Effects of DC magnetic field in the range of 0–180 mT on the properties of cobalt oxide nanoparticles (Co3O4 NPs) synthesized by pulse laser ablation method in distilled water has been investigated. Ablation was carried out in the presence of permanent magnets with variable strengths. Significant blue shift in excitonic absorption peaks of produced nanoparticles show that with increasing the magnetic field strength during the ablation process, size of nanoparticles was decreased noticeably. This result was confirmed by SEM and TEM images. XRD pattern show that with applying external magnetic field we may have crystalline structure nanoparticles while in the absence of external magnetic field, only amorphous phase of Co nanoparticles was produced. FTIR spectra present the metal oxygen vibration at 614 and 668 cm−1, revealed octahedral and tetrahedral site of cobalt oxide system. In overall it can be concluded that external magnetic field is a strong tool to control the properties of laser ablation produced ferromagnetic nanoparticles.
