• K A Malini

      Articles written in Bulletin of Materials Science

    • Tailoring magnetic and dielectric properties of rubber ferrite composites containing mixed ferrites

      M R Anantharaman K A Malini S Sindhu E M Mohammed S K Date S D Kulkarni P A Joy Philip Kurian

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      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.

    • Evaluation of a.c. conductivity of rubber ferrite composites from dielectric measurements

      S Sindhu M R Anantharaman Bindu P Thampi K A Malini Philip Kurian

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      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.

    • Low temperature Mössbauer studies on magnetic nanocomposites

      K A Malini M R Anantharaman Ajay Gupta

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      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.

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