Initial magnetic susceptibility of ferrocolloids: The influence of chain aggregates

The behavior of a system of noninteracting chain aggregates of ferroparticles suspended in a liquid matrix and subjected to a weak uniform permanent magnetic field was studied based on the free energy functional of a monodisperse low-concentration magnetic colloid. The orientational response of a flexible chain to a weak external field showed that the model of rigid rods is applicable only for short chains (doublets and triplets) of large ferroparticles characterized by a strong magnetodipole interaction. The calculated values of the initial magnetic susceptibility of aggregated ferrofluid agree well with the computer simulation data.