We present a study of magnetic and structural properties of CoFe2O4 nanoparticles suspended in an organic liquid. Transmission electron microscopy shows that the nanoparticles have a narrow size distribution of average particle size 5.9 ± 1.0？nm. X-ray diffraction shows that the particles are of cubic spinel crystal structure. Dynamic light scattering measurements reveal the existence of an organic shell around the CoFe2O4 nanoparticles with an average hydrodynamic diameter of 14.4？nm. Coercive magnetic field at ？K is found to be 11.8？kOe. Disappearance of the coercive field and remanent magnetization at about 170？K suggests that the CoFe2O4 nanoparticles are superparamagnetic at higher temperatures which is confirmed by the room temperature M？ssbauer spectrum analysis. Saturation magnetization of the nanoparticles of 80.8？emu/g(CoFe2O4) at 5？K reaches the value detected in the bulk material and remains very high also at room temperature. The cobalt ferrite nanoparticle system synthesized in this work exhibits magnetic properties which are very suitable for various biomedical applications. 1. Introduction Ferrofluids are stable colloidal suspensions of single domain magnetic particles in a carrier liquid. Stability of the magnetic colloid depends on the thermal contribution and on the balance between attractive and repulsive interactions. Magnetic dipole and van der Waals interactions have tendency to agglomerate the particles. In order to prevent agglomeration, the magnetic particles should be small enough (usually about 10？nm in size) and coated with a shell of an appropriate material. This coating can be a sufactant made of long chained molecules or ionic if it is an electric shell [1–3]. The particles are usually made of maghemite γ-Fe2O3, magnetite Fe3O4, and other ferrites of the type MFe2O4, where M = Mn, Co, Ni, Cu. The carrier liquid is usually an organic solvent or water. Ferrofluids respond to an external magnetic field. This enables the ferrofluid’s location to be controlled through the application of a magnetic field. Ferrofluids have a wide range of applications. They can be used to improve the performance of loud speakers [2]. Ferrofluids are also used in high-speed computer disk drives to eliminate harmful dust particles or other impurities that can cause the data-reading heads to crash into the disks. In recent years, a lot of research work has been devoted to biomedical applications of ferrofluids. In magnetic resonance imaging (MRI), ferrofluids are used as contrast agents [3–5]. Ferrofluids specially designed can carry drugs to
References
[1]
S. Odenbach, “Magnetic fluids—suspensions of magnetic dipoles and their magnetic control,” Journal of Physics Condensed Matter, vol. 15, no. 15, pp. S1497–S1508, 2003.
[2]
S. Odenbach, “Recent progress in magnetic fluid research,” Journal of Physics Condensed Matter, vol. 16, no. 32, pp. R1135–R1150, 2004.
[3]
C. Scherer and A. M. Figueiredo Neto, “Ferrofluids: properties and applications,” Brazilian Journal of Physics, vol. 35, no. 3, pp. 718–727, 2005.
[4]
C. C. Berry, “Progress in functionalization of magnetic nanoparticles for applications in biomedicine,” Journal of Physics D, vol. 42, no. 22, Article ID 224003, 9 pages, 2009.
[5]
H. Tan, J. M. Xue, B. Shuter, X. Li, and J. Wang, “Synthesis of PEOlated Fe3O4@SiO2 nanoparticles via bioinspired silification for magnetic resonance imaging,” Advanced Functional Materials, vol. 20, no. 5, pp. 722–731, 2010.
[6]
R. Rahisuddin, P. K. Sharma, M. Salim, and G. Garg, “Application of ferrofluid: as a targeted drug delivery system in nanotechnology,” International Journal of Pharmaceutical Sciences Review and Research, vol. 5, no. 3, pp. 115–119, 2010.
[7]
R. Skomski and J. M. D. Coey, Permanent Magetism, Institute of Physics Publishing, Bristol, UK, 1999.
[8]
M. Walker, P. I. Mayo, K. O'Grady, S. W. Charles, and R. W. Chantrell, “The magnetic properties of single-domain particles with cubic anisotropy. I. Hysteresis loops,” Journal of Physics, vol. 5, no. 17, pp. 2779–2792, 1993.
[9]
E. Blums, A. Cebers, and M. M. Maiorov, Magnetic Fluids, Walter de Gruyter, Berlin, Germany, 1997.
[10]
T. Jonsson, J. Mattsson, C. Djurberg, F. A. Khan, P. Nordblad, and P. Svedlindh, “Aging in a magnetic particle system,” Physical Review Letters, vol. 75, no. 22, pp. 4138–4141, 1995.
[11]
J. Zhang, C. Boyd, and W. Luo, “Two mechanisms and a scaling relation for dynamics in ferrofluids,” Physical Review Letters, vol. 77, no. 2, pp. 390–393, 1996.
[12]
A. Skumiel, A. Józefczak, T. Hornowski, and M. Labowski, “The influence of the concentration of ferroparticles in a ferrofluid on its magnetic and acoustic properties,” Journal of Physics D, vol. 36, no. 24, pp. 3120–3124, 2003.
[13]
M. Blanco-Mantecón and K. O'Grady, “Interaction and size effects in magnetic nanoparticles,” Journal of Magnetism and Magnetic Materials, vol. 296, no. 2, pp. 124–133, 2006.
