Raman study of ionic water-based copper and zinc ferrite magnetic #uids

Abstract Raman spectroscopy is used to investigate the OH-bending and OH-stretching modes of chemisorbed OH-groups in copper-ferrite and zinc-ferrite water-based magnetic #uid samples. Room-temperature Raman spectra were taken from diluted magnetic #uid samples and compared with the spectrum taken from liquid water. The suppression of the symmetric OH-stretching Raman modes from the ionic magnetic #uid sample spectra is discussed in terms of the replacement of a hydrogen atom from the water molecule by the nanoparticle surface. Moreover, changes on the area ratio between hydrogen bonded and nonhydrogen bonded OH-Raman peaks in the ionic magnetic #uid samples, as compared to the OH-Raman peaks from liquid water, are discussed in terms of changes on the hydrogen bond strength. 1999 Elsevier Science B.V. All rights reserved. Keywords: Raman spectroscopy; Magnetic #uids; Hydrogen bond; Chemisorption Magnetic #uids are ultra-stable colloidal systems consisting of monodomain magnetic nanoparticles dispersed in organic or inorganic liquid carrier. The stability of magnetic #uids is achieved through the balance between opposite particle interaction tendencies. From one side, particle thermal motion and particle}particle repulsion work together to keep particles apart. From the other side, Van der Waals and magnetic dipole interaction tend to stick particles together. Di!erent repulsion mechanisms are used to prevent particle}particle clustering, thus responding for di!erent types of magnetic * Corresponding author. Fax: #55-61-2723151. E-mail address: pcmor@"s.unb.br (P.C. Morais) #uids. Steric repulsion prevents agglomeration in surfacted magnetic #uids, whereas coulombic repulsion accounts for stability in ionic magnetic #uids [1]. High resolution microscopy, X-ray diffraction, magnetization measurements and optical birefringence measurements are the magnetic #uid standard characterization technique