M R Anantharaman
Articles written in Bulletin of Materials Science
Volume 24 Issue 6 December 2001 pp 623-631 Magnetic Materials
Rubber ferrite composites containing various mixed ferrites were prepared for different compositions and various loadings. The magnetic and dielectric properties of the fillers as well as the ferrite filled matrixes were evaluated separately. The results are correlated. Simple equations are proposed to predetermine the magnetic and dielectric properties. The validity of these equations is verified and they are found to be in good agreement. These equations are useful in tailoring the magnetic and dielectric properties of these composites with predetermined properties.
Volume 25 Issue 7 December 2002 pp 599-607 Composites
The effect of frequency, composition and temperature on the a.c. electrical conductivity were studied for the ceramic, Ni1–𝑥Zn𝑥Fe2O4, as well as the filler (Ni1–𝑥Zn𝑥Fe2O4) incorporated rubber ferrite composites (RFCs). Ni1–𝑥Zn𝑥Fe2O4 (where 𝑥 varies from 0 to 1 in steps of 0.2) were prepared by usual ceramic techniques. They were then incorporated into a butyl rubber matrix according to a specific recipe. The a.c. electrical conductivity (𝜎a.c.) calculations were carried out by using the data available from dielectric measurements and by employing a simple relationship. The a.c. conductivity values were found to be of the order of 10–3 S/m. Analysis of the results shows that 𝜎a.c. increases with increase of frequency and the change is same for both ceramic Ni1–𝑥Zn𝑥Fe2O4 and RFCs. 𝜎a.c. increases initially with the increase of zinc content and then decreases with increase of zinc. Same behaviour is observed for RFCs too. The dependence of 𝜎a.c. on the volume fraction of the magnetic filler was also studied and it was found that the a.c. conductivity of RFCs increases with increase of volume fraction of the magnetic filler. Temperature dependence of conductivity was studied for both ceramic and rubber ferrite composites. Conductivity shows a linear dependence with temperature in the case of ceramic samples.
Volume 27 Issue 2 April 2004 pp 155-161 Magnetic Materials
Ultra fine precursors for ferrofluid synthesis, belonging to the series, Ni𝑥Fe1-𝑥Fe2O4 (where `𝑥’ varies from `0’ to `0.6’ in steps of 0.1), were synthesized. Ferrofluids based on these fine particles were prepared with oleic acid as surfactant and kerosene as carrier. Ferrofluidic thin films were made on glass substrates and magnetic field induced laser transmission was studied. The pattern exhibited by the films under the influence of a magnetic field was observed with the help of a CCD camera. The analysis of results confirms the chain formation of particles in the presence of an applied magnetic field and their saturation at higher applied fields.
Volume 27 Issue 4 August 2004 pp 361-366 Nanomaterials
Nanocomposites with magnetic components possessing nanometric dimensions, lying in the range 1–10 nm, are found to be exhibiting superior physical properties with respect to their coarser sized counterparts. Magnetic nanocomposites based on gamma iron oxide embedded in a polymer matrix have been prepared and characterized. The behaviour of these samples at low temperatures have been studied using Mössbauer spectroscopy. Mössbauer studies indicate that the composites consist of very fine particles of 𝛾-Fe2O3 of which some amount exists in the superparamagnetic phase. The cycling of the preparative conditions were found to increase the amount of 𝛾-Fe2O3 in the matrix.
Volume 29 Issue 2 April 2006 pp 159-163 Thin Films
Polyaniline is a widely studied conducting polymer and is a useful material in its bulk and thin film form for many applications, because of its excellent optical and electrical properties. Pristine and iodine doped polyaniline thin films were prepared by a.c. and rf plasma polymerization techniques separately for the comparison of their optical and electrical properties. Doping of iodine was effected
Volume 31 Issue 5 October 2008 pp 759-766 Magnetic Materials
Nano magnetic oxides are promising candidates for high density magnetic storage and other applications. Nonspherical mesoscopic iron oxide particles are also candidate materials for studying the shape, size and strain induced modifications of various physical properties viz. optical, magnetic and structural. Spherical and nonspherical iron oxides having an aspect ratio, ∼2, are synthesized by employing starch and ethylene glycol and starch and water, respectively by a novel technique. Their optical, structural, thermal and magnetic properties are evaluated. A red shift of 0.24 eV is observed in the case of nonspherical particles when compared to spherical ones. The red shift is attributed to strain induced changes in internal pressure inside the elongated iron oxide particles. Pressure induced effects are due to the increased overlap of wave functions. Magnetic measurements reveal that particles are superparamagnetic. The marked increase in coercivity in the case of elongated particles is a clear evidence for shape induced anisotropy. The decreased specific saturation magnetization of the samples is explained on the basis of weight percentage of starch, a nonmagnetic component and is verified by TGA and FTIR studies. This technique can be modified for tailoring the aspect ratio and these particles are promising candidates for drug delivery and contrast enhancement agents in magnetic resonance imaging.
