Optical and magnetic properties of Fe nanoparticles fabricated by femtosecond laser ablation in organic and inorganic solvents

Abstract

Magnetic nanoparticles have attracted much interest due totheir broad applications in biomedicine and pollutant remediation.In this work, the optical, magnetic, and structural characteristicsof colloids produced by ultrashort pulsed laser ablationof a solid Fe target were studied in four different media:HPLC water, an aqueous solution of trisodium citrate, acetone,and ethanol. Optical extinction spectroscopy revealed an absorptionband in the UV region for all, in contrast to the resultsobtained with nanosecond lasers. Micro-Raman spectroscopyshowed that the samples are heterogeneous in their composition,with hematite, maghemite, and magnetite nanoparticlesin all four solvents. Similar results were obtained by electrondiffraction, which also found a-Fe. Magnetic properties werestudied by vibrating-sample magnetometry, and showed nanoparticlesin the superparamagnetic state. Under certain experimentalconditions, submicrometer-sized iron oxide nanoparticlesagglomerate into fractal patterns that show self-similarproperties. Self-assembled annular structures on the nanometerscale were also observed and are reported for the firsttime.