Pran Kishan

Study of magnetization and crystallization in sputter deposited LiZn ferrite thin films

LiZn ferrite films of composition Li00.5−x/2Mn0.1ZnxFe2.35−x/2O4 with x=0.32 were rf sputter deposited on fused quartz substrates at ambient temperature. The as-deposited films were found by x-ray diffraction to be amorphous but magnetic, and showed large high field susceptibility. The films were studied after they were annealed at various temperatures up to 850 °C. It was observed that the films crystallize upon annealing and the value of the saturation magnetization increases with annealing temperature. The high field susceptibility, on the other hand, decreases with increasing anneal temperature. The measured ferromagnetic resonance spectra of these films indicated that the films consist of at least two different magnetic materials. A significant portion in the film crystallizes and the value of saturation magnetization of this portion tends to the bulk value as annealing temperature is increased. However, a small portion of the film remains in a highly defective state all through, even up to annealing...

Hyperfine interactions and magnetic studies of Li-Mg ferrites

Abstract The paper describes the investigations carried out on a series of mixed LiMg ferrite compositions represented by the formula Li0.5-0.5xMgxFe2.5-0.5xO4. A systematic studies of the magnetic properties and the Mossbauer parameters e.g. isomer shift, quadrupole splitting and nuclear magnetic fields at tetrahedral (A) and octahedral (B) sites have been carried out. The observed experimental results have been discussed in terms of cationic distribution and exchange interaction. It is inferred that the substituent (Mg2+) ions in Li0.5Fe2.5O4 occupy both sites of the spinel structure.

Electrical conductivity of NiZn ferrites doped with Ti4+ ions

Abstract The d.c. resistivity ρ of the polycrystalline solid solutions Zn0.25Ni0.75 + t−TitFe2−2tO4 was measured as a function of titanium content and temperature. The electrical conduction in these ferrites is explained on the basis of the hopping mechanism. The composition dependence of the resistivity is explained in terms of the cation distribution. The activation energy of each sample is calculated from the plots of log ρ versus 10 3 T which are almost linear.

Electrical conduction and dielectric behaviour in zinc-substituted lithium ferrites

Abstract Zinc-substituted lithium ferrites Li 0.5− z 2 Zn z Fe 2.5− z 2 O 4 with z varying from 0 to 0.7 were prepared. Small amounts of bismuth oxide were used to reduce the sintering temperature. In dense materials prepared in this way Bi 2 O 3 segregates at grain boundaries and the grains consist of only the basic ferrite. Electrical properties such as the resistivity, the dielectric constant and the loss factor were measured over a wide frequency range. The parameters obtained at direct current and high frequencies were used to explain the properties of the materials in terms of a two-layer model. In samples with z > 0.4 the observed behaviour was attributed to cluster formation at the grain boundaries.

Dielectric and magnetic properties of polycrystalline cobalt‐substituted LiTi ferrites

The electric, dielectric permittivity, loss tangent, microwave power absorption, and hysteresis loop parameters were studied on a series of cobalt‐substituted lithium titanium ferrites. The experimental results indicate that cobalt substitution affect all these parameters. The observed dispersion in conductivity and dielectric permittivity with frequency and temperature are in accordance with Maxwell–Wagner model while the microwave and hysteresis loop properties can be interpreted with the help of Dionne’s exchange isolation model.

Effect of Ti4+ substitution on the hyperfine interactions in LiZn ferrites

Abstract 57 Fe Mossbauer investigations were made on the system Li 0.35+0.5 t Zn 0.3 Ti t Fe 2.35−1.5 t O 4 (0.0≤ t ≤1.2) at 300 K and 77 K. The effect of variation of Ti concentration on the various hyperfine interactions have been discussed. It is observed that for t ≤0.6 the Mossbauer spectra show well defined Zeeman pattern. The spectra for t = 0.8 is relaxed while for t ≥1.0 there is the existence of a central doublet along with the relaxed magnetic sextet. This anomalous behaviour of the Mossbauer spectra at high diamagnetic substitution and the origin of the central doublet have been discussed.

Cation distribution in germanium-substituted magnesium ferrites

Magnetic properties of a series of tetravalent germanium substituted magnesium ferrites with the compositional formula Mg1+xGexFe2−2xO4. (x = 0, 0.1, 0.2, 0.3 and 0.4) are reported. The lattice constant was found to decrease with x. The observed variation of coercive force and remanence ratio with temperature for all the samples are consistent with the single domain behaviour of the material. Magnetisation measurements were carried out from 100°K to the Curie temperatures of the respective samples. O°K magnetisation values were obtained by extrapolating the magnetisation vs temperature plots. Taking into consideration the strong affinity of Ge4+ ions for A-site occupancy and the 0°K magnetisation data, the cation distribution for this series of compositions has been worked out.

Elastic behaviour of Zn-substituted LiMg and LiMgTi ferrites

Abstract Two series of Zn-substituted LiMg and LiMgTi ferrites were prepared by the solid state reaction method with a view to investigate their elastic behaviour. The elasticity studies were undertaken by measuring the ultrasonic velocities by adopting the pulse transmission technique. As the materials under investigation are porous, the experimentally obtained elastic moduli such as Youngs moduli, rigidity moduli, Poissons ratio have been corrected to zero porosity using Ledbetter and Dattas formulae. It has been observed that all the elastic moduli decrease continuously with increasing dopants concentration. Using the experimental data, other important elasticity parameters such as the Debye temperature, V l /ρ and V s / ρ have also been evaluated and their variation with dopants concentration has been explained qualitatively.

Effect of MgTi and ZnTi substitutions on electrical and magnetic properties of Li ferrite

Abstract Simultaneous substitutions of varying amounts of Zn2+ Ti4+ and Mg2+ Ti4+ have been incorporated into Li ferrite. A comparative study of the magnetic and electrical properties of the two series has been carried out. Diverse trends of variation of some of the magnetic parameters have been observed for the two sets of ferrite samples. The observed behaviour is explained on the basis of the site preference of substituent ions and their effect on the microstructural developments in the material.

Thermogravimetric and differential thermal studies of YBaCuoxide system

Abstract Thermogravimetric and differential thermal studies of YBaCuOxide system were carried out up to 1000°C. From the TG and DT plots for the samples of individual raw materials, mixed raw materials, prefired material in oxygen atmosphere and heating of the superconducting phase, it is concluded that the oxides react to form the pervoskite phase at around 965°C. The observed gain in weight due to oxidation during sintering operation and loss occuring on heating of the sintered sample agree with the expected additional oxygen content.