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 URu2Si2 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 µB /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 Smax ‖ ≤ 1·10−3 µB /U