Electrical and magnetic properties of nickle-magnesium ferrites

Abstract

Thi8 thesis describes thc cxperimental mvestigation ofthc structural, magnetic and electrical propertIes ofNil_xMgxFe,O. with x=O.l, 0.4, 0.&, 0,8, and 1.0. The samples were prepared by using the standard double sinlering ceramic technique sintered at 1250"C. The structural characterization of the studied samples such as phase, lattice parameter, density, porosity has been performed by X-ray diffraction. Magnetic propenie8 such as initial permcability, re1atnre quality factor, imaginary part of complcx permeabdily, Curie temperature, saturation magnetization have been measured as a runetion of field, temperature and frequency using Vibrating Sample Magnetometer (VSM) and Impedance Analyzcr. Eleetncal properties such as DC and AC electrical resislivity, dielectric constant as a function of composition and frequency have been studied. X-ray diffraction resulls confimled the single phase spinel structures 01' all the studied samples. The lattice parameter increases linearly with increasing ofMg content obcying Vegard's law, This is attributcd to the substitution of larger Mg"t O,72(A) for smaller Ni2+ 0,69(A) ions at B site and also a small fraction (about 10%) of Fel> ions migratcd trom A sile to B site. Thc theorctical and bulk density of the samples decreasc monotomcally with increasing of Mg contcnt which may be attributed lo much lower density, 1.74 glcml of Mg than that ofNI having high density or 8.91 gm/cm1. Porosity of the studied samples has been found to decrease with increasing of Mg contcnt. The decrease of porosity may be ascribed as thc reduced of intragranular porosity. The magnetization or the samples decreases with increasing Mg content. The behaviour of the concentration dependence or magnetization is discussed on the basis of cation distribution. Experimental magnetic moment is slightly les8 than the theorctieal magnetic moment. Curie temperature (Td has been determined rrom the temperature dependence of initial pemleabilily at constant frequency. It is found that T, decreases linearly with increasing of Mg due to the weakening of A-B exchange interaction. From the frequency dependence ofpermeabl1ily spectra, it is noticed that all the samples are ahnost independent of frequency up to 10 MHz. It is observed that permeabllity decreases with increasing of Mg content which is ascribed to the decrease of densily and saturation magnetization. The relative quality factor decreases with increasing of Mg content (except for x = 0.4). The rrequency corresponding to maximum of relative quality factor shifts to higher value with the increase of Mg content. Imaginary part of permeability increases above 10 MHz frequency due to increase of magnetic losses. Room tempendure DC resistivity decreases with increasing Mg content and AC rcsislivlty initially decreases rapidly "jth frequency to a minimum value at about 2 MHz and then again resistivity increases almost linearly. Decrease of AC resistivity has been explained by hopping mecJmnism. Frequency dependence of dielectric constant shows the normal behaviour of the ferrite materials which can be explained by the interfacial polarization as predicted by Maxwe1l3nd Wagner.