Hybridization effects in U2T2X compounds: Magnetic structures of U2Rh2Sn and U2Ni2In

The tetragonal intermetallic compounds ${\mathrm{U}}_{2}$${\mathrm{Ni}}_{2}$In and ${\mathrm{U}}_{2}$${\mathrm{Rh}}_{2}$Sn have been studied by means of specific-heat, electrical-resistivity, and neutron-diffraction techniques. At low temperatures, both compounds order antiferromagnetically in a magnetic unit cell doubled along the c axis, and we find 5f moments of 0.60 and 0.38${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$/U atom for ${\mathrm{U}}_{2}$${\mathrm{Ni}}_{2}$In and ${\mathrm{U}}_{2}$${\mathrm{Rh}}_{2}$Sn, respectively. For ${\mathrm{U}}_{2}$${\mathrm{Ni}}_{2}$In, our refinement also indicates a possible Ni moment of 0.37${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ perpendicular to the U moments. We discuss the development of the 5f moments together with findings on other isostructural ${\mathrm{U}}_{2}$${\mathit{T}}_{2}$X (T=transition metal, X=In, Sn) compounds, and confirm that the trends expected due to 5f-ligand hybridization also hold for this family of uranium compounds. Our analysis indicates different arrangements of the 5f moments in the two compounds (noncollinear arrangement within the basal plane for ${\mathrm{U}}_{2}$${\mathrm{Ni}}_{2}$In and collinear arrangement along the c axis for ${\mathrm{U}}_{2}$${\mathrm{Rh}}_{2}$Sn), although both compounds have nearest-neighbor U-U distances along the c axis. This would mean that the magnetocrystalline anisotropy in ${\mathrm{U}}_{2}$${\mathit{T}}_{2}$X compounds is not determined by nearest-neighbor U-U links alone. \textcopyright{} 1996 The American Physical Society.