Reflectivity and off-specular neutron scattering from the free ferrofluid surface and silicon-ferrofluid interface

Properties of the free ferrofluid (colloid of fine magnetite particles suspended in heavy water) surface and interface silicon-ferrofluid is studied by means of the neutron reflectivity and off-specular scattering. The measurements were performed in zero magnetic field, as well as in the presence of the field, applied within the surface (interface) plane, either perpendicular or parallel to the incoming beam. Proposed theoretical model allows deriving quantitative information about ferrofluid structure from the data of the interface measurements while consideration of the free surface data requires some additional contemplation. The experimental results collected, mainly in maps initial angle - scattered angle, were treated by means of two-dimensional fit (the least-squares routine) and values of the ferrofluid parameters such as correlation radius, critical angle, scattering length density were obtained ill dependence on value and direction of external magnetic field. The capability of polarized neutron reflection experiment for the investigation of the magnetization process in the vicinity of the ferrofluid free surface (interface) is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.