S. S. Suryavanshi

D.C. conductivity and dielectric behavior of Ti4+ substituted Mg-Zn ferrites

Abstract The variation of d.c. resistivity (ρ) and activation energy (ΔE) with Ti4+ concentration show similar behaviour. The gradual change of ρ for low Ti4+ concentration is attributed to the occupation of the A sites by Ti4+ ions and additional Fe3+ ions becoming available to the B sites. The linear increase of resistivity for higher Ti4+ concentration is attributed to an overall decrease Fe3+ ions on Ti4+ substitution. Dispersion of the dielectric constant is related to the Verwey conduction mechanism. Peaks have been observed in the variation of loss tangent (tan δ) with Ti4+ concentration. These peaks shift to the low frequency side on increasing the content of Ti4+. The jump frequencies are found to be in the range 70–120 kHz. All the samples exhibit space charge polarization due to an inhomogeneous dielectric structure. It is concluded that the addition of Ti4+ obstructs the flow of space charge.

Conduction mechanism in Sn4+ substituted copper ferrite

Thermoelectric power (α) and electrical resistivity (ρ) are reported for the system Cu1+xSnxFe2−2xO4 (wherex=0·05, 0·1, 0·15, 0·2 and 0·3) from room temperature to 800 K. The compositions withx=0·05 and 0·2 exhibitn-type conduction while the compositions withx=0·1 and 0·15 showp- ton-type conduction change after 423 K. The conduction at low temperature (i.e. < 400 K) is due to impurities, while at higher temperature (i.e. > 400 K), it is due to polaron. Hopping conduction phenomenon for the present system has been explained on the basis of localized model of electrons. Additional localization may arise due to Sn4+ + Fe2+ stable pairs at B-site and Cu1+ + Fe3+ pair at A-site.

XRD and magnetic studies on Ti-substituted MgZn ferrites

Abstract The ferrites of the compositions Zn x Mg (1−x)+t Ti t Fe 2−2t O 4 are prepared by a standard ceramic method. The spinel structure is confirmed for these ferrites, however impurity lines for higher concentration of Mg have been observed. Compositional variation of lattice parameter has shown non linearity on addition of zinc which is explained by the combined effect of cation size on repulsion parameter and of the A-site charge on Madelung constant. Temperature variation of susceptibility has shown peaks which gradually disappear on addition of Zn. This is explained on SD-SP transition. The peak temperatures and Curie temperatures from X-T variation and obtained experimentally decrease on addition of Zn which is attributed to reduction of A-B interactions. The magnetisation studies have shown Neels two sublattice and three sublattice models applicable to the system. The values of M:M s and H c decrease on addition of Zn which is attributed to SD-MD transformation.

Temperature and frequency dependence of initial permeability in Zr4+-substituted CuZn ferrites

Abstract Temperature and frequency variation of initial permeability reveal a decrease in initial permeability with the addition of Zr4+ ions. With increasing temperature, the permeability increases and then falls sharply near TC. The maximum variation in the permeability is explained by the presence of Fe 3+ Fe 2+ and Cu 2+ Cu + ions , a decrease in density and a change of microstructure. All the samples show a frequency-independent permeability variation. It is concluded that the addition of Zr4+ locks the domain wall motion.

Wall permeability studies on Ti4+ doped Ni-Zn ferrite

Compositions of Ni0.6Zn0.4Fe2O4 with variable weight percent addition of TiO2 exhibit wall permeability dominance. With increase of TiO2 concentration the permeability decreases which is related to the impedance to the domain wall motion. The permeability obeys the Globus model with evident wall bulging effect.

Relaxation time studies on Ni0.7Zn0.3AlxFe2 − xO4 and Ni0.7Zn0.3CrxFe2 − xO4

The effect of substitutions of Al3+ and Cr3+ on τm in Ni-Zn ferrites prepared using usual ceramic technology has been investigated. The relaxation time τm for the system of ferrites Ni0.7Zn0.3AlxFe2−xO4 and Ni0.7Zn0.3CrxFe2−xO4 increases with the increase in the Al3+ and Cr3+ content. This is attributed to an increase in the resistivity. An increase in τm with Al3+ and Cr3+ suggests that the response of the material to the field variation is slowed down, i.e. these substitutions cause hinderance to the domain wall motion. From the observation that the rate of change of τm with Al3+ substitutions is greater than that with Cr3+ substitutions, it can be concluded that Al3+ causes more hinderance to the domain wall motion than Cr3+ ions.

XRD and bulk magnetic studies on Ni-Cd and Ti doped Ni-Cd ferrites

For the ferrites NixCd1−xFe2O4 (x=0.3, 0.4,⋯1) the lattice parameter, grain size, electrical resistivity, initial permeability, Curie temperature and squareness of the magnetization curve were measured. The results are discussed in terms of the model of the canted spin structure taking into account the domain structure of the polycrystalline ferrite.

Microstructure studies on Ti4+- and Zr4+-substituted Li-Zn ferrites

XRD and microstructure studies were carried out on Ti4+ and Zr4+-substituted Li-Zn ferrites prepared by standard ceramic technique. All the ferrite compositions exhibit single phase formation. The lattice parametera increases linearly with the content of Zn2+Zr4+ and Zn2+Ti4+, which is attributed to the ionic volumes of the cations involved. With substitution by Zr4+ the average size decreases, while with substitution by Ti4+ the grain size increases. In both the series grain size varies with the composition. Excess substitution of Zr4+ (x>0·4) leads to the formation of secondary images and discontinuous grain growth. Both Zr4+ and Ti4+ compositions obey Kurtz theory.