The effects of lanthanum ions substitution on properties and effective absorption bandwidth (EAB) of zinc ferrite

Abstract

A comprehensive study was conducted to examine the effect of lanthanum (La3+) ions substitution on zinc ferrite crystallography parameters, microstructure, and related physical properties. In this work, ZnLaxFe(2-x)O4 (0.01 ≤ x ≤ 0.04) compositional series were prepared by co-precipitation method. Rietveld refinement method combined with Raman spectra analysis reveal that all compositions are only crystallized into zinc ferrite (ZnFe2O4) after high-temperature treatment at 1000 °C for 5 h La3+ ions preferentially reside in BO6 sub-lattice, which corresponds to the expanding unit cell and octahedral volume of ZnFe2O4. The elongation of cation-anion bonds at the BO6 sub-lattice (∼0.02 Å) and the movement of oxygen toward the AO4 sub-lattice play an important role in weakening super-exchange interaction (SE) between sub-lattices and raising the frustration of magnetic structure as confirmed by the electron density (ED) mapping analysis. The particle size of the sample was decreased from ∼1400 nm for x = 0.01–∼600 nm for x = 0.04. These factors were found to cause the decrease of the magnetization values (Ms and Mr) and the increase of field coercivity due to the increase of La3+ ions substitution. The substitution of La3+ ions are found effective to improve the microwave absorbing (MA) ability of zinc ferrite. The trends of MA ability are related with the different spin-orbit coupling of La–Fe, impedance matching characteristic, natural magnetic resonance, and particle size distribution. The substitution of La3+ ions in the composition of x = 0.04 (ZnLa0.04Fe1, 96O4) affected the full coverage of the EAB across the entire X-band frequency range, making it an excellent microwave absorbing materials (MAMs) candidate.