Canonical examples of highly frustrated antiferromagnets are the gadolimium pyrochlores Gd2Ti2O7 (GTO) and Gd2Sn2O7 (GSO) both of which order at ~1 K with different structures. GSO forms the Palmer-Chalker structure with a k = 0 propagation vector while GTO is reported to form a more complicated - and still controversial - partially ordered state with a propagation vector of k=(1/2, 1/2, 1/2), splitting the crystallographically equivalent Gd sites into non-equivalent magnetic sites [1]. Standard neutron diffraction techniques don't allow unambiguous determination of the k-state, (i.e. 1 or a combination of the 4 possible propagation vectors). However, using a combination of single crystal diffraction, diffuse and inelastic neutron scattering on both powder and single crystal samples of GTO, we have determined that the partially ordered magnetic structure is double-k with orthorhombic space group symmetry. This is in agreement with recent theoretical predictions of a double-k structure based on mean-field-theory with thermal fluctuations [2]
1. Stewart, J. R., et al., J. Phys. Condens. Matter 16, L321-L326 (2004).
2. Javanparast, B. et al., Physical Review Letters, 114 130601 (2015)