K.V. Siva Kumar

Comparison of initial permeability of MgCuZn ferrites sintered by both conventional and microwave methods

NiCuZn ferrites are widely employed for many electronic applications, but can be replaced by MgCuZn ferrites owing to their superior properties like low magnetostriction, environmental stability, low stress sensitivity and low cost. In view of this, a series of non-stoichiometric MgCuZn ferrites (Mg0.5−xCuxZn0.5Fe1.9O4−δ with x = 0.0, 0.05, 0.10, 0.15, 0.20, 0.25) have been successfully synthesized by both conventional and microwave sintering techniques. The non-stoichiometry was intentionally introduced into the ferrites to ensure high resistivity of the samples. X-ray diffraction patterns confirm the single phase spinel structure in both cases. The elemental composition of these ferrites was analysed by energy-dispersive x-ray spectrometry. The samples sintered by the microwave technique were found to be denser than the conventionally sintered samples. The initial permeability of MgCuZn ferrites was studied with an increase in copper concentration from x = 0.0 to 0.25. The temperature variation of the initial permeability of these samples was carried out from 30u2009°C to 150u2009°C. The results are discussed in the light of microstructure variations of the conventionally and microwave sintered samples. The phenomena involved in microwave sintering are also discussed.

Magnetic properties of Ni-Zn ferrites prepared by microwave sintering method

The effect of zinc ion substitution for nickel on structural and magnetic properties of NiZn ferrites is reported. The spinel ferrite system Ni1-xZnxFe2O4 with xu2009=u20090.2, 0.3, 0.4 and 0.5 was prepared by microwave sintering method. The uniaxially pressed samples were sintered at various temperatures such as 900°C, 1000°C and 1100°C for 30xa0min. X-ray diffraction patterns of the samples indicate the formation of single-phase cubic spinel structure. SEM micrographs show that grain size increases with increasing zinc content and sintering temperature. The elemental composition of these ferrites was analyzed by EDS. Lattice constant increases with increase in zinc content, obeying Vegard’s law. The effect of composition and sintering temperature on initial permeability as the function of frequency and temperature was studied. The initial permeability of NiZn ferrite increases greatly with increasing Zn content and sintering temperature. The dependence of initial permeability with respect to temperature shows the decrease in the Curie point with increase in zinc content, is the normal behavior of ferrites. The relative loss factor

Internal friction and longitudinal modulus behaviour of multiferroic PbZr0.52Ti0.48O3+Ni0.93Co0.02Mn0.05Fe1.95O4−δ particulate composites

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DC conductivity and Seebeck coefficient of nonstoichiometric MgCuZn ferrites

of the order of 10−2 to 10−5 in the frequency range from 100xa0Hz to 1xa0MHz indicates that the prepared ferrites have relatively high purity.

Effect of glass on magnetic properties of microwave-processed MgCuZn nano ferrites

Magnetic nickel ferrite (NiFe2O4) was prepared by sol–gel process and calcined in the 2.45xa0GHz singlemode microwave furnace to synthesize nickel nanopowder. The sol–gel method was used for the processing of the NiFe2O4 powder because of its potential for making fine, pure and homogeneous powders. Sol–gel is a chemical method that has the possibility of synthesizing a reproducible material. Microwave energy is used for the calcining of this powder and the sintering of the NiFe2O4 samples. Its use for calcination has the advantage of reducing the total processing time and the soak temperature. In addition to the above combination of sol–gel and microwave processing yields to nanoscale particles and a more uniform distribution of their sizes. X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy and vibrating sample magnetometer were carried out to investigate structural, elemental, morphological and magnetic aspects of NiFe2O4. The results showed that the mean size and the saturation magnetization of the NiFe2O4 nanoparticles are about 30xa0nm and 55.27xa0emu/g, respectively. This method could be used as an alternative to other chemical methods in order to obtain NiFe2O4 nanoparticles.

