Influence of Rare-Earth on Structural, Magnetic and Electrical Properties of Aluminum Doped Strontium Hexaferrite

Kunwar, Dom Lal. M.S. The University of Memphis. August 2015. Influence of Rare-earth on Structural, Magnetic and Electrical Properties of Aluminum Doped Strontium Hexaferrite. Major Professor: Sanjay R. Mishra, PhD. Among family of ferrites, M-type hexaferrites find host of industrial applications ranging from simple magnets to microwave devices. Improvement in magnetic and dielectric properties of ferrites is a continuous area of interest. The adapted strategies to bring in aforementioned desired improvements are via exploring various synthesis route and doping strategies including viz. magnetic, non-magnetic, and rare-earth atoms in ferrites. In view of the above, the present work studies in detail the effect of co-doping rare-earth (RE: Pr, Sm, and Gd) and aluminum in Sr0.82RE0.18Fe12-xAlxO19 (x=0.0, 0.5, 1.0, 1.5, 2.0) synthesized via autocombustion technique. Detailed synthesis, structural, magnetic, and electrical measurements of samples were performed towards understanding structural-magnetic-electrical property relationship. The variations in physical properties of as synthesized samples were understood in terms of rare-earth ion charge distribution, site occupancy of RE3+ and Al3+ ions, and grain size. The substitution of RE3+-Al3+ brings in grain refinement due to induced lattice strains upon accommodating doped ions. Gd3+-Al3+ displayed smallest crystallite size among all RE3+-Al3+ samples. The Al3+ substitution for Fe3+ brings in significant enhancement in coercivity but reduces magnetization due to magnetic dilution effect. Additional coercivity enhancement was possible with RE3+ doping without affecting the magnetization of samples. This is an important development towards producing high energy magnets. Among all RE3+ doped samples Pr3+ doped samples showed highest Curie temperature, (Tc~465ºC), while Gd3+ doped samples showed little variation in dielectric properties in GHz frequency range. This makes RE3+ doped samples as ideal candidate for high frequency microwave applications. From above observations Pr3+ with oblate charge distribution (negative Stevens constant) was observed to substitute well into the lattice consequently brining in desired improvements in physical properties of Sr0.82RE0.18Fe12-xAlxO19 ferrite

Bacterial inhibition by chitosan coatings loaded with silver-decorated calcium phosphate microspheres

Porous calcium phosphate microspheres have been modified to contain nanoparticles of silver to provide both osteoconductive and antimicrobial components to implant coatings. These microspheres have been mixed with chitosan and bonded to titanium via alkyloxysilane reaction. Silver concentration on calcium phosphate microspheres was varied from 0 to 50% and microspheres were loaded at 30 wt.% within chitosan coatings. Increasing concentrations of silver loaded on calcium phosphate microspheres within the chemically bound coating reduces bacterial viability by up to 90% in both anaerobic and aerobic pathogenic microorganisms, including Staphylococcus aureus, Prevotella denticola, and Porphyromonas gingivalis. This novel coating could reduce the incidence of infection in orthopaedic and dental implant applications