Steering of Magnetic Interactions in Ni0.5Zn0.5Fe2–x(Mn)xO4 Nanoferrites via Substitution-Induced Cationic Redistribution

Abstract

Ni0.5Zn0.5Fe2O4 is one of the most versatile and technologically indispensable soft magnetic materials; however, a detailed investigation on the effect of substitution-induced cation redistributionon the magnetic and ferromagnetic resonance (FMR) properties of Ni–Zn-nanoferrites (NFs) remains elusive. Herein, we demonstrate that the modulation of the superexchange interactions via dopant-driven cationic redistribution is an efficient way to maneuver the static and dynamic magnetic properties of Mn-substituted Ni0.5Zn0.5Fe2–x(Mn)xO4 NFs. Employing a combination of Raman and X-ray photoelectron spectroscopies, the effect of Mn-doping on cation distribution is revealed. It was found that Mn2+ cations initially occupy tetrahedral A-sites; however, as substitution of Mn increases from Mn = 0.1 to 0.5, the higher percentage of Mn-cation exhibits the Mn3+ oxidation state and preferably occupies the octahedral B-sites. The Mössbauer study elucidates that the Fe3+–O–Mn2+ superexchanges are weaker than the Fe3+–O–Fe3+ superexchange. We demonstrate that the Mn-substitution-driven redistribution of cations is responsible for the remarkable decrease in magnetocrystalline anisotropy. Composition-dependent FMR studies reveal that the substitution of the Fe3+ cation by the Mn2+ cation weakens the magnetic coupling, causing shifts in the FMR relaxation frequency. The analysis of magnetic relaxation suggests that there are two kinds of interparticle interactions present in these NFs, namely, dipolar interaction and the surface spin interaction (broken superexchange). The superparamagnetic NFs with Mn = 0.1 substitution exhibit a magnetization value as high as 58 emu/g along with a very low coercivity of ∼20 Oe, making them an excellent candidate for a broad range of technological applications.