7using 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 [1 1 1] reciprocal-space directions, which we explain in terms of strong antiferromagnetic correlations parallel to the set of [Formula: see text] directions that connect a given spin with its nearest neighbours. Finally, we demonstrate that the spin correlations in Gd2Sn2O7are highly anisotropic, and correlations parallel to third-neighbour separations are particularly sensitive to critical fluctuations associated with incipient long-range order.
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, United States of America. Churchill College, University of Cambridge, Storey's Way, Cambridge CB3 0DS, United Kingdom.
authors.forename: Joseph A M
authors.initials: JA
authors.lastname: Paddison
authors.forename: Georg
authors.initials: G
authors.lastname: Ehlers
authors.forename: Oleg A
authors.initials: OA
authors.lastname: Petrenko
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Wildes
authors.forename: Jason S
authors.initials: JS
authors.lastname: Gardner
authors.forename: J
authors.initials: J
authors.lastname: Ross Stewart