A mean field approach to analyze the magnetization of interacting ferrimagnetic particles under superparamagnetic conditions

Nanoparticles of magnetite are synthesized. A part of these particles are covered with oleic acid. Both, the bare and the covered, samples are characterized by x-ray diffractometry, transmission electron microscopy, Fourier transform infrared spectroscopy and magnetometry. Mean crystallite size of magnetite nanoparticles in both samples is 6.5 nm. These magnetic particles are seen to be superparamagnetic. The Langevin function is used to describe the magnetization of samples. But the mean particle magnetic moment can be overestimated by this approach. The Langevin function does not consider any dipolar interactions among particles. Concept of mean field theory is used in the Langevin function. This new function describes the magnetization of interacting particles well and results sensible values for the mean particles magnetic moment.