Magnetic and Mössbauer studies of hot-pressed MnZnNi ferrites (abstract)

Abstract

Hot-pressed MnZn ferrites are extensively used for magnetic recording applications. The present work investigates the magnetic properties of MnZnNi ferrites by using the Mössbauer spectroscopy and taking bulk magnetic measurements. Ferrites of the composition Mn0.6Zn0.4−xNixFe2O4 (0≤x≤0.4) have been prepared by uniaxial hot pressing technique. The final sintering was performed at 1250 °C for 3 h under a pressure of 35 MPa. The samples exhibit high density (porosity <0.1%) nearly uniform grain size (average grain size=0.01 mm approx.), and large Vickers’ hardness (650 approx.). The variations of initial permeability, saturation magnetization, Curie temperature, and coercive field are studied by changing Ni2+ content. The initial permeability increases slightly for x≤0.05, attains a maximum value of 5660, and decreases continuously for x≳0.05. The saturation magnetization increases for x≤0.25 and decreases for x≳0.25. The maximum saturation magnetization obtained for x=0.25 is 4825 G. The Curie temperature increases markedly from 431 to 682 K with increasing Ni2+ content. The coercive field decreases slightly for x≤0.05, becomes as low as 0.09 Oe, and increases almost linearly thereafter. The results are explained on the basis of sublattice magnetizations, stren of AB exchange interactions and change in magnetocrystalline anisotropy constant. The Mössbauer studies reveal the well-defined hyperfine spectra for Ni2+-substituted samples. The isomer shift remains almost unaffected by Ni2+ substitution, while the quadrupole splitting is observed to be negligible for all the samples. The hyperfine field decreases continuously as x increases from 0 to 0.4. The occupancy ratio of Fe3+ ions on octahedral to tetrahedral sites yields a cation distribution which conforms with the bulk magnetic measurements. The MnZnNi ferrite compositions with x ranging from 0.05 to 0.10 exhibit properties which make them suitable materials for recording head applications.