Magnetic Structure of U2Ni2Sn*

Uranium intermetallics of the U₂T₂X (U = Uranium, T = transition metal, X = p-electron ligand) family, in general, contain magnetic moments perpendicular to the shortest U-U distance within the crystal structure. U₂Ni₂Sn, belonging to this family, crystallizes in the tetragonal Mo₂FeB₂ structure and has the shortest U-U distance along the basal plane. It orders antiferromagnetically at 26 K with the propagation vector q = (0, 0, 1/2). Previous neutron powder diffraction studies of this compound, albeit somewhat ambiguous, reported U magnetic moments aligned in the basal plane. This result represents an exception to the established trend about orientation of uranium moments in this family of compounds. However, new measurements on high-quality single crystals grown using Czochralski method have raised questions on the direction of the magnetic moment. We will present our single crystal neutron diffraction results on high quality single crystal to resolve the direction of the uranium magnetic moments. Our experiments show that the uranium moments align along the c-axis with a moment ≈ 0.85μ_B per U-atom at 5 K and help us resolve a long-standing ambiguity and understand better the magnetic anisotropy in these compounds.