Tuning of structural, magnetic and dielectric properties of TFe2O4 (T = Mn, Fe, Co, Ni, Cu, and Zn) Nano-Hollow Spheres: Effect of cation substitution

Abstract

Nano hollow sphere (NHS) is an emerging morphology among magnetic nanostructures and here, NHSs of spinel ferrites (TFe2O4, T = Mn, Fe, Co, Ni, Cu, and Zn) are synthesized in a facile solvothermal method and their structural, magnetic and dielectric properties are investigated in detail. These properties are found to largely depend on different divalent cation placements in the ferrite structures. Coercivity of TFe2O4 samples are observed to vary from ∼576 Oe (T = Co) to ∼ 116 Oe (T = Ni) and saturation magnetization, from ∼73.6 emu/g (T = Fe) to ∼ 53.6 emu/g (T = Mn), discussed in terms of anisotropy, super-exchange interaction and crystallite size of the materials. Variation of dielectric properties such as permittivity, dielectric loss and ac conductivity of these NHSs within frequency range 10 Hz −5.5 MHz at ∼300 K are explained on the basis of Maxwell-Wagner two layer model for space charge and polaron hopping from Fe3+ to Fe2+ as well as T2+ to T3+ ions at tetrahedral (A) and octahedral (B) sites. Analysis of dielectric relaxation mechanism ensures it as modified-Debye type and Jonscher’s power law displays ac conduction mechanism for TFe2O4 NHSs. Cole-Cole plots are fitted with equivalent circuit to understand the effect of resistive grain boundary and conductive grains with frequency. This study on tunable dielectric and magnetic properties with substitution of different cations provides a map to select an efficient material for applications from high-frequency devices to bio-medical field.