Ferrites
Ferrites are mixed metal oxides with iron in oxidation state of +3 as the main component. Electrically, they are bad conductors and display magnetic properties. The most common ferrites have the general formulae MFe2O4 and MFe12O19, where M stands for a divalent metal such as Nickel(Ni), Cobalt(Co) etc. Ferrites have been receiving growing attention because of their various commercial and technological applications(1,2). Spinel and magnetoplumbite ferrites are very important and exhibit ferrimagnetism. Their hysteresis loop is almost rectangular(3). For this reason, they are used in high frequency circuits as a magnetic cores and in switching devices.
Nanoparticles
Nanoparticles are particles in the range of size 1nm to 100 nm. The understand the properties, behavior and structure of particles in this scale is Nanoscience. Nanotechnology is application of nanoscience in development of newer tools. There are two facets, one is the development of devices of very small sizes and the other is the improvement of existing materials by reduction of sizes. The size reduction increases the surface to volume ratio, free energy content, band-gap, as well as defect concentration(4). This way, nanomaterials acquire some exotic properties which are not available in Bulk materials. Quantum confinement and surface effect plays an important role in modifying the properties of nanomaterials. Because of the extremely small particle size, the continuum energy bands become quantized into discrete energy levels. Due to these reasons, the structural, electronic, magnetic and optical properties that we observe in bulk size get modified in nano size(5), which depend on size, shape, composition and method of preparation. As for examples Chalk and seashell are made of same materials, calcium carbonate. Chalk is shoft while seashell is hard. This is because the shells made of nanostructured materials.
In the Nanocrystalline phase ferrites exhibited properties that are notably different from their bulk phase properties and strongly dependent on the conditions and preparation techniques (6,7). In this Characterization:
The ferrite nanoparticles are characterized after their preparation using various characterizing tools, such as X-ray diffraction(XRD), Vibrating sample magnetometer(VSM), Transmission electron microscopy(TEM), Mossbaur spectroscopy, Scanning electron microscopy(SEM), Positron annihilation spectroscopy, Superconducting quantum interface devices(SQUID), and UV-VIS spectroscopy etc. The mean particle size,shape and phases are determined using X-ray diffraction method. Magnetic properties were measured usind SQUID and VSM. TEM gives information about particle size distribution while SEM gives particle morphology. Mossbaur spectroscopy gives information about percentage of iron content and superparamagnetic behavior. Positron annihilation spectroscopy is a powerful experimental tool for probing the electronic and defect structure of solids(9).
Figure no. 3: Hysteresis curve for Zn Ferrite nanoparticles (9)
Ferrites and ferrites based composite materials have wide applicability in the fields of integrated electronics, microwave devices, sensors and transducers, magnetic cores, electromagnets, magnetic storage devices. We have not come to the stage where we can suggest new technological applications. But possibility of such leads in future cannot be ignored. We will have to continue with this exploratory work.
Acknowledgements: Thankful to Prof. H.C.Verma, Dr.M.K.Roy, Dr.B.Paday, Deptt of Physics, I.I.T Kanpur, Dr. Amarendra Narayan, Deptt of Physics, Patna University, Prof. A.Yadav, Former V.C and presently chief co-ordinator, School of Pure Science(PG), NOU, Patna, Dr. Sister doris D.Souza A.C.,Principle Patna women’s College, Prof. Girija Gupta, head, Deptt of Physics, Patna Womens College, Prof. A.C.Pandey, University of Allahabad, Dr. Santosh kumar, B.S.College Danapur for useful discussion and academic support.
References:-
1. Mitsuo Sugimoto, The past, Present and Future of Ferrites, J.Am.Ceram Soc. 82(2),269-280 (1999)
2. F. Mazaleyrat et al., Ferromagnetic nanocomposites, J.magn.magn. mater. 215-216, 253-259 (2000).
3. J. Smit and H.P.J. Wijn, Ferrites,p44 ( Philips technical Library, U.K.Edition, London, 1959)
4. R.P.Singh, Invited talk, National workshop on nanomaterials and Nanotechnology, Lucknow Univ. Abstr. (2007),p4.
5. M. Ratner, D Ratner, Nanotechnology, A gentle Introduction to the next Big Idea (Prentice Hall, 2003) P.13.
6. S. Hilpert and R. Schweinhagen, Ferrites, III(In German) Z.Phys.Chem. B31, 1-11(1935)
7. Yshizawa, S. Oguma, K.Yamaauchi, J.Appl.Phys.64, Bioengineering, Vol. 4, p 606-613(2002). 6044 (1988). 21. Ivo Safarik and Mirka Safarik, magnetic nano particles in biological sciences, Nano ’02 pp 73-78 (2002)
8. M. Pal and D. Chakravorty, Nanocrystalline Magnetic Alloys and Ceramics, 28, p283-287(2003).
9. A.narayan, Rakesh Kumar Singh, Binay Kumar, H.C.Verma, M.K.Roy and Brajesh Pandey,p11- 13,Patna University Journal, Vol.31, no.1, (March 2007).
22. N. Ponpandian and A. Narayanasamy, Influence of grain size and structural changes on the electrical properties of nanocrystalline zinc ferrite, journal of applied Physics, volume 92, number 5, 1 September
10. Rakesh kumar Singh, Amarendra Narayan, X-ray 2002. diffraction, An investigation tool for nanomaterials, proceeding of national conference on convergence with physics, Jamshedpur (2007) p. 118-121.
