B.K. Chougule

Microstructure, frequency and temperature-dependent dielectric properties of cobalt-substituted lithium ferrites

Abstract Ferrites with the general formula Li 0.5− x /2 Co x Fe 2.5− x /2 O 4 (where x =0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7) were prepared by the standard ceramic method. AC resistivity ( ρ AC ), dielectric constant ( e ′) and dielectric loss tangent (tan δ) were measured as a function of frequency and temperature. The compositional variations of ρ DC and e ′ with x show inverse trends with each other. The dielectric constant increases slowly from 0 to 450 with temperature in the beginning and sharply after 200°C. The e ′ and ρ DC show a decrease with increase in frequency for all the samples. The variation of tan δ with frequency shows cusps for all the samples except for x =0.5. These variations have been explained on the basis of Koops phenomenological theory, concentration of Fe 2+ and Fe 3+ ions on octahedral site and hopping frequency of electrons between Fe 2+ and Fe 3+ .

Infrared spectral studies of Zn-substituted Li-Mg ferrites

Abstract The infrared spectra of Zn-substituted Li–Mg ferrites, having the general formula Li x Mg 0.4 Zn 0.6−2 x Fe 2+ x O 4 (where x =0, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.3), have been analyzed in the frequency range 200–800 cm −1 . The ferrites were prepared by standard double sintering ceramic method and the single-phase formation was confirmed by X-ray diffraction studies. The IR spectra show two fundamental absorption bands ν 1 and ν 2 in the range 600–400 cm −1 , corresponding tetrahedral and octahedral complexes, respectively. The bands ν 1 and ν 2 are found to shift gradually towards the lower frequency side with addition of Zn, which have been attributed to the increase in the lattice parameter. The bands do not show any sign of splitting indicating no excess formation of Fe 2+ ions.

Microstructure and permeability studies of mixed Li-Cd ferrites

Abstract Some microstructure-related properties of Li0.5−x/2CdxFe2.5−x/2O4 ferrites have been reported. SEM micrographs show an interesting grain growth mechanism. Grain size increases up to x=0.3 and then decreases very slowly beyond it. Saturation magnetisation also follows the same trend. But initial permeability shows continuous increase up to x=0.6 and is explained on the basis of non-magnetic grain-boundary model. The variation of initial permeability and AC susceptibility with temperature shows normal ferrimagnetic behaviour. The Curie temperature decreases continuously with x, which is attributed to the decrease in the strength of the A–B interaction.

Infrared studies of some mixed Li–Co ferrites

Abstract The infrared spectra of Li–Co mixed ferrites with the general formula Li0.5−x/2CoxFe2.5−x/2O4 (where x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7) have been analyzed in the frequency range 200–800 cm−1. The single phase formation of ferrites was confirmed by X-ray diffraction studies. The IR spectra revealed four absorption bands for the sample x=0.1 and x=0.2. The sample with x=0.3 and 0.4 exhibit three absorption bands and the samples with x>0.4 show two prominent absorption bands. The IR bands are attributed to the fundamental vibrational modes of tetrahedral and octahedral complexes of the unit cell. The IR band due to tetrahedral complexes is found to be shifted slightly towards high frequency side where as that due to octahedral complexes is found to shift towards lower frequency side. The bands do not show splitting indicating no excess formation of Fe2+ ions.

Electrical properties and magnetoelectric effect measurement in (x)Ni0.8Cu0.2Fe2O4 + (1 − x)Ba0.9Pb0.1Ti0.9Zr0.1O3 composites

Composites with compositions (x)Ni0.8Cu0.2Fe2O4 + (1 − x)Ba0.9Pb0.1Ti0.9Zr0.1O3, in which x varies as 0, 0.15, 0.30, 0.45 and 1 mol%, were prepared by a standard ceramic technique. X-ray diffraction was used to carry out the structural analysis. The microstructural analysis was carried out by scanning electron microscopy. The variation in dc resistivity with temperature was studied in the temperature range 300–773 K. The variation of dc resistivity with temperature shows a semiconducting behavior. From ac conductivity measurements in the frequency range 100 Hz to 1 MHz it is concluded that the conduction in the present composites is due to a small polaron hopping. The variations in dielectric constant and loss tangent were also studied. The magnetoelectric effect (ME) (dE/dH)H was measured as a function of intensity of the dc magnetic field. The maximum value of ME conversion factor was observed to be 431 µV cm−1 Oe−1 for the 15%Ni0.8Cu0.2Fe2O4+85%Ba0.9Pb0.1Ti0.9Zr0.1O3 composite. The ME coefficient has been explained in terms of ferrite–ferroelectric content.

