The aggregation of ferrocolloids in a magnetic field

The structure of chain aggregates forming in a low-concentration monodisperse ferrocolloid in a uniform permanent magnetic field was studied. The configuration integral of a flexible fluctuating chain of arbitrary length was calculated using the matrix method of coordinate system rotation with allowance made for the dipole-dipole interaction of the magnetic moments of nearest ferroparticles. The equilibrium distribution over aggregate chain lengths was determined from the condition of minimum of the free energy functional. It was shown that, even for infinitely diluted ferrofluids, an increase in the strength of external magnetic field led to a noticeable lengthening of chain aggregates at strong interparticle magnetodipole interaction. This results in faster (compared to Langevin’s law) growth of the magnetization of a system in weak and intermediate fields.