Neutron Scattering Study of the Crystal and Magnetic Structures in Itinerant-5f Antiferromagnets UNiGa5 and UPtGa5

The crystal and magnetic structures of 5f itinerant antiferromagnets UNiGa5 and UPtGa5 were studied by means of neutron scattering. The powder diffraction data were well explained by the HoCoGa5 tetragonal structure: with space group P4/mmm. In UNiGa5, uranium spins in the simple tetragonal lattice have a Neel-type structure with a relatively large moment of 0.9 mu(B)/U along the [0,0,1] direction. On the other hand, magnetic moments of uranium atoms in UPtGa5 are aligned ferromagnetically in the (0,0,1) plane and are directed along the [0,0,1] direction in an antiferromagnetic sequence (up arrowdown arrow). An ordered moment is 0.24 mu(B)/U. The nearest-neighbor interaction might be different in these isostructural compounds.