Determination of ferrimagnetic and superparamagnetic components of magnetization and the effect of particle size on structural, magnetic and hyperfine properties of Mg0.5Zn0.5Fe2O4 nanoparticles

Abstract

The fine-tuning of magnetic parameters and the identification of different magnetic phases are essential for the effective utilization of magnetic nanoparticles. In this work, we aim at controlling the magnetic parameters of Mg0.5Zn0.5Fe2O4 nanoparticles by varying the particle size and to determine magnetic phases using three analytical techniques having different operating time scales: VSM, ESR, and Mössbauer spectroscopy. Single-phase cubic spinel structured Mg0.5Zn0.5Fe2O4 nanoparticles were prepared by the sol-gel auto-combustion route and calcinated at 200, 300, 500, 700, and 900 °C. The cation distribution and structural parameters obtained from the Rietveld analysis had an insignificant variation with the calcination temperature. From the TEM analysis, an increase of the average particle size from 5 to 38 nm and widening of the particle size distribution with the calcination temperature were found. The saturation magnetization increased from 25.6 to 43.7 emu/g with the particle size due to the reduction in the magnetic dead layer thickness. The coercivity decreased from 128 to 31 Oe and the blocking temperature from 76 to 38 K with the particle size and these variations are explained in terms of surface anisotropy and dipolar interactions. Ferrimagnetic, superparamagnetic, and paramagnetic components of magnetization were deconvoluted by the curve fitting of room temperature VSM data. The ferrimagnetic component increased from 56% to 74% and the superparamagnetic component decreased from 37% to 20% respectively with the particle size. The ESR and Mössbauer spectroscopy also identified the ferrimagnetic and superparamagnetic components in the samples and their variations with the particle size were found to be in agreement with that of VSM. Thus, the variation of magnetic parameters in correlation with the particle size offers the possibility of fine-tuning the magnetic parameters of nanoparticles by adjusting the particle size. The deconvolution of magnetic phases using the three analytic methods revealed the coexistence of ferrimagnetic and superparamagnetic components of magnetization in Mg0.5Zn0.5Fe2O4 nanoparticles. Also, this deconvolution unveiled the particle size dependence on the emergence of inhomogeneity in magnetic phases of the samples.