Neutron Scattering Study of the Flux Lattice in YNi2B2C

Abstract

We observe a flux lattice with square symmetry in the superconductor YNi{sub 2}B{sub 2}C when the applied field is parallel to the {ital c} axis of the crystal. A square lattice observed previously by Yaron {ital et al.} in the isostructural magnetic analog ErNi{sub 2}B{sub 2}C was attributed to the interaction between magnetism in that system and the flux lattice. Since the Y-based compound does not order magnetically, it is clear that the structure of the flux lattice is unrelated to magnetic order. We do not observe any change in the mosaic or direction of the flux lines with applied field; these phenomena may be related to magnetism. In YNi{sub 2}B{sub 2}C, the strength of the flux lattice signal was seen to fall off rapidly with applied field; the results imply considerable disorder in the arrangement of the flux lines at 2.5T, but are not consistent with melting. We see a markedly anisotropic flux lattice when the applied field is at 60{degree} to the {ital c} axis. In this case, the flux lattice is observed to be a distorted hexagon. {copyright} {ital 1997} {ital The American Physical Society}