Elastic behaviour and internal friction of polycrystalline magnesium ferrite

Abstract

The magnetic, dielectric and electrical properties of ferrites have been investigated in great detail. The magnetic properties [1] have been studied thoroughly in the neighbourhood of the Curie point and these studies established that the magnetic behaviour of ferrites is similar to that of metallic ferromagnetic substances. However, there is meagre information available on the various "non-magnetic" properties such as thermal expansion, specific heat, elasticity, etc., in the neighbourhood of the Curie point in the case of ferrimagnetic materials. A detailed study of the elastic behaviour is of particular significance in the theory of solids in understanding the nature of the interatomic and interionic forces in them. It is thus a matter of great interest to study the elastic behaviour of ferrites in the neighbourhood of the Curie point, where the energy of the spontaneous magnetization disappears. As such we have undertaken a study of the dependence of the elastic moduli of polycrystaUine magnesium ferrite on temperature and magnetic field in the neighbourhood of Curie temperature. Internal friction is another important property, which is closely related to the elastic behaviour. As such the internal friction of the ferrites is also studied. The specimens of magnesium ferrite were prepared by the double sintering method. The final sintering was done between 1250 and 1350 ° C in an air atmosphere. The ferrite specimens were analysed from the results of X-ray diffraction studies and are found to be monophasic. The bulk densities of the samples were found to be about 90% to 95% of the corresponding X-ray densities. The natural longitudinal and transverse frequencies of the specimens as a function of temperature and magnetic field have been determined by the three-component oscillator method [2]. The internal friction measurements were also carried out using the same composite oscillator method, as was used for the elastic moduti measurements. The internal friction values are calculated after noting the width of the resonance curve, when the specimen vibrates in resonance with transducer. The length and density of the ferrite specimens at different temperatures (t) have been calculated using the thermal expansion (a) determined in this laboratory. The relevant equation used for magnesium ferrite is,