Synthesis and characterization of co-doped SrFe12−x(DyAl)xO19hexaferrite


A series of (Dy-Al)3+co-substituted SrFe12−x(DyAl)xO19(0 ≤ x ≤ 0.9) hexaferrite were prepared via auto-combustion method with subsequent heat treatment in air at 950 °C for 10 h. The phase identification of the powders performed using x-ray diffraction show presence of single phase hexaferrite for x < 0.3 and presence of secondary phase, Fe2O3, for x ≥ 0.3. Lattice parameter of SrFe12−x(DyAl)xO19remains unaffected upon doping mainly due to Fe3+being replaced with a smaller size Al+3and a larger size Dy+3ions than Fe3+. (DyAl)+3substitution modifies saturation magnetization, Ms, and coercivity, Hc. The room temperature Ms value decreased rather slowly with substitution while Hc increased to a maximum value of 5572 Oe at x = 0.9, which is ∼33% increase in coercivity as compare to that of pure Sr-ferrite. The Curie temperature, TC, was observed to decreases upon (DyAl)3+substitution. Dielectric permittivity was improved with (DyAl)3+substitution in 800 MHz to 14 GHz frequency range. The DC electrical resistivity of all samples decreased with temperature showing semiconducting behavior. The room temperature Mossbauer spectral analysis indicate that Al3+prefers 12k, 2a, and Dy3+prefers 4f1 sites. The weighted average hyperfine field and isomer shift decreases with (DyAl)3+content due to magnetic dilution effect and increased charged density per unit cell, respectively. These results indicate that co-doping rare-earth and non-magnetic ion can together maintain high coercivity with fairly high magnetization value of the doped Sr-ferrite.

Publication Title

Journal of Alloys and Compounds