Influence of copper substitution on magnetic and electrical properties of MgCuZn ferrite prepared by microwave sintering method

Multiferroic particulate composites with composition xNi0.93Co0.02Mn0.5Fe1.95O4−δ + (1 − x)PbZr0.52Ti0.48O3 where the molar fraction x varies as 0, 0.1, 0.2, 0.3, 0.4 and 0.5 were prepared by the conventional ceramic method. The presence of two phases was confirmed by x-ray diffraction and scanning electron microscopy. The temperature variation of the longitudinal modulus (L) and the internal friction (Q−1) of these particulate composites at 104.387 kHz was studied in the wide temperature range 30–420 °C. The temperature variation of the longitudinal modulus (L) in each composition of these particulate composites showed two abrupt minima. One minimum coincided with the ferroelectric–paraelectric Curie transition temperature (θE) and the other with the ferrimagnetic–paramagnetic Curie transition (θM) temperature. The internal friction (Q−1) measurements also showed two sharp peaks in each composition corresponding to those temperatures where the minima were noticed in the temperature variation of the longitudinal modulus behaviour. The Curie transition temperature of pure ferrite was found to be 560 °C. Addition of 10% of ferrite to ferroelectric in a magnetoelectric (ME) composite resulted in a 360 °C fall in θM and with a further increase in ferrite content the θM variation was found to be very nominal. However, no significant ferroelectric Curie transition temperature shift could be noticed. This behaviour is explained in the light of structural phase transitions in these multiferroic particulate composites. These ME composites were prepared with a view to using them as ME sensors and transducers.

STRUCTURAL, MAGNETIC AND ELECTRICAL PROPERTIES OF NICUZN FERRITES PREPARED BY MICROWAVE SINTERING METHOD SUITABLE FOR MLCI APPLICATIONS

The xNi0.83Co0.15Cu0.02Fe1.9O4−δ (NCCF) + (1−x)PbZr0.52Ti0.48O3 (PZT) particulate magneto ferroelectric composites with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 mole fraction were prepared by conventional ceramic double sintering method. The presence of two phases (perovskite structure of ferroelectric phase and spinal structure of ferromagnetic phase) was confirmed by X-ray diffraction. The magnetoelectric (ME) property of the particulate composites was determined at room temperature as a function of intensity of magnetic field. The temperature variation of the longitudinal modulus (L) and the internal friction (Q−1) of these particulate composites at 104.3 kHz was studied in the wide temperature range 30–420 °C. The temperature variation of the longitudinal modulus in each composition of these particulate composites showed two abrupt minima. One minimum coincided with the ferroelectric — paraelectric Curie transition temperature (θE) and the other with the ferromagnetic-paramagnetic Curie transition temperature (θM). The internal friction measurement also showed two sharp peaks in each composition corresponding to those temperatures where the minima were noticed in the temperature variation of the longitudinal modulus behaviour.

Enhanced mangnetoelectric voltage in multiferroic particulate Ni0.83Co0.15Cu0.02Fe1.9O4−δ/PbZr0.52Ti0.48O3 composites – dielectric, piezoelectric and magnetic properties

Abstract Nonstoichiometric series of Mg0.5−xCuxZn0.5Fe1.9O4−δ where x = 0.0, 0.1, 0.15, 0.2 and 0.25 has been synthesized by conventional solid state reaction route. The single phase spinel structure of the double sintered ferrites was confirmed by X-ray diffraction patterns (XRD). The ferrite series was studied in terms of DC electrical conductivity and thermoelectric power in the temperature ranging from room temperature to 300 °C and 400 °C, respectively. It was observed that DC electrical conductivity and Seebeck coefficient α decreased with the increase in x. DC electrical conductivity was found to decrease by about 4 orders. All the compositions showed a negative Seebeck coefficient exhibiting n-type semiconducting nature. From the above experimental results, activation energy and mobility of all the samples were estimated. Small polaron hopping conduction mechanism was suggested for the series of ferrites. Owing to their low conductivity the nonstoichiometric MgCuZn ferrites are the best materials for transformer core and high definition television deflection yokes.