New Journal of Physics (Jan 2013)
Absence of a static in-plane magnetic moment in the ‘hidden-order’ phase of URu2Si2
Abstract
We have carried out a careful magnetic neutron scattering study of the heavy fermion compound URu _2 Si _2 to probe the possible existence of a small magnetic moment parallel to tetragonal basal plane in the ‘hidden-order’ phase. This small in-plane component of the magnetic moment on the uranium sites S _∥ has been postulated by two recent models (rank-5 superspin/hastatic order) aiming to explain the hidden-order phase, in addition to the well-known out-of-plane component S _⊥ ≈ 0.01–0.04 μ _B /U. In order to separate S _∥ and S _⊥ , we take advantage of the condition that for magnetic neutron scattering only the components of the magnetic structure that are perpendicular to the scattering vector Q contribute to the magnetic scattering. We find no evidence for an in-plane magnetic moment S _∥ . Based on the statistics of our measurement, we establish that the upper experimental limit for the size of any possible in-plane component is S ^max _∥ ⩽ 1 × 10 ^−3 μ _B /U.