Publications

In the reported research work, we investigated the structural, thermal, magnetic, surface morphology, Raman spectroscopic and dielectric properties of Cu-Cr co-substituted M-type barium hexaferrites for lossless low-frequency applications. By using the green synthesis approach with mentha leaves extract, we synthesized a series of M-type BaCuxCrxFe12‐2xO19 (0.0 ≤x≤0.5) hexaferrite with varying Cu-Cr content. A simple heat treatment method was used to prepare hexaferrite samples. The samples were heated to 1100 °C and thoroughly characterized for their structural, thermal, magnetic, Raman spectroscopic and low frequency dielectric study. The results of XRD finding revealed the formation of M-phase along with secondary phase of BaFe2O4. The Raman spectroscopic analysis shows the successful replacement of Cu and Cr ions in place of Fe ions, and the substituted samples hold the hexagonal shape as visible from FESEM images. All samples show a hard magnetic nature with multi-domain structures, and x = 0.2 composition has a maximum Ms of 68.99 Am²/kg and lowest Hc of 0.1 T. Cole-Cole graphs show shifting of peaks position with Cu-Cr substitutions and increasing frequency, which gives the insight of the role of grain and grain boundaries. These findings open up exciting possibilities for using these hexaferrites in loss-less, and low-frequency applications.

A series of M-type lanthanum substituted strontium cobalt hexaferrites, Sr0.5Co0.5LaxFe12-xO19(x=0.0, 0.05, 0.15 and 0.2) was synthesized using the simple heat treatment method. The synthesized hexagonal ferrites were calcinated at 950°C and 1050°C for 3 hrs in a muffle furnace and then slowly cooled to room temperature. X-ray diffraction (XRD) technique and magnetic hysteresis loops were used to investigate the structural and magnetic properties of prepared samples respectively. The X-ray diffraction analysis of all the samples shows the presence of M- type hexagonal ferrite and hematite phases. Room temperature magnetic hysteresis loops analysis shows the increase in saturation magnetization with the increase in lanthanum substitution.

X-type samarium-cadmium co-substituted hexaferrite with compositions Ba2-xSmxCo2CdyFe28-yO46 (0.00 ≤ x ≤ 0.08, and 0 ≤ y ≤ 0.4) were prepared at 1340 °C using a simple heat treatment technique. All heated samples were characterized using FTIR, XRD, SEM, VSM, Mӧssbauer, and low-frequency dielectric measurements. XRD analysis of prepared samples shows the formation of X as a major phase along with hematite. The MS value varied from 67.01 Am²/kg to 50.43 Am²/kg; whereas the Hc value changed from 2.95 kA/m to 6.17 kA/m, A high value of MS (67.01 Am²/kg) is observed in the pure sample, and a very low value of Hc (2.95 kA/m) is observed for x = 0.06, y = 0.3 compositions, but Mr/Ms < 0.5 confirm the multi-domain nature of prepared hexaferrites. Hysteresis loops of all samples are narrow, and confirmed that formed samples belong to magnetically soft. Mössbauer spectra of the three samples (S1, S3, and S5) show the existence of doublets. Significantly low values of coercivity, retentivity, and loss tangent in Sm–Cd substituted samples signified those prepared materials can be used to design electromagnets, transformer cores, electric motors, and maybe a potential candidate for lossless low-frequency applications.

In the present work, we report the structural and microstructural properties of hematite (α-Fe2O3) synthesized using the co-precipitation method. Oleic acid was used as a surfactant in the synthesis process to reduce the agglomeration. Prepared hematite samples were characterized using FTIR, XRD, SEM, DLS and UV-VIS spectroscopic measurements. FTIR analysis of α-Fe2O3 shows the presence of Fe-O bands in the wavenumber range of 400 to 750cm-1. X-ray diffraction analysis of hematite powder prepared without oleic acid confirms the formation of the pure phase of α-Fe2O3. SEM image reveals that the formation of spherical particles with an average size < 200nm and it is in a good agreement with particle size distribution observed from Dynamic Light Scattering. A UV-Vis spectroscopic result shows strong absorption in the UV region and weak absorption in the visible region.

M-type calcium hexaferrite- CaFe12O19 (CaM) has been prepared in presence of Azadirachta indica, and Murraya koenigii leaves extracts, followed by calcination at 650 °C for 3h. It was observed that the presence of phytochemicals in both leaves extract plays a vital role in deciding the structural, optical, microstructural, magnetic, and dielectric properties of prepared CaM hexaferrites. Prepared samples were characterized using FT-IR, XRD, UV–Vis, SEM, VSM, and dielectric measurements. FTIR, UV– Vis, and antioxidant assay confirmed the presence of phenolic content and antioxidant property of plant extract. This further resulted in the formation of a pure hexagonal phase as revealed by the XRD analysis. The surface morphology of prepared ferrites modified through this greener route was illustrated by the spongy appearance of ferrites in SEM micrographs.The saturation magnetization for the CaM powder prepared using Murraya koenigii leaves extract is 11.78 Am²/kg, while that prepared from Azadirachta indica leaves extract is 3.56 Am²/kg. Both samples show a magnetically soft nature, with a multidomain structure. The energy bandgap was also observed to be 2.01 eV. Moreover, the calcium ferrite synthesized by Murraya koenigii leaves had ε’max ∼ 25 and that synthesized in presence of Azadirachta indica leaves had ε’max ∼ 200 at ∼20 Hz.

M-type, Ba0.4Pb0.6Fe12-xCoxO19 (x = 0.00, 0.10, 0.20, 0.30, 0.40) hexaferrites, synthesized using citrate gel auto combustion method, and heated at 950 °C, 4 h for lossless applications. XRD analysis shows the development of the M-phase, along with PbM and hematite. The microstructural analysis reveals the stacking clusters of hexagonally shaped platelets. TEM image and SAED pattern of x = 0.3 composition shows polycrystalline nature and formed particles observed to fused with neighbouring particles. M − H loops of all samples reveal hard magnetic behaviour and possess multi-domain structure. The maximum saturation magnetization of 55.427 A m²/kg is observed in x = 0.10 composition and coercivity of prepared hexaferrites was found to vary from 0.058 T to 0.390 T. The cobalt substitution has a strong influence on the dielectric properties of prepared hexaferrites. The value of ac conductivity increases with cobalt substitution from x = 0.00 to x = 0.10, and followed by a reduction from x = 0.10 to x = 0.40. The same trend is observed for the dielectric constant. The low value of loss tangent for all compositions shows apt scope for lossless application.