Determining the size distribution of magnetic nanoparticles based on analysis of magnetization curves

This study develops a direct scheme that is based on the magnetization curve of magnetic nanoparticles in the medium-field region above the blocking temperature to extract information on the size of particles and the uniformity thereof. The magnetization curve was fitted with a computer software that was developed in-house and based on the linear addition of the Langevin functions that correspond to particles of different sizes. Numerically generated curves demonstrate that a standard deviation in volume of 10% generates a variation in magnetization of approximately 1%. The fitting program was tested on a series of generated curves for magnetic nanoparticles with various average volumes and standard deviations, yielding results with errors of around 3%. The program was also justified using the data obtained from several published articles, and the results herein were found to agree closely with those in the articles. Magnetite nanoparticles were monodispersed in a polymer matrix and magnetic measurements were made. The obtained results were compared with transmission electron microscopy observations to further validate the developed scheme. (C) 2009 American Institute of Physics. [doi:10.1063/1.3259424]