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Pure phase exchange coupled nanocomposites of magnetically hard-soft oxides, (hard) SrFe12-yAlyO19 -(soft) x Wt.% Ni0.5Zn0.5Fe2O4 were prepared via one-pot autocombustion method. The hard-phase magnetic anisotropy was systematically varied via Al3+ doping and magnetic properties of the nanocomposites were assessed as a function of magnetic soft-phase content in the nanocomposite. As synthesized, ferrites were assessed for phase composition, crystallinity, and magnetic properties by using XRD and VSM respectively. Exchange coupling behavior was observed in nanocomposites for all soft phase content in the low field region up to 1200 Oe. Also, exchange coupling was observed to weaken with increase in Al3+ content in the hard phase of the composite. As a result of hard-soft exchange coupling, the saturation magnetization, reduced remanence, and Curie temperature were observed to be higher than those of pure SrFe12O19 hexaferrite. The present study is novel in its approach of tuning magnetic parameters of exchange-spring nanocomposites via systematically controlling magnetic parameters of the hard phase and content of the soft phase. [ABSTRACT FROM AUTHOR]

A series of (Dy-Al) 3+ co-substituted SrFe 12−x (DyAl) x O 19 (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, Fe 2 O 3 , for x ≥ 0.3. Lattice parameter of SrFe 12−x (DyAl) x O 19 remains unaffected upon doping mainly due to Fe 3+ being replaced with a smaller size Al +3 and a larger size Dy +3 ions than Fe 3+ . (DyAl) +3 substitution 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, T C , 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 Al 3+ prefers 12 k , 2a, and Dy 3+ prefers 4 f1 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. [ABSTRACT FROM AUTHOR]

A series of Al 3+ substituted CoFe 2-x Al x O 4 ( x = 0.0 to 0.9) ferrite nanoparticles were synthesized via autocombustion method. XRD data show that all the samples exhibit single phase cubic spinel structure where the lattice parameter was observed to decrease linearly with increasing Al 3+ content. Structurally Al 3+ doping was observed to bring in grain refinement and increase dislocation density in CoFe 2-x Al x O 4 . The magnetic parameters namely saturation magnetization, M S , coercive field, H C , and remanent magnetization, M r vary significantly with Al 3+ doping. The Al 3+ doping resulted in reduction in Ms and Hc due to magnetic dilution effect and reduction in anisotropy constant K1 , respectively. Room temperature Mössbauer spectra were analyzed to extract cation distribution and hyperfine parameters. The hyperfine magnetic field decreases at both tetrahedral (A) and octahedral (B) interstitial sites with the increase in Al 3+ content. The Mössbauer spectral analysis reveals that Al 3+ has preference for the tetrahedral A site and Co 2+ prefers B sites. [ABSTRACT FROM AUTHOR]