Sumitra Phanjoubam

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.

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.

OPTICAL AND STRUCTURAL PROPERTIES OF NANO-SIZED BARIUM STRONTIUM TITANATE (Ba0.6Sr0.4TiO3) THIN FILM

Barium strontium titanate (Ba0.6Sr0.4TiO3) or BST thin films on quartz substrates have been prepared by using a modified sol-gel processing technique. The starting materials are barium 2-ethylhexanoate Ba[CH3(CH2)3CH(C2H5)CO2]2, strontium 2-ethylhexanoate Sr[CH3(CH2)3CH(C2H5)CO2]2 and titanium (IV) isopropoxide Ti[CH3CH3CHO]4. The precursors Ti[CH3CH3CHO]4 except were synthesized in the laboratory. Transparent and crack-free films were fabricated on quartz substrates by spin coating. The as-fired films were found to be amorphous, which crystallized to cubic phase after annealing at 550°C in air for 1 hr. In this paper, we report the structural and optical properties of BST thin films prepared by the modified sol-gel process.

DIELECTRIC PROPERTIES OF Li-Sb FERRITES

Dielectric properties such as dielectric constant (e′) and dielectric loss tangent (tan δ) of Li0.5+xFe2.5-2xSbxO4 ferrites, 0.10≤ x ≤0.30 in steps of 0.05 have been investigated as a function of composition, frequency and temperature. The dielectric constant showed dispersion with frequency in the range of 100 Hz–1 MHz. Peaks were observed in the tan δ versus frequency curves for almost all the samples. The temperature variation of dielectric constant for the different samples was studied at 10 kHz in the temperature range from room temperature to 433 K. Peaks were observed for some of the samples. The peaks were seen to shift towards higher temperature region as the substitution level increases. The mechanisms involved in the processes are discussed in this paper.

EFFECT OF MICROWAVE SINTERING ON THE STRUCTURAL AND ELECTRICAL PROPERTIES OF Li0.51Zn0.2Ti0.2V0.01Fe2.08O4 FERRITE

Effect of microwave sintering on the structural and electrical properties of

Dielectric Properties of Vanadium Substituted Lithium Zinc Titanium Ferrites

{\rm Li}^{+}_{0.51}{\rm Zn}^{2+}_{0.2}{\rm Ti}^{4+}_{0.2}{\rm V}^{5+}_{0.01}{\rm Fe}^{3+}_{2.08}{\rm O}^{2-}_{4}

Hyperfine interaction and cation distribution of the system Ni1+xSnxFe2-2xO4

is studied in comparison with that of conventionally sintered one. The technique is advantageous in terms of significantly reduced size of microwave kilns and rapid heating compared to the cumbersome and slow heating of conventional sintering technology. Microwave sintering produced enhanced densification and much finer microstructures. The DC resistivity is markedly increased. Microwave sintering reduces chances of evaporation of lithium and oxygen during sintering of lithium based ferrites resulting in formation of lesser ferrous ions. This has profound effect on the electrical properties of microwave sintered ferrites. The dielectric constant is significantly reduced possibly due to reduced space charge polarization and the temperature dependence of the dielectric properties are also studied.

Hyperfine interaction studies in the doped lithium ferrite system Li0.5+0.5xCr0.3TixFe2.2-1.5xO4

This paper reports the influence of vanadium substitution on the properties of Li–Zn–Ti ferrite. Samples with compositional formula Li0.5+tZn0.2Ti0.2VtFe2.1-2tO4 (t ranging from 0 to 0.25 in steps of 0.05) were prepared by the conventional sintering technique. XRD analysis confirmed all the samples to be single phase with spinel structure. The lattice constant a density, Curie temperature and Saturation magnetization were measured. The dielectric behaviour was studied as a function of frequency and temperature. The dielectric behaviour showed dispersion with the frequency in the range 100 Hz to 1 MHz. The dielectric constant increases with the increase of temperature for all the samples. The possible mechanisms involved are discussed.

ELECTRICAL CONDUCTION IN SUBSTITUTED Li-FERRITES PREPARED BY MICROWAVE PROCESSING

Abstract Mossbauer investigations were made on the nickel-tin ferrite system with compositional formula Ni1+xSnxFe2-2xO4. The parameter x was varied and single phase compositions could be obtained only for x ⩽ 0.35. Mossbauer studies were carried out at 300 K and 78 K. The spectra for all the samples showed two well defined Zeeman patterns corresponding to A and B sites. The effect of variation of tin concentration on the various hyperfine interactions has been discussed. From the observed experimental results it is concluded that in the cationic distribution of this series all Sn4+ ions occupy octahedral sites.

STRUCTURAL PROPERTIES AND D.C. RESISTIVITY OF Li-Zn-Ti FERRITES

Mossbauer spectra of Li0.5+0.5xCr0.3TixFe2.2-1.5xO4 with x varying from 0.0 to 1.0 in steps of 0.2 have been obtained at 300 K and 78 K. The effect of Ti4+ substitution on the various hyperfine interactions has been discussed. For lower Ti4+ concentrations (0.0 and 0.2) the spectra showed a clear Zeeman pattern whereas, for x>or=0.4, a central quadrupole doublet was present together with the magnetic sextet at both temperatures. The intensity of the doublet was observed to increase with increase in Ti4+ content. This anomalous behaviour of the Mossbauer spectra in the present system has been discussed.