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 degrees 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 lambda = 1496(1) angstrom A and a single coherence length of xi = 307(1) angstrom at 2 K. At 1.5 K, the penetration depth anisotropy is gamma(lambda) = 2.7(1), with the field applied perpendicular to the c axis, and agrees with the coherence length anisotropy determined from critical field measurements.