Impact of Mg2+ and Zn2+ substitution on the structure, magnetic anisotropy and magnetostriction of NiFe2 O4

Abstract

The atomistic origin of microstructure, magnetic-anisotropy and magnetostriction behavior in Zn²⁺ and Mg²⁺ substituted NiFe₂O₄ samples is explored in this work. We have synthesized two series of samples:Ni_1-x Zn _x Fe ₂ O ₄ (NZFO) and Ni_1-x Mg_x Fe₂ O₄ (NMFO), with x = 0.00, 0.25, 0.50, 0.75 and 1.00, by glycinenitrate auto-combustion method. Through a rigorous and self consistent analysis of the X-ray diffraction, scanning electron microscopy, Raman spectroscopy and magnetic measurement results, we demonstrated that the microstructure of the samples is controlled by the size of the ions and the interstitial voids where the ions are substituted in spinel ferrites. Size of the substituting ions below the size of the voids leads to compressive strain in the sample along with decrease in lattice parameter, whereas any size of the ions above the size of the voids leads to tensile strain and increase in lattice parameter than the parent ferrite. As observed, the particle size, agglomeration behavior and overall microstructure are decided by the above aspects. Furthermore, the crystal field effects and related magnetic anisotropy behavior also depend on this strain in the material which is created by the size difference of the substituting ions. This behavior leads to interesting changes in magnitude and sensitivity of magnetostriction. We have observed that Zn²⁺ substitution that occupied at the tetrahedral interstitial voids in NiFe₂O₄ leads to crystallographically, mechanically and chemically stable compounds as we approach towards pure ZnFe2O4 , owing to the fact that the size of Zn2+ is similar to the tetrahedral void, perfectly fitting at that position. Whereas Mg²⁺ substitution makes the NiFe₂O₄ even more unstable due to smaller size of the Mg²⁺ ions than the octahedral voids in NiFe₂O₄. The derived magnetic anisotropy and magnetostriction behavior are aligned with the interpretation furnished. Our work explores the origin of differences observed in magnetostriction behavior of Zn²⁺ and Mg²⁺ substituted NiFe₂O₄ , which are essential for comprehending the materials' nature for magnetostrictive strain sensor and actuator applications.