Optical, magnetic and thermal properties of colloidal suspension of ferrofluids synthesized by laser ablation

A high power Nd:YAG laser has been employed to produce magnetic colloids (ferrofluids) of iron oxide nanoparticles (NPs) in double distilled water. It is found that FeO (Wusite) phase of iron oxide has been produced as an initial product; after oxidation and agglomeration it appears as Fe2O3 a stable composition of iron oxide. UV-visible absorption spectroscopy has been employed to distinguish both phases of iron oxide NPs. Absorption band gap of as synthesized ferrofluids at different pulse energies (30, 40, 50, 60 mJ) has been calculated. The absorption band gap of as synthesized FeO magnetic colloids is found in the range of (2.91-3.13 eV) and (3.37-3.91 eV) respectively which arises due to pair excitation and charge transfer. Absorption band gaps of Fe2O3 are found in the range of (2.16-2.28 eV) and (2.68-3.10 eV) respectively again due to pair excitation and charge transfer. Magnetic measurement was performed using VSM which confirms antiferromagnetic nature of FeO NPs with coercivity 47 Oe and magnetic domain size 73.50 angstrom at 300 K. Zero field cooled and field cooled magnetization confirms blocking and Neel temperature 245 +/- 2 K and 181 +/- 2 K respectively.