Papers by Author: Rajshree B. Jotania

Abstract: The W type barium magnesium hexaferrite powder with chemical composition BaMg₂Fe₁₆O₂₇with CTAB surfactant was synthesized using solvent free synthesis method. The precursor was calcinated at 950 °C for 6 h in a muffle furnace and then slowly cooled to room temperature in order to obtain barium magnesium hexaferrite powder. The flexible epoxy thick film of Ba-Mg hexaferrite/epoxy composite was fabricated using suitable amount of hardener and curing agent. The field-dependent magnetic properties of the hexaferrite sample were investigated at room temperature using a vibrating sample magnetometer (VSM) with a maximum applied field of 15 kOe. The dielectric measurements were taken at room temperature within the frequency range to 100 Hz to 2 MHz.

Abstract: Influence of Ca substitution on structural, magnetic and dielectric properties of Ba₃Co_2-xCa_xFe₂₄O₄₁ (where x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), prepared by Sol-Gel auto-combustion method, has been investigated in present studies. The obtained powder was sintered at 950 oC for 4 hrs. in the static air atmosphere. Structural analysis of Ca-doped Ba₃Co_2-xCa_xFe₂₄O₄₁ powders revealed pure Z-type hexaferrite phase at low temperature. The frequency dependent dielectric constant (Єʹ) and magnetic properties such as remanent magnetization (Mr), saturation magnetization (Ms) and coercivity (Hc) were studied. It is observed that coercivity increased gradually with increase in calcium content. The real dielectric constant (Єʹ) and dielectric loss tangent (tan δ) were studied in the frequency range of 20Hz to 2MHz. The dielectric parameters for all samples show normal dielectric behavior as observed in hexaferrites. Contents of Paper

Abstract: Z-type hexaferrite with composition Ba₃Co₂Fe₂₄O₄₁ has been synthesized using a sol-gel auto combustion technique. The obtain combusted powder was sintered at 500 OC and followed by 950 OC for 4 hrs in a muffle furnace. The effect of different sintering temperature on crystal structure, crystallite size, microstructure and dielectric properties were systematically investigated. The prepared barium cobalt hexaferrite powder samples were characterized using different experimental techniques like FTIR, XRD, AC conductivity and specific magnetization measurements. It was observed from XRD results that heat treatment conditions play significant role in the formation of hexaferrite phase. AC conductivity measurements were carried out at room temperature in frequency range of 20Hz to 2MHz. All the samples show the frequency dependent phenomena, i.e. the AC conductivity increases with increasing frequency.

Abstract: Cobalt ferrite (Cofe₂o₄) particles were synthesized with and without presence of surfactants using a co-precipitation method. Three surfactants Cetyl Tri methyl Ammonium Bromide (CTAB-cationic), Sodium dodecylbenzenesulphonate (anionic), Triton X-100 (nonionic), were used and investigate their effects on the structural and dielectric properties of CoFe₂O₄ particles. The ferrite precursors were first pre calcined in a muffle furnace at 500°C and then calcined at 950^°C. Structural, dielectric and magnetic properties of prepared particles were investigated using X-ray powder diffraction, Dielectric and Low field ac magnetic susceptibility measurement. Phase purity of prepared samples was confirmed by X-ray diffraction. The sample with surfactant Triton X-100 shows the highest values of dielectric constant at low frequency.

Abstract: The preparation and characterization of composite materials containing nanometer-sized constituents is currently a very active and exciting area of research at laboratories around the world. In order to improve the magnetic and electromagnetic absorption properties of magnetic materials, composite of soft/hard ferrite is required in proper composition. For high-density magnetic recording, decrease in the coercive field and simultaneously increase in saturation magnetization has attracted much attention. To achieve these properties, new modified CoFe₂O₄-SrFe₁₂O₁₉ composite ferrite nanoparticles were prepared by using an SHS route. Composites of spinel: hexaferrite were prepared in the ratio 1:0, 1:2 and 0:1. The enhancement of maximum energy product BH_max is achieved by the addition of Spinel ferrite into M-type hexaferrite particles. The exchange interactions between hard and soft magnetic phases improve the microwave absorption properties. The parameters, H_c, σ_s, and particle size d, can easily be controlled by changing the content of spinel ferrite in the composite with Sr-M hexaferrite.

Abstract: In the present study, a series of Cu substituted M type Barium hexagonal ferrite BaCuxFe12-xO19 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) has been synthesized using a Sol- gel auto combustion method. The aim of the present work was to investigate the effects of Cu/Fe ratio on the crystallography and dielectric properties. The XRD studies reveal a formation of the single phase BaFe12O19 at the initial level and mixed phase of S, M and Y hexaferrite at the higher level of copper substitution. The dielectric measurements were carried out at room temperature in a frequency range of 20 Hz to 2MHz. the dielectric constant is found to decrease with the increase of frequency for all the compositions.