Volume 34 Issue 2 April 2011 pp 245-249
Ferrofluids belonging to the series, Ni𝑥Fe1−𝑥Fe2O4 and Zn𝑥Fe1−𝑥Fe2O4, were synthesized using cold co-precipitation. Liquid films of these ferrofluids were prepared by encapsulating the ferrofluids in between two optically smooth and ultrasonically cleaned glass plates. Magnetic field induced laser transmission through these ferrofluid films has been investigated. Magnetic field values can be calibrated in terms of output laser power in the low field region in which the variation is linear. This set up can be used as a cheap optical gaussmeter in the low field regime. Using the same set-up, the saturation magnetization of the sample used can also be calculated with a sample that is pre-characterized. Hence both magnetization of the sample, as well as applied magnetic field can be sensed and calculated with a precalibrated sample.
Volume 34 Issue 2 April 2011 pp 251-259
Zinc aluminate nanoparticles with average particle size of 40 nm were synthesized using a sol–gel combustion method. X-ray diffractometry result was analysed by Rietveld refinement method to establish the phase purity of the material. Different stages of phase formation of the material during the synthesis were investigated using differential scanning calorimetry and differential thermogravimetric analysis. Particle size was determined with transmission electron microscopy and the optical bandgap of the nanoparticles was determined by absorption spectroscopy in the ultraviolet-visible range. Dielectric permittivity and a.c. conductivity of the material were measured for frequencies from 100 kHz to 8 MHz in the temperature range of 30–120°C. The presence of Maxwell–Wagner type interfacial polarization was found to exist in the material and hopping of electron by means of quantum mechanical tunneling is attributed as the reason for the observed a.c. conductivity.
Volume 35 Issue 1 February 2012 pp 41-45
Materials belonging to the family of manganites are technologically important since they exhibit colossal magneto resistance. A proper understanding of the transport properties is very vital in tailoring the properties. A heavy rare earth doped manganite like Gd0.7Sr0.3MnO3 is purported to be exhibiting unusual properties because of smaller ionic radius of Gd. Gd0.7Sr0.3MnO3 is prepared by a wet solid state reaction method. The conduction mechanism in such a compound has been elucidated by subjecting the material to low temperature d.c. conductivity measurement. It has been found that the low band width material follows a variable range hopping (VRH) model followed by a small polaron hopping (SPH) model. The results are presented here.
Volume 38 Issue 3 June 2015 pp 689-694
The incorporation of nanoparticles of iron in a natural rubber matrix leads to flexible magnetorheological (MR) materials. Rod-shaped MR elastomers based on natural rubber and nanosized iron have been moulded both with and without the application of an external magnetic field during curing. These MR elastomer rods and filler material were characterized by X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. Magnetic properties were investigated by using vibrating sample magnetometry. Microactuation studies were carried out by employing a laser Doppler vibrometer. It is seen that microactuation of field cured samples have been enhanced by two times when compared with that of zero field cured samples. The effect of alignment of magnetic particles during field-assisted curing was also studied by using a dynamic mechanical analyzer. A plausible model is put forwarded to explain the observed enhancement of actuation for field cured samples.
Volume 38 Issue 6 October 2015 pp 1545-1552
Present investigation focuses on the variation of magnetic entropy change for higher sodium substitution above 50% in lanthanum manganites. Magnetic measurements indicated that all samples exhibit a ferromagnetic ordering near room temperature. Magnetic isotherms for different temperatures above and below 300 K were recorded and the magnetic entropy change for compositions belonging to La1−𝑥Na𝑥 MnO3 for 𝑥 = 0.6 to 0.9 in steps of 0.1 was estimated for different applied magnetic fields. It has been found that the compositions having a Na substitution of 0.6 are having the largest entropy change, and the entropy change increases with applied magnetic field for all compositions. The change in entropy also decreases with increase in substitution of sodium. A notable change in transition temperature with Na concentration is also found in this sample series.
Volume 42 | Issue 5