Abstract
In this work, the impact of nonstoichiometric substitution of Fe3+ cations by Ni2+ ones on the structural and magnetic properties of Co0.5Ni0.5+xFe2−xO4 nanoferrites (0.0 ≤ x ≤ 0.4) synthesized by citric autocombustion method has been investigated. The single cubic phase for samples sintered at 600 °C was verified by XRD patterns and FTIR spectra. The crystallite size and microstrain were deduced using Williamson-Hall method, with the former ranging from 55 to 89 nm, in agreement with the TEM microimaging. Hysteresis loops traced via VSM prevailed a regular reduction of the saturation magnetization with Ni2+ substitution. A cation distribution has been suggested for each sample based on the experimental data of XRD, FTIR, and VSM. The suggested cation distribution successfully explained the recorded data of lattice parameter, crystallite size, IR frequencies, magnetization and coercivity. Besides the experimental data, the cation distribution supports the compensation of the nonstoichiometric substitution by the appearance of higher valance states of Fe, Ni, and Co cations.
Highlights
Nanoferrites have been the subject of great interest due to their distinct optical, structural, mechanical and magnetic properties in addition to high chemical and thermal stabilities
We have investigated the effect of the nonstoichiometric substitution of Fe3+ by Ni2+ on the structural and magnetic properties of Co0.5Ni0.5+xFe2 xO4 (0.0 ≤ x ≤ 0.4) nanoferrites synthesized by autocombustion method
Sintering process suppressed the whole magnetic parameters of the samples, which could be attributed to three possible reasons: (1) the formation of higher-valence less-magnetic cations to recover the stoichiometry; (2) cation redistribution, which could be correlated with the IR spectra; and (3) the increase in the crystallite size above the critical size, which is reflected in the significant reduction in coercivity
Summary
Nanoferrites have been the subject of great interest due to their distinct optical, structural, mechanical and magnetic properties in addition to high chemical and thermal stabilities. Structural and magnetic properties of spinel ferrites are strongly dependent on the cations’ occupancy along the A and B sites [17], which is affected by the method of preparation, sintering conditions, chemical composition and types of substitutions. Superexchange interactions are responsible for the ferrimagnetic behavior of spinel ferrites according to the two sub-lattice model [19], where the magnetic spins of the cations at the tetrahedral sites align antiparallelly to those at the octahedral ones. Both coercivity and crystallite size behaved nonmonotonically with Ni substitution To explain such anomalous behaviors, the cation distribution of each single-phase sintered sample has been proposed on the basis of the experimental parameters of lattice parameter, vibrational IR frequencies and magnetization. The matching of such cation distribution with the behavior of the structural and magnetic properties has been analyzed in detail
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