Role of Mg2+ and In3+ substitution on magnetic, magnetostrictive and dielectric properties of NiFe2O4 ceramics derived from nanopowders

Abstract

The effect of Mg²⁺ and In³⁺ substitution on the structural, magnetic, magnetostrictive and dielectric properties of NiFe₂O₄ samples derived through sintering of nanocrystalline ceramic powders is investigated. Namely, NiFe₂O₄, NiMg_0.2Fe_1.8O₄ and NiIn_0.2Fe_1.8O₄ nanopowders were synthesized by a tartrate-gel route followed by calcination at 500 °C, pelletization and sintering at 1200 °C for 2 h. The average particle size was found to decrease from ∼13 nm (for NiFe₂O₄) to ∼9 nm and ∼7 nm for as-synthesized Mg²⁺ and In³⁺ substituted NiFe₂O₄ samples (after calcination), respectively. However, after sintering a better grain growth occurs for the In³⁺ substituted sample, as confirmed through the microscopy and dielectric results. Due to the replacement of smaller Fe³⁺ cations by larger In³⁺ and Mg²⁺ cations at the tetrahedral (T_d) and octahedral (O_h) interstitial positions, respectively, in the spinel structure of NiFe₂O₄, the lattice parameters increase in both the cases. The T_d site occupation of In³⁺ leads to higher magnetization for the NiIn_0.2Fe_1.8O₄ sample, but O_h site occupation of Mg²⁺ leads to lower magnetization for the NiMg_0.2Fe_1.8O₄ sample, in comparison to the pure NiFe₂O₄ sample. Furthermore, the Curie temperatures (T_C) and magnetocrystalline anisotropy constants (K₁) for both the samples are considerably lower than the parent compound, with all the parameters being the lowest for the In³⁺ substituted sample because the T_d occupation of non-magnetic In³⁺ drastically decreases the A–O–B magnetic superexchange interactions. The above alteration to the magnetic interactions alters the magnitude of maximum magnetostriction (λ_max), which is explained based on the occupation of the Mg²⁺ and In³⁺ cations in our samples. The obtained magnetostriction properties of our samples are very useful for magnetostriction based sensor application.