SYNTHESIS AND CHARACTERIZATION OF LITHIUM FERRITE YTTRIUM MANGANITE FERRIMAGNETIC COMPOSITES PREPARED WITH V2O5 Na2SiO3 ADDITIVES

Abstract

newline Lithium and lithium based ferrites with spinel structure that exhibit soft ferrimagnetism possess potential characteristics that can strongly attract the attention of researching. The important properties of this type of ferrites such as high Curie temperature, high and wide range of saturation magnetization, rectangularity of hysteresis loop, low stress sensitivity of remanence, high resistivity, low dielectric and magnetic losses and being a low cost substituted for the expensive garnets for the used in electronic devices make these materials technically promising. In order to enhance their performances, these compounds are often prepared and processed by using a variety of additives with proper control of processing parameters. Lithium ferrites were prepared with different additives having representative formula Li0.5 Fe2.5O4 + (0.1) V2O5 +(x) Na2Sio3, where x= 0.0, 0.05, 0.10, 0.15, 0.20, 0.25. Synthesis was done following ceramic technique using high energy ball milling. The prepared samples were calcined at 650°C for 1h and sintered at 950°C for 1h. The sample having Na2SiO3 concentration, x=0.10 was further studied by sintering at different temperatures viz. 900°C, 950°C, 1000°C, 1050°C and 11000°C for 1h. The structural, electrical and magnetic properties were characterized by various techniques. The study revealed that using the above additives lithium ferrites show improved properties with small amount of Na2SiO3and#8804;0.10wt% additions with 0.1 wt% of V2O5 and sintered at 950°C. Further lithium ferrite-yttrium manganite composites were prepared by adding varying amount of yttrium manganite to lithium ferrite. The composites prepared have the representative formula Li0.5Fe2.5O4 + (0.1wt %) V2O5 +(0.1wt %) Na2SiO3 + (x)YMnO3, with x= (0, 10, 15, 20, 25, 30)wt% which were prepared by adding varying amount of yttrium manganite (YMnO3) to lithium ferrite (Li0.5Fe2.5O4) and sintered at 950°C for 1h. The composites prepared were studied for their structural, microstructural, electrical and magnetic properties. newlineThe XRD patterns revealed that in addition to the reflection peaks corresponding to cubic spinel structure of the ferrite components, a few peaks which are reflections from planes of hexagonal yttrium manganite components have been observed confirming the formation of composites. From the XRD data various structural parameters were evaluated and it has been found that lattice constant and density increased slightly with addition of yttrium manganite while the crystallite size is decreased. The microstructure of the samples was studied from the SEM micrograph taken on the fractured surface of the composites. The grain uniformity seemed improved with YMnO3 addition and#8804;20wt% but decreased more significantly for higher manganite containing composites where pores increase in size and numbers with decreased uniformity in grain distribution. At x=30wt% a distinctive micrographs of large pore size, more in numbers has been found distributed amongst the grain which supports the reduction in the density newlineThe Curie temperature of these samples ranged from 639-634°C. newlineIncorporation of YMnO3 showed a large increase in the D. C. resistivity which may be related with the reduction in the Fe2+ content in the composites prepared. The dielectric properties of these samples were studied using an impedance analyzer. Dielectric constant is highly reduced with the incorporation YMnO3. The variation of dielectric constant and dielectric loss with frequency for the composites showed the dispersion behavior. The temperature variation of dielectric constant and dielectric loss exhibit an increasing trend with the increase of temperature obeying Debye s law. The initial permeability and permeability loss of the samples showed resonance in the range 20-40MHz. The magnetic hysteresis properties were obtained from M-H loop measurements and it is found that the hysteresis parameters such as remanence and coercivity of lithium ferrites were improved with yttrium manganite additions. The results and the mechanism pertaining to the results have been discussed in the thesis. The results of the various studies have been published in reputed journals and presented in conferences and seminars. Future scope of research in this field has been highlighted.