Abstract: The W type barium zinc hexaferrite sample was prepared by a solvent free method with and without presence of cationic surfactant CTAB. The precursors were calcinated at 950°C for 4 hrs in a furnace to obtained BaZn2Fe16O27 crystalline ferrite powder. The effect of proportion of surfactant on structural properties of hexaferrite was studied. The hexaferrite powder was characterized by using various instrumental techniques like XRD and SEM. The structural properties of the samples were investigated by using XRD and SEM. The SEM images of the sample in presence of surfactant shows that surfactant controls the morphology of the particles.

Abstract: Swift heavy ion irradiation of material is a unique tool to modify the properties of the material and it provides an alternative to photons for introducing electronic excitations into the material. In the present investigation, the changes in structural, morphological and magnetic properties of SrFe₁₂O₁₉ ferrite (prepared using co-precipitation and SHS routes), induced by 200 MeV Ag⁺¹⁶ ion irradiation have been studied. In order to study the effect of the electronic stopping power (dE/dX) e on these properties the energy of the projectile was so chosen that it could easily pass through the samples. Structural properties of these ferrites have been studied and compared with the properties after Swift Heavy Ion (SHI) irradiation of 200 MeV Ag¹⁶⁺ at different fluences. Samples were characterized using different experimental techniques, like Fourier Transform Infra-red (FT-IR), X-ray Diffraction (XRD), Scanning Electrom Microscope (SEM), Vibrating Sample Magnetometer (VSM) and LCR meter. FTIR spectra for pristine as well as the irradiated samples were recorded for wave number ranges from 4000-400 cm^-1 using the KBr pellet method. FTIR measurement of the bonds' vibration modes in all samples were carried out to determine the change in MO bonding due to irradiation. The MO absorption band is observed in all samples. The intensity of absorption bands increased in irradiated samples, which confirms the formation of strong ferric oxide band. Crystallinity of pristine and irradiated samples was investigated by XRD technique. All XRD peaks were indexed using POWDER X software. XRD result confirms the formation of mono phase. It is observed from XRD analysis that after the irradiation, the intensity of all the peaks and FWHM were increased. There is no significant change in peak position but the intensity is decreased and FWHM is increased continuously with ion fluence. XRD patterns confirm that the ferrite structure is retained even after irradiation. Surface morphology of pristine and irradiated samples was studied using a scanning electron microscopy. It is observed from SEM images that the particle size decreases after irradiation and particles become more homogeneous. Dielectric and magnetic measurements were also carried out.

Abstract: SrFe₁₂O₁₉ hexaferrite particles containing polyoxyethelene (20) sorbitan monolate (Tween-80) were synthesized by a chemical co-precipitation technique with a precipitator NH₃.H₂O. The prepared Sr-M hexaferrite precipitates were heat treated at various temperatures 650 oC, 750 oC, 850 oC, 950oC and 1100oC for 4 hrs in a muffle furnace. The obtained Sr-M powders were characterized by using various instrumental techniques, like FTIR, TGA, XRD, SEM, VSM and Mössbauer spectroscopy. Their physical as well as Magnetic properties were compared. It was observed from XRD results that heat treatment conditions play significant role in the formation of pure SrFe₁₂O₁₉ hexaferrite phase and also in the grain size. The estimated particle size is of the order of nanometer when suitable calcination temperature is applied. SEM micrographs show an increase in crystallite size of the resultant SrFe₁₂O₁₉ hexaferrite particles sintered at higher temperature (1100 oC). Mössbauer spectroscopic measurements were carried out at room temperature. Mössbauer analysis indicates the presence Fe³⁺ ions in the prepared strontium hexaferrite particles.

Abstract: W-type hexagonal ferrite with composition BaCa₂Fe₁₆O₂₇ was prepared using a stearic acid gel method. The precipitate of barium calcium hexaferrite was calcinated at 650°C, 750°C, 850°C and 950°C in a furnace for 4 hours and then slowly cooled to room temperature. The dielectric constants (real Є and imaginary Є), conductivity (σ) and dielectric loss (tan δ) have been measured at room temperature as a function of frequency (10²-10⁶ Hz). The dielectric behavior of prepared hexaferrite samples can be explained by the mechanism of polarization and the electrical conduction mechanism is explained by using the electronic hopping model of Heike Johnson.