Neutron Scattering Study of the Crystal and Magnetic Structures in Itinerant-5f Antiferromagnets UNiGa_5 and UPtGa_5

摘要

The crystal and magnetic structures of 5f itinerant antiferromagnets UNiGa_5 and UPtGa_5 were studied by means of neutron scattering. The powder diffraction data were well explained by the HoCoGa_5 tetragonal structure with space group P4/mmm. In UNiGa_5, uranium spins in the simple tetragonal lattice have a Neel-type structure with a relatively large moment of 0.9 μ_B/U along the [0,0,1] direction. On the other hand, magnetic moments of uranium atoms in UPtGa_5 are aligned ferromagnetically in the (0,0,1) plane and are directed along the [0,0,1] direction in an antiferromagnetic sequence (↑↓). An ordered moment is 0.24μ_B/U. The nearest-neighbor interaction might be different in these isostructural compounds.