title: First-order reorientation transition of the flux-line lattice in CaAlSi.
abstract: The flux-line lattice in CaAlSi has been studied by small-angle neutron scattering. A well-defined hexagonal flux-line lattice is seen just above H(c1) in an applied field of only 54 Oe. A 30° reorientation of this vortex lattice has been observed in a very low field of 200 Oe. This reorientation transition appears to be first-order and could be explained by nonlocal effects. The magnetic field dependence of the form factor is well-described by a single penetration depth of λ=1496(1) Å and a single coherence length of ξ=307(1) Å at 2 K. At 1.5 K, the penetration depth anisotropy is γ(λ)=2.7(1), with the field applied perpendicular to the c axis, and agrees with the coherence length anisotropy determined from critical field measurements.
authors.affiliation: Physics Department, University of Warwick, Coventry, United Kingdom. P.K.Biswas@warwick.ac.uk
authors.forename: P K
authors.initials: PK
authors.lastname: Biswas
authors.forename: M R
authors.initials: MR
authors.lastname: Lees
authors.forename: G
authors.initials: G
authors.lastname: Balakrishnan
authors.forename: D Q
authors.initials: DQ
authors.lastname: Liao
authors.forename: D S
authors.initials: DS
authors.lastname: Keeble
authors.forename: J L
authors.initials: JL
authors.lastname: Gavilano
authors.forename: N
authors.initials: N
authors.lastname: Egetenmeyer
authors.forename: C D
authors.initials: CD
authors.lastname: Dewhurst
authors.forename: D McK
authors.initials: DM
authors.lastname: Paul