IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

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Chapter -6 BASIC RESEARCH VI.1. Field-Induced Extinction of Light in a Magnetic Nanofluid A magnetically triggered extinction of light in a disordered magnetic medium, i.e., a colloidal suspension of Fe 3 O 4 nanoparticles, has been observed. In this system, the size parameter and the magnetic permeability of the scatterer is tuned by changing the applied magnetic field. Both the forward and backward scattered light intensity as a function of applied magnetic field and the critical magnetic fields where both the forward and backward scattered light intensities drop to zero are measured. A stable colloidal suspension of magnetite (Fe 3 O 4 ) nanoparticles of average diameter 6.7nm, coated with oleic acid and dispersed in kerosene is used. The organic layer thickness around the particles is about 1.5nm. The experimental setup is shown in Fig.1. The ferrofluid
IGC Annual Report 2007 sample is taken in a quartz cuvette and kept inside a solenoid, where magnetic field is varied by changing the current passing through its coil using a DC power supply. The direction of magnetic field is parallel to the wave propagation. An amplitude and frequency stabilized polarized He-Ne laser (Spectra-physics) of wavelength 632.8 nm with an output power of 1 mW is used as the light source. The light intensity is measured by using a photomultiplier tube (Oriel). The output of the PMT is fed to readout through a current amplifier with variable gain. The analog output from the readout is connected to a 12 bit analog to digital converter (ADC) that is interfaced with a computer. For observation, the light scattered from the sample is projected on a screen and recorded using a CCD camera. The transmitted light intensity through the samples has been acquired as a function of external magnetic field. Fig.2 shows the transmitted intensity as a function of external field for different magnetite volume fractions. The intensity plotted was the ratio of the intensity transmitted through the sample with and without magnetic field. Here, at lower concentrations, the transmitted light intensity remains constant upto a critical magnetic field (H C1 , shown by the dotted arrow) and above which the intensity starts to decrease drastically. At another critical magnetic field H C2 , shown by the solid arrow in Fig. 2, the transmitted light intensity becomes a minimum. Above H C2 , the transmitted light intensity increases slowly. The forward scattering patterns from a magnetite suspension of 0.0067 volume fraction of Fe 3 O 4 at various magnetic fields are shown in Figure 3. Here, the transmitted light intensity drops to zero at a magnetic field strength of 115Gauss, above which the forward scattered light shows a diffused ring like structure i.e. when the applied magnetic field is above H C2 . The ring becomes sharper as the magnetic field strength increases further. It has been found that both H C1 and H C2 follow a power law decay with volume fraction (H C ∞φ -x ) where the exponents are 0.423 and 0.283 respectively. Also, with increasing concentration, the slope of the transmitted intensity curve (between H C1 and H C2 ) increases. Without any external magnetic field, the magnetic moments of the scatterers are oriented in random direction. With the increase in magnetic field, the moments of the magnetic particles start to align along the direction of the magnetic field. The lengths of the chains Fig.1 A schematic of the experimental set up. The direction of the applied magnetic field is along the direction of propagation of the beam. P-polarizer, SC-sample cuvette, S-solenoid, M-mirror, PMT-photomultiplier tube and IF-interference filter. BASIC RESEARCH 145
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“Actions today mould our tomorrow
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Editorial Committee Chairman Dr. P.
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widely acclaimed nationally and int
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Chapter -1 FAST BREEDER TEST REACTO
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IGC Annual Report 2007 Active fuel
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IGC Annual Report 2007 I.3. Seismic
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IGC Annual Report 2007 I.4. Validat
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Chapter -2 PROTOTYPE FAST BREEDER R
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IGC Annual Report 2007 Fig.1 Therma
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IGC Annual Report 2007 Fig.1 Schema
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IGC Annual Report 2007 Fig.2 Finite
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IGC Annual Report 2007 Fig.1 PFBR p
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IGC Annual Report 2007 III.A.3. Inv
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IGC Annual Report 2007 T* 1,00 0,80
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IGC Annual Report 2007 intermediate
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IGC Annual Report 2007 III.C.3. Imp
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IGC Annual Report 2007 8mm diameter
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IGC Annual Report 2007 (~15 s -1 )
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IGC Annual Report 2007 III.C.9. Eff
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IGC Annual Report 2007 the nitrided
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IGC Annual Report 2007 III.D. Contr
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IGC Annual Report 2007 that the eff
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IGC Annual Report 2007 III.E.5. Sim
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Chapter -4 FUEL CYCLE IV.A. Fuel Pr
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IGC Annual Report 2007 IV.A.7. Deve
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Page 193 and 194: PUBLICATIONS - 2007 Journal Publica
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Chairman IGC COUNCIL MEMBERS Dr. Ba
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anomalous transport, MARFES, solito
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sioning activities of the Captive P
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Indira Gandhi Centre Scientific Com
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Fast Reactor Technology Group Shri
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The Reprocessing Group (Rp G)of IGC
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Electronics and Instrumentation Gro
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Smt. Uma Seshadri Head, PD Planning
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