[14]
L.-Y. Zhang, Y.-H. Dou, L. Zhang, and H.-C. Gu, “Magnetic behaviour and heating effect of Fe3O4 ferrofluids composed of monodisperse nanoparticles,” Chinese Physics Letters, vol. 24, no. 2, pp. 483–486, 2007.
[15]
M. B. Morales, M. H. Phan, S. Pal, N. A. Frey, and H. Srikanth, “Particle blocking and carrier fluid freezing effects on the magnetic properties of Fe3O4 -based ferrofluids,” Journal of Applied Physics, vol. 105, no. 7, Article ID 07B511, 3 pages, 2009.
[16]
G. Baldi, D. Bonacchi, C. Innocenti, G. Lorenzi, and C. Sangregorio, “Cobalt ferrite nanoparticles: the control of the particle size and surface state and their effects on magnetic properties,” Journal of Magnetism and Magnetic Materials, vol. 311, no. 1, pp. 10–16, 2007.
[17]
G. Baldi, D. Bonacchi, M. C. Franchini et al., “Synthesis and coating of cobalt ferrite nanoparticles: a first step toward the obtainment of new magnetic nanocarriers,” Langmuir, vol. 23, no. 7, pp. 4026–4028, 2007.
[18]
G. Baldi, G. Lorenzi, and C. Ravagli, “Hyperthermic effect of magnetic nanoparticles under electromagnetic field,” Processing and Applications of Ceramics, vol. 3, no. 1-2, pp. 103–109, 2009.
[19]
M. C. Franchini, G. Baldi, D. Bonacchi et al., “Bovine serum albumin-based magnetic nanocarrier for MRI diagnosis and hyperthermic therapy: a potential theranostic approach against cancer,” Small, vol. 6, no. 3, pp. 366–370, 2010.
[20]
V. Cabuil, V. Dupuis, D. Talbot, and S. Neveu, “Ionic magnetic fluid based on cobalt ferrite nanoparticles: influence of hydrothermal treatment on the nanoparticle size,” Journal of Magnetism and Magnetic Materials, vol. 323, no. 10, pp. 1238–1241, 2011.
[21]
H. Guo, X. Yang, T. Xiao, W. Zhang, L. Lou, and J. Mugnier, “Structure and optical properties of sol-gel derived Gd2O3 waveguide films,” Applied Surface Science, vol. 230, no. 1–4, pp. 215–221, 2004.
[22]
H. Shenker, “Magnetic anisotropy of cobalt ferrite (Co1.01Fe2.00O3.62) and nickel cobalt ferrite (Ni0.72Fe0.20Co0.08Fe2O4),” Physical Review, vol. 107, no. 5, pp. 1246–1249, 1957.
[23]
V. A. Brabers, “Progress in spinel ferrite research,” in Handbook of Magnetic Materials, K. H. J. Buschow, Ed., vol. 8, North-Holland, Amsterdam, The Netherlands, 1995.
[24]
M. Grigorova, H. J. Blythe, V. Blaskov et al., “Magnetic properties and M？ssbauer spectra of nanosized CoFe2O4 powders,” Journal of Magnetism and Magnetic Materials, vol. 183, no. 1-2, pp. 163–172, 1998.
[25]
V. Blaskov, V. Petkov, V. Rusanov et al., “Magnetic properties of nanophase CoFe2O4 particles,” Journal of Magnetism and Magnetic Materials, vol. 162, no. 2-3, pp. 331–337, 1996.
[26]
N. Moumen, P. Veillet, and M. P. Pileni, “Controlled preparation of nanosize cobalt ferrite magnetic particles,” Journal of Magnetism and Magnetic Materials, vol. 149, no. 1-2, pp. 67–71, 1995.
[27]
E. Manova, B. Kunev, D. Paneva et al., “Mechano-synthesis, characterization, and magnetic properties of nanoparticles of cobalt ferrite, CoFe2O4,” Chemistry of Materials, vol. 16, no. 26, pp. 5689–5696, 2004.
[28]
L. Néel, “Thermoremanent magnetization of fine powders,” Review of Modern Physics, vol. 25, no. 1, pp. 293–295, 1953.
[29]
N. Menon and S. R. Nagel, “Evidence for a divergent susceptibility at the glass transition,” Physical Review Letters, vol. 74, no. 7, pp. 1230–1233, 1995.
[30]
G. A. Sawatzky, F. van der Woude, and A. H. Morrish, “M？ssbauer study of several ferrimagnetic spinels,” Physical Review, vol. 187, no. 2, pp. 747–757, 1969.
[31]
N. Moume, P. Bonville, and M. P. Pileni, “Control of the size of cobalt ferrite magnetic fluids: M？ssbauer spectroscopy,” Journal of Physical Chemistry, vol. 100, no. 34, pp. 14410–14416, 1996.
[32]
A. Hutlova, D. Niznansky, J.-L. Rehspringer, C. Estournès, and M. Kurmoo, “High coercive field for nanoparticles of CoFe2O4 in amorphous silica sol-gel,” Advanced Materials, vol. 15, no. 19, pp. 1622–1625, 2003.
[33]
S. R. Ahmed, S. B. Ogale, G. C. Papaefthymiou, R. Ramesh, and P. Kofinas, “Magnetic properties of CoFe2O4 nanoparticles synthesized through a block copolymer nanoreactor route,” Applied Physics Letters, vol. 80, no. 9, pp. 1616–1618, 2002.
