Crystal Structure and Magnetic Properties of Mn-Doped Zn-Ferrite Nanoparticles

The Mn_xZn_1−xFe₂O₄ nanoparticles with \(x = 0, 0.25\) , and 0.5 were synthesized by a chemical coprecipitation method. The X-ray diffraction (XRD) patterns were well fitted with single-phase spinel ferrite structure using Rietveld analysis as Fd-3 m space group. The average crystallite size of the nanoparticles estimated from XRD data analysis varies between 4 and 7 nm. The Mössbauer spectra of the nanoparticles at room temperature were fitted with a well-defined single quadrupole splitting for doublet pattern. The magnetization versus magnetic field data at 5 K show hysteresis loops indicating ferromagnetic (FM) cluster behavior. The superparamagnetic nature of the samples is evident. The temperature-dependent magnetization plots in zero field cooled and field cooled mode show increase in blocking temperature from 31 to 115 K with increase in Mn content from 0 to 0.5. The FM resonance (FMR) spectra indicate slight decrease in FM interactions as x increases from 0 to 0.25 followed by a significant increase with further increase in x value to 0.5. The decrease in resonance field ( \(H_{r}\) ) and increase in peak-to-peak linewidth \(\Delta H_{\rm {PP}}\) of the FMR line with decreasing temperature indicates weak antiferromagnetic coupling between the octahedral and tetrahedral sublattices of the spinel ferrite. The replacement of Zn by 50% Mn in Zn-ferrite results in an increase in FM interactions with no significant change in the crystallite size.

I. Introduction

Magnetic nanoparticles are useful in biological, medical, and industrial applications because of their high proportion of surface to volume ratio compared with bulk samples [1]. Nanosized soft ferrites can give high resistivity and saturation magnetization with low magnetic losses, making them suitable in technological applications, such as computer memory, ferrofluids, and pulse transformers operating at high frequency. Size of ferrite nanoparticle is related to its structural and magnetic properties [2]–[6]. The nonmagnetic ions in spinel ferrites can alter its structural, electrical, and magnetic properties. The studies reveal the nature of exchange interaction, direction of magnetization, cation distribution, spin canting and so on. This isomorphism is apparent in their Mössbauer spectra and this drastically reduces magnetic interactions that are related to lower magnetic ordering temperature [7], [8]. General notation of the structure of spinel ferrites can be written as (MeFe [MeFe] O₄, where Me is divalent metal ion. The parenthesis and square brackets refer tetrahedral (A) and octahedral (B) sublattices. The value of trivalent cations Fe³⁺ occupied tetrahedral sites is the degree of inversion (). The magnetic properties originate from the weak antiferromagnetic (AFM) coupling between the A and B sublattices in spinel ferrites.