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phase the special emergence properties such as superparamagnetism, collective magnetic excitations, spin canting is to be found. Growth of ferrite nanoparticles
There are several routes for preparation of nanocrystalline ferrite samples. One method that has been used widely is by powdering. Ball milling are normally employed for this. Fine powders have also been obtained using chemical precipitation and annealing. Electrolytic techniques have also been used. Several other methods exists besides these. A review of the different preparation techniques has been given by M.Pal and D.Chakravorty(8). Each of these techniques has its own advantage and disadvantage. The chemical route has a number of attractive features like simplicity and low cost of preparation so that it become an attractive for preparation of nanocrystalline phase ferrite. In chemical based citrate precursor method, generally nitrates of divalent metal, Iron and citric acid are taken in stoichiometric proportions and dissolve in minimal amount of disstiled water. The aqous solutions are mixed together and stirred at 600c to 80oC temperature for two hours. A Brown slurry is formed, which is then dried in an oven at a temperature of 90 oC. This dried materials is the citrate precursor(Figure 01). Ferrite nanomaterials are produced by annealing of the dehydrated precursor at predetermined temperatures in a temperature controlled muffle furnace.
For example we take zinc ferrite (10). The average particle size of Zinc ferrite sample was determined as 11.37nm using Scherrer equation ( d= k?/ßcos?)at 450oC and 33 nm at 650oC. Where k is constant that has value 0.9 and B is full width at half maximum. For this analysis, we used the most prominent peak( Figure 02).. The average coercive field and saturation magnetization of the this nanoparticle are 2.87Oe and 3.99 emu/g. The retentivity is 1.152 x 10-3 emu/g. We find average particle size increases as annealing temperature increased. Also the magnetic parameters value changes with particle size.
Technological applications for ferrite nanoparticles.
Ferrites have a broad range of applications in many disciplines. These include products and applications such as transformer cores for power applications.11,12,13 Multilayer ferrite chip inductors14, Microwave ferrite devices15,16, ferrite wave absorbers17, Magnetic recording media18, ferrite magnets19, etc. In the field of medical sciences also, ferrites are finding numerous applications. Magnetic nanoparticles have unique magnetic features that can be applied to specific medical techniques20. These include separation, immunoassy, magnetic resonance imaging, and many others.
Drug delivery and hyperthermia are enhanced by use of appropriate magnetic particles. Magnetic cationic lipsomes (MLCs) can be used as carriers for introducing DNA into cells and heat mediators for cancer therapy.
There are other applications related to biological sciences. Applications include immobilization and modification of biologically active compounds by magnetic carriers, isolation of biologically active compounds, detection of biologically active compounds and xenobiotics, modification, detection, isolation and study of cells and cells organelles can all be effectively carried out with the help of magnetic nanoparticles.21,22
11. S. Murayama et al., High strength Ni-Cu-Zn Ferrite for surface mounted devices, Proc. 6th International Conf. on Ferrites (Tokyo and Kyoto, Japan, Sept. & Oct.1992) p 366-369. 12. T. Ochiai and K. Okutani, Ferrites for High Frequency Power Supplies, Advances in Ceramics Vol. 16, p447-456 (Ed. F.F.Wang, Am. Ceram. Soc. Columbus, O. 1986) 13. Anjali Verma et al.,Development of a new soft ferrite core for power applications, Communicated to Jour. Magnetism and Magnetic Materials (2005) 14. M. Takaya, Multilayer integrated surface mount device, Proceedings of international symposium on micro electronics (Tokyo, Japan 1988) p25-32. 15. C. Dattatreyan, Theory and design of non reciprocal microwave Ferrite devices: Isolators and circulators. Ferrite materials (Edited by B. Viswanathan and B. R. K. Murthy, Narosa Pub. House New Delhi(1990) 16. S. Capararo et al., Barium Ferrite thick films for Microwave Applications, Jour. Mgnetism and Magnetic Materials, 272-276, e1805-e1806 (2004) 17. H. Ueno, T. Yasuyoshi and S. Yoshikado, Fabrication of the composite Ferrite Electromagnetic wave absorber. J Magn. Soc. Japan,22, 369-371 (1998) 18. G. Bate, the present and future of magnetic recording media. Proceedings of third international conference on Ferrites (Kyoto Japan, 1980) ed. H.Watanabe, S. Iida, and M Sugimoto, Centre for academic publications, Tokyo Japan 1981, pp509-515. 19. W In .G. Hart, The global magnetic material market – past, present and future, in abstract of the 15th anniversary symposium of the Japan association of bonded magnet industries (Tokyo, Japan, 1996), pp 1- 15 20. Masashige Shinkai, Functional magnetic particles for Medical applications, Journal for Biosciences and Bioengineering, Vol. 4, p 606-613(2002 21. Ivo Safarik and Mirka Safarik, magnetic nano particles in biological sciences, Nano ’02 pp 73-78 (2002) 22. N. Ponpandian and A. Narayanasamy, Influence of grain size and structural changes on the electrical properties of nanocrystalline zinc ferrite, journal of applied Physics, volume 92, number 5, 1 September2002. |