| ('57)Fe Mossbauer resonance has been used to investigate the influence of chemical and structural inhomogeneities on the physical properties of two important classes of magnetic oxides. SrFe(,12)O(,19), the strontium analog of the class of magnetic oxides with the magneto-plumbite structure is known to exhibit superior magnetic properties if the initial reaction mixture contains excess Sr, i.e. is nonstoichiometric. SrFe(,12)O(,19) has been investigated to determine the mechanism by which excess Sr influences the magnetic properties. It has been determined that a Sr-rich intermediate phase is essential to the formation of the SrFe(,12)O(,19), and that nonstoichiometric hexaferrites contain a complex second phase with a composition different from that of the intermediate phases involved in the formation of SrFe(,12)O(,19). In highly nonstoichiometric compositions, three phases are observed to coexist. Although, the precise composition of the phase present in the Sr-rich hexaferrites has not been determined, it has been shown that the relative magnetizations of the different magnetic sublattices in SrFe(,12)O(,19) are significantly influenced by small deviations of the SrO:Fe(,2)O(,3) ratio from the stoichiometric value.;The second class of materials investigated is spinel ferrites with chemical compositions Mn(,1-x)Zn(,x)Fe(,2)O(,4) exhibiting technologically important switching properties. Naturally occurring Mn-Zn spinel ferrites which have obtained a closer approach to thermodynamic equilibrium than is possible in a laboratory environment, were investigated. It had been theorized that the switching properties of these materials is significantly influenced by localized structural and chemical inhomogeneities. Localized chemical and structural inhomogeneities consistent with those, postulated to influence the switching properties, have been confirmed in certain members of the suite of natural Mn-Zn ferrites. |
