COMMENSURATE AND INCOMMENSURATE MAGNETIC-STRUCTURES OF UNIGE

A single crystal of the orthorhombic intermetallic compound UNiGe has been studied at both steady-state and pulsed neutron sources in its co mmensurate (T<41.5 K) and incommensurate (41.5<T<51 K) magnetic phases . The ordering wave vector in both phases is q=(0,delta,delta), with d elta=1/2 in the commensurate phase. delta is temperature dependent in the incommensurate phase, increasing from 0.35 at 50 K to 0.37 at 44 K . Irreducible representation theory is used to discuss the possible mo ment configurations in real space, and least-squares refinement gives a moment of 0.36 mu(B) at 46 K, compared with 0.96 mu(B) at 20 K. Whil e symmetry allows moment components along all three Cartesian directio ns, previous unpolarized-neutron-diffraction data had been analyzed in terms of a collinear arrangement of moments in the b-c plane. Polariz ed neutron diffraction in the low-temperature commensurate phase shows that it is noncollinear; with an additional x component to the uraniu m moment, and there is some evidence that this is also the case in the incommensurate phase. The polarized-neutron measurement gives a canti ng angle, with respect to the b-c plane, of 17+/-4 degrees. The observ ed mu(x) components are discussed in terms of bonding of the Sf-electr on orbitals with the surrounding ligands.