Determination of Ferrofluid Structure by Neutron Polarization Analysis

Neutron polarization analysis is combined with small-angle scattering for the study of a concentrated cobalt ferrofluid. The geometry of the cobalt particle core and surrounding surfactant layer has been determined and an anomalous magnetic layer found at the cobalt surface. The interparticle structure factor, measured for the first time in a magnetically aligned ferrofluid, agrees well with a recent theory. Magnetic fluctuations, measured as a function of applied field, are found to be predominantly paramagnetic.