Rajshree B. Jotania

Effect of sintering temperature and vinca petals extract on structural and magnetic properties of delafossite CuFeO2

Delafossite CuFeO2 multiferroic powder was synthesized using Sol-Gel auto combustion method. Influence of vinca flower petals extract on structural and magnetic property of CuFeO2 were investigated. X-ray analysis of normal samples (synthesized without presence of vinca petals extract) shows formation of hematite and ferrite phases while the sample synthesized in presence of vinca petals extract show only mono phase. The absorption bands in FTIR spectra present between 510-460 cm−1 in both the samples are due to stretching of Fe-O vibrations. VSM analysis shows that the squareness ratio (Mr/Ms) of the sample prepared using vinca petals extract obtains value of squareness ratio < 0.5, which attributes multi domain formation of samples.

Y-Type Hexaferrites: Structural, Dielectric and Magnetic Properties

This paper attempts to provide a historical survey of structure of various types of hexaferrites. It provides information about synthesis, characterization, structural, magnetic and dielectric properties of Y-type hexagonal ferrites using various chemical routes. We have prepared a series of cobalt doped Sr2Cu2-xCoxFe12O22 (x = 0.0 to 1.0) hexaferrites using a wet chemical co-precipitation technique. The prepared hexaferrite precursors were calcined at 950 °C for 4 hours in a furnace and slowly cooled to room temperature. The crystal structure of Y-type hexaferrites is rather complicated. The chemical and structural changes were examined in detail by X-ray diffraction (XRD), Differential scanning calorimetry (DSC), Scanning electron microscopy (SEM), and Fourier transform infra-red (FTIR) spectroscopy. X-ray diffraction studies showed that sintering temperature as low as 950°C was sufficient to produce a single-phase Y-type hexaferrite material. The dielectric measurements were carried out over the frequency range of 100 Hz to 2 MHz at room temperature using an LCR meter to study the variation of dielectric constant and loss tangent with frequency. The magnetic properties of hexaferrite samples were investigated using a vibration sample magnetometer (VSM), and a superconducting quantum interference device (SQUID) magnetometer in the temperature range 30K to 200K. A change from ferromagnetic state to super paramagnetic state has been observed in Co doped Sr2Cu2-xCoxFe12O22 (x= 0.6 to 1.0) hexaferrite. The novel applications of all types of hexaferrite materials have been described.

Effect of Surfactants on Structural and Dielectric Properties of Cobalt Ferrite

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.

Enhancement of Magnetic Properties in Co-Sr Ferrite Nano Composites Prepared by an SHS Route

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 BHmax 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, Hc, σs, and particle size d, can easily be controlled by changing the content of spinel ferrite in the composite with Sr-M hexaferrite.

Structural and Dielectric Studies of Cu Substituted Barium Hexaferrite Prepared by Sol-Gel Auto Combustion Technique

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.

Effect of sintering temperature on structural property of X-type barium-zinc hexaferrites

X-type Barium-Zinc hexaferrite powder with chemical composition Ba2Zn2Fe28O46 has been prepared using citrate gel auto combustion technique. The combusted powder waspre-heated at 550 °C for 4 hours followed by final calcinations of 1100 °C and 1250 °C for 5 hoursrespectively. Prepared hexaferrite samples were characterizedusingdifferent instrumental techniques such as FTIR and XRD. XRD analysis of the sample calcined at 1250 °C revealed formation of mono phase of X-type hexaferrite; while the sample calcined at 1100 °C shows multiphases of M, W and X-type hexaferrites. FTIR spectra of both samples show stretching of metal-oxide bands.

Influence of various surfactants on magnetic property of cobalt ferrite prepared by Co-precipitation technique

Cobalt Ferrite (CoFe2O4) particles were synthesised using a Co-precipitation method. Influence of three different surfactants i.e. (1) Cationic – CTAB (Cetyl Tri-Methyl Ammonium Bromide), (2) Anionic – SDBS (Sodium Dodecyl Benzene Sulphonate) and (3) Nonionic – Triton X-100, on magnetic property of Cobalt Ferrite were investigated. Magnetic property of Cobalt ferrite powder was studied at room temperature using Vibrating Sample Measurements (VSM) technique under an applied magnetic field of 15kOe. The results show maximum value of saturation magnetization - Ms (81.87 emu/g) for the sample synthesised without surfactant and Coercivity value found maximum (2086 kOe) for the sample synthesized in presence of surfactant SDBS.

Effect of Non-Ionic Surfactant Concentration on Microstructure, Magnetic and Dielectric Properties of Strontium-Copper Hexaferrite Powder

Strontium copper hexaferrite powder with composition Sr2Cu2Fe12O22 was synthesized in presence of a non-ionic surfactant Tween-80 using chemical co-precipitation route. The prepared samples were calcinated at 950 oC for 4 hrs in a furnace and then slowly cooled to room temperature to obtain Sr2Cu2Fe12O22 hexaferrite powder. The effect of surfactant concentration on phase formation, microstructure, magnetic and dielectric properties of Sr2Cu2Fe12O22 were investigated using XRD, SEM, TEM, VSM, dielectric and low field AC susceptibility measurement techniques. The XRD analysis reveals the formation of mixed phases of Y and M type hexaferrites. The synthesized samples exhibited magnetic properties typical for soft magnetic materials, with saturation magnetization typical for Y-type hexaferrites. The dielectric properties were studied within the frequency range 100 HZ to 2 MHz. SEM images show formation of non-uniform, spongy and porous structure. The low field AC susceptibility measurements indicate that formed Sr-Cu hexaferrite powder possesses ferrimagnetic to paramagnetic transition at Curie temperature.

Influence of Ca-Doping on Structural, Magnetic and Dielectric Properties of Ba3Co2-xCaxFe24O41 Hexaferrite Powders

Influence of Ca substitution on structural, magnetic and dielectric properties of Ba3Co2-xCaxFe24O41 (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 Ba3Co2-xCaxFe24O41 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

Effect of Heat Treatment on Structural, Magnetic and Electric Properties of Z-Type Barium Cobalt Hexaferrite Powder

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.