Commensurate and incommensurate magnetic structures of UNiGe

Abstract

A single crystal of the orthorhombic intermetallic compound UNiGe has been studied at both steady-state and pulsed neutron sources in its commensurate (T41.5 K) and incommensurate (41.5T51 K) magnetic phases. The ordering wave vector in both phases is q=(0,\ensuremath{\delta},\ensuremath{\delta}), with \ensuremath{\delta}=1/2 in the commensurate phase. \ensuremath{\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 moment configurations in real space, and least-squares refinement gives a moment of 0.36${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ at 46 K, compared with 0.96${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ at 20 K. While symmetry allows moment components along all three Cartesian directions, previous unpolarized-neutron-diffraction data had been analyzed in terms of a collinear arrangement of moments in the b-c plane. Polarized neutron diffraction in the low-temperature commensurate phase shows that it is noncollinear, with an additional x component to the uranium moment, and there is some evidence that this is also the case in the incommensurate phase. The polarized-neutron measurement gives a canting angle, with respect to the b-c plane, of 17\ifmmode\pm\else\textpm\fi{}4\ifmmode^\circ\else\textdegree\fi{}. The observed ${\mathrm{\ensuremath{\mu}}}_{\mathit{x}}$ components are discussed in terms of bonding of the 5f-electron orbitals with the surrounding ligands. \textcopyright{} 1996 The American Physical Society.