Abstract :
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 〈d〉∼7–10 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 TB∼10–20 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>TB showing good agreement with X-ray diffraction and electron microscopy results. The effect of increasing interparticle interactions was to shift TB upwards, as inferred from magnetization measurements. Mössbauer spectra at low temperatures showed no evidence of enhanced spin disorder.
