Handling the particle size and distribution of Fe3O4 nanoparticles through ball milling

A series of samples consisting of spinel Fe₃O₄ nanoparticles with controlled particle sizes and increasing concentration has been obtained through ‘mild’ ball milling (BM) experiments by using an organic carrier liquid. We have succeeded in producing quite narrow particle size distributions with mean values d7–10 nm by an appropriate choice of the milling time for each concentration. The method proved to be practical to tailor the final particle size without formation of undesirable phases. All samples showed superparamagnetic behavior at room temperature, with transition to a blocked state at T_B10–20 K. The mean value and distribution width of the size distributions for the three samples studied were obtained from M(H) cycles recorded at T>T_B showing good agreement with X-ray diffraction and electron microscopy results. The effect of increasing interparticle interactions was to shift T_B upwards, as inferred from magnetization measurements. Mössbauer spectra at low temperatures showed no evidence of enhanced spin disorder.