Some ac electrical properties of Li–Mg ferrites

Abstract The ac resistivity (ρac), dielectric constant (ϵ′), dielectric loss tangent (tan δ) and initial permeability (μi) of mixed Li0.5−x/2MgxFe2.5−x/2O4 (where x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) ferrite system were measured at room temperature as a function of frequency in the range from 1 kHz to 1 MHz. The resistivity of all the samples decreased with increase in frequency, indicating that the samples exhibited normal ferrimagnetic behavior. The compositional variation of resistivity and dielectric constant indicated the inverse trends of each other. The sample with x = 0.3 showed the lowest resistivity and the highest dielectric constant. The dielectric loss tangent showed maxima at 3 kHz for x = 0.2 samples and at 15–20 kHz for x = 0.3 and 0.4 samples. All of the variations are explained on the basis of Fe2+/Fe3+ ion concentration on octahedral sites as well as the electronic hopping frequency between Fe2+ ⇔ Fe3+ ions.

Magnetic properties of mixed Li–Ni–Cd ferrites

Abstract The magnetic properties of mixed Li0.5Ni0.75−x/2Cdx/2Fe2O4 (where x=0, 0.1, 0.3, 0.5, 0.7 and 0.9) ferrites have been reported. The lattice parameter increases linearly with Cd content, which is attributed to ionic size differences of the cations involved. The saturation magnetization increases with increase in cadmium content up to 0.25 and then it decreases with further addition of Cd. The decrease in saturation magnetization (Ms) above Cd=0.25 is explained on the basis of canted spin model. The a.c. susceptibility measurements show presence of MD particles in the samples. The initial permeability is found to increase monotonically with cadmium content. It is observed that μi increases gradually with temperature and then it drops to zero near Curie temperature (Tc). The continuous decrease of Curie temperature (Tc) with Cd2+ content is attributed to the dilution of A–B interaction.

Cadmium substituted high permeability lithium ferrite

Polycrystalline Li0.5-x/2CdxFe2.5-x/22O4 ferrites wherex = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 were prepared by a double sintering ceramic technique and characterized by X-ray diffraction and scanning electron microscopy (SEM). The lattice parameter is found to increase monotonically with the cadmium content. It is explained in terms of the sizes of component ions. The grain size of the samples increases up tox = 0.3 and then it decreases for higher values ofx. A similar trend is observed in the variation of Ms with Cd2+ content. The initial permeability (μi) is however found to increase continuously withx. The increase in μi is attributed to decrease of anisotropy constant K1 and higher grain size of the samples.

Susceptibility and magnetization studies of Gd3+ substituted Mg-Cd ferrites

Studies on lattice parameters, magnetization and ac susceptibility measurements for the ferrite system CdxMg1−xGdyFe2−yO4 (withx = 0·2, 0·3, 0·4 andy = 0·1, 0·2, 0·3, 0·4) are presented. The ac susceptibility was measured from room temperature to 800K at a constant magnetic field of 7 oersted.Xac vsT variations show that all the samples contain predominantly multidomain (MD) particles. Magnetization measurements of the system indicate that as the Cd2+ content increases magnetization increases while the addition of Gd3+ reduces the magnetization. The observations further indicate the existence of Y-K type of magnetic ordering in the system.

Effect of sintering on the magnetization behaviour of Mg x Zn(1 −x)Fe2O4 system

Magnesium zinc ferrites with the general formula MgxZn(1 −x)Fe2O4 were prepared by the standard ceramic technology route involving double sintering. X-ray analysis was carried out to confirm the single-phase formation as well as to calculate the lattice parameters. Two sets of samples were prepared by sintering the samples at 1100°C for 15 and 30 h respectively. The high-field loop tracer was used to measure the hysteresis parameters. It is observed that the sintering conditions effectively modify the magnetization characteristics of these ferrites.