Photoacoustic spectroscopy of magnetic fluids

Abstract In this study photoacoustic spectroscopy is introduced as a promising experimental technique to investigate magnetic fluids (MFs). The spectral features of representative uncoated- and coated MFs in the 0.3–1.0 μm wavelength region have been discussed and identified in terms of three distinct bands (L, S, and C). Band-L in the spectral range 0.65–0.90 μm was ascribed to the characteristic coating layer of the magnetic nanoparticle. Band-S occurring around 0.47 μm was ascribed to the metal-poly oxy-hydroxy surface layer built up at the nanoparticle surface. Finally, band-C has been associated to the optical band edge absorption of the semiconductor magnetic nanoparticle. Fe 3 O 4 nanoparticles (9.4 nm diameter) and CoFe 2 O 4 nanoparticles (4.3 and 11.4 nm diameter) were used as core materials in the coated- and uncoated-MF samples, respectively.