S. R. Sawant

Initial permeability studies on high density CuMgZn ferrites

We have synthesized CuMgZn ferrites by using coprecipitation technique using oxalate precursors. The lattice parameter shows a gradually decreasing trend with increasing Mg2+ content, which is attributed to ionic sizes of Mg2+ and Cu2+ ions. The density of the samples increases with increasing Mg2+ content, which is attributed to smaller ionic size of Mg2+ ions. The Curie temperature does not show appreciable increasing or decreasing trend. The variation in initial permeability (μi) in our compositions is mainly affected by variations of magnetization (Ms) and average particle diameter (D). Also the samples exhibit thermal hysteresis behaviour. The (μi) decreases with increasing Mg2+ content. This is attributed to a lower value of the anisotropy constant (K1) for MgFe2O4 than that for CuFe2O4.

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.

Synthesis of copper–magnesium–zinc ferrites and correlation of magnetic properties with microstructure

A novel route for the preparation of high density, high permeability Cu–Mg–Zn ferrites using oxalate precursors is reported, with various Mg2+ contents represented as Cu(0.5−x)MgxZn0.5Fe2O4 wherein x=0.00, 0.20, 0.25, 0.40. To investigate the ferritization temperature of this system, TG/DTG/DTA studies have been carried out varying from 599 to 743 K with increasing x. X-Ray diffraction (XRD) study revealed that all the samples had a single spinel phase and the cubic lattice parameter ‘a’ decreased with an increase in x. Particle size distribution (PSD) and scanning electron microscopy (SEM) techniques were employed to determine the average particle size and to study the microstructure respectively. Initial permeability of all the samples increased with increase in temperature and Mg2+ content (x≤0.20). It also exhibited a thermal hysteresis effect. The magnetic properties are correlated with high density and grain structure. The magnetic properties of this ferrite system prepared by novel route are superior to those of commercial ETKMG ferrites.

Electrical properties of Si4+ substituted copper ferrite

The electrical resistivity, ϱ, and Seebeck coefficient, α, for the system Cu1+xSixFe2−2xO4 (where x = 0.05, 0.1, 0.15, 0.2 and 0.3) have been studied as a function of temperature. Temperature variation of the resistivity exhibits two breaks. Each break is associated with a change in activation energy. The conduction process at low temperature is governed by the reaction CuA1++ CuA2+→CuA2++ CuA1+. However, at higher temperature, it is due to intersite cation exchange and reoxidation such as CuA2++ FeB3+→ CuB2++ FeA3+. Measurement of the Seebeck coefficient, α, from room temperature to 800 K reveals n-type conduction for the sample with x= 0.05, while the measurements for other samples show p-type conduction for lower temperatures and n-type conduction at higher temperatures. The activation energies in the paramagnetic region are found to be less than those in the ferrimagnetic region.

X-ray and bulk magnetic studies on Li0.5ZnxTixFe2.5−2xO4

Abstract Lattice parameter ‘a’ in the system Li 0.5 (ZnTi) x Fe 2.5−2x O 4 increases monotonically with x, which is attributed to ionic volume differences of the cations involved. The grain size dm increases with the increase of (Zn 2+ Ti 4+ ) concentration to x = 0.3 while for x > 0.3 the grain size shows a decrease with increase of x. The initial permeability first increases gradually and then rapidly with temperature, μi = 0 at T c and its value drops sharply near T c , suggesting single phase territe formation. The addition of Ti 4+ enhances μi values while T c values are lowered. The increase of ui with x is due to a decrease of K 1 The decrease of T c with x is attributed to weakening of A-B interactions due to overall reduction of Fe 3+ ions. From 1 KHz onwards μi is frequency independent while all the samples show large dispersion on the low frequency side. Variation of n B with x reveals that for x B increases with increase of x while for x > 0.3, n B decreases with increase of x. Normalised susceptibility studies show that all the samples contain M.D. particles.

Initial permeability studies on A13+ and Cr3+ substituted Ni–Zn ferrites

The chemical formula of the samples investigated is Ni0.7Zn0.3Alx/CrxFe2-xO4, where x=0.00, 0.05, 0.10, 0.15, 0.20 and 0.25. The samples were obtained by the usual ceramic technology from high-purity oxides. The initial permeability was calculated from the inductance measurements with a torroidal core of 100 turns, using the formula L=0.0046 μiN2h log d2/d1. The initial permeability μi decreases in Ni0.7Zn0.3Alx/CrxFe2-xO4 with increase in Al3+/Cr3+. The decrease in μi is attributed to a decrease of grain size D from 4.9 μm to 4.4 μm with Al3+ and to 1.9 μm with Cr3+ and to variations in the anisotropy constant K1. The main contribution to the variation of permeability with content of Al3+/Cr3+ in the system is the effect each of them has on domain wall motion. The trivalent substituents (Al3+/Cr3+) cause impedance to the domain wall motion, which increases as the content of these ions increases. Al3+ has a stronger effect than Cr3+. The initial permeability components μ′ and μ″ do not exhibit much variation with temperature, except near Tc, where they fall sharply. The maximum of μ″ near Tc has been attributed to a damping effect of domain wall motion.

Magnetic hysteresis in Sn4+ doped Ni-Zn ferrite

Abstract The thermal variation of M r M s and H c reveals that compositions of Ni 0.6 Zn 0.4 Fe 2 O 4 + SnO 2 contain SD + MD, i.e., mixed domain state behaviour. With substitution of Sn 4+ , M r M s decreases while H c increases. Both of these parameters decrease with increasing temperature, which is related to a decrease in the anisotropy constant K 1 . The variation of n B (77 K) with the concentration of Sn 4+ suggests that canted types of spins are favoured with substitution of Sn 4+ .

X-ray and bulk magnetic properties of aluminium substituted ferrites

Abstract The compositions having the general formula Ni 0.55 Zn 0.45 Al t Fe 2- t O 4 and Ni 0.65 Zn 0.35 Al t Fe 2- t O 4 with t = 0.0, 0.1, 0.2, 0.3 have been prepared by the standard ceramic technique and sintered at 1100, 1150, 1200 and 1240°C to attain different microstructures. The lattice parameter a , magnetization M s are seen to decrease with increasing Al 3+ content whereas the coercive force H c shows an increasing trend with Al 3+ content. M s is found to be invariant with the changes in sintering temperature. The coercivity H c and the remanent ratio R = M R / M s are seen to depend on the sintering temperature and hence on the grain size D . The anisotropy field H K A increases with increase of aluminium content. M s and H K A enable calculation of the anisotropy field constant K 1 which decreases with increase of Al 3+ . The compositional, thermal and microstructural variations of hysteresis parameters like M s , H c and R reveal that grains in the compositions investigated are of multidomain (M-D) type. This result is supported by ac susceptibility data.

Effect of sintering conditions and Al3+ addition on wall permeability in Ni1 − xZnxAltFe2 − tO4 ferrites

Ferrite composites having the general formula Ni1 − xZnxAltFe2 − tO4 were prepared using the standard ceramic method. The composites were sintered at four different temperatures to attain different microstructures. The initial permeability μi is found to increase linearly with the grain size for the same composite sintered at different temperatures. Knowledge of the initial permeability μi, magnetization Ms, grain size D, anisotropy field HKA and anisotropy constant K1 led to μi being resolved into wall permeability μW and rotational permeability μr,k. In all the composites the major contribution to μi was due to μw. μi is found to increase with Zn2+ content while it decreases with the addition of Al3+. The initial permeability does not vary significantly with temperature up to the Curie point. Near the Curie point, there is a sharp fall in μi.

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.