Investigation of structural and magnetic properties of nanocrystalline manganese substituted lithium ferrites

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Abstract

Nanocrystalline manganese substituted lithium ferrites Li0.5Fe2.5−xMnxO4 (2.5≤x≥0) were prepared by sol–gel auto-combustion method. X-ray diffraction patterns revealed that as the concentration of manganese increased, the cubic phase changed to tetragonal. Magnetic properties were measured by hysteresis loop tracer technique. All the compositions indicated ferrimagnetic nature. The surface morphology of all the samples was studied by using scanning and transmission electron microscopy. The substitution of manganese ions in the lattice affected the structural as well as magnetic properties of spinels.

Graphical abstract

The synthesized nanoparticles shapes, sizes and size dispersibilities were obtained from the transmission electron microscopy (TEM). The TEM micrographs of synthesized samples revealed that, spherical shape with average particle size 50 nm. Selected area electron diffraction pattern (SAED) suggests the polycrystallinity and also the formation of spinel ferrites.

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Introduction

Ferrospinels have interesting structural and magnetic properties and are widely used in many important components such as microwave devices, memory cores, magnetic recording media, transformers, choke coils, high frequency instruments, data storage, noise filters and recording heads, owing to their high magnetic permeabilities and low magnetic losses [1], [2]. These properties are dependent on the nature of ions and their charge distribution among tetrahedral and octahedral sites. In spinels, the oxygen ions form a cubic close packed array, in which the A site cations occupy one-eighth of the tetrahedral sites and the B site cations are distributed over one half of the octahedral positions. The modifications of the structural and magnetic properties of ferrites are due to substitution of different ions and have been studied by various workers [3], [4], [5], [6], [7], [8].

Here, we report the substitution of manganese in lithium ferrite and its effect on structural and magnetic properties.

Section snippets

Experimental details

Polycrystalline samples having the general formula, Li0.5Fe2.5−xMnxO4 (0.0≤x≤2.5) were synthesized by sol–gel auto-combustion method. High purity AR grade ferric nitrate, manganese nitrate, lithium nitrate and citric acid were used for synthesis. The metal nitrate solutions were mixed in the required stoichiometric ratios in distilled water. The pH of the solution was maintained between 9 and 9.5 using ammonia solution. The solution mixture was slowly heated around 373 K with constant stirring

X-ray diffraction

X-ray diffraction patterns of the Mn-substituted lithium ferrite samples are shown in Fig. 1. From Table 1, it is noted that, the manganese substituted lithium ferrites are cubic in the range 1.5≤x≥0.0 and tetragonal in the range of 2.5≤x≥2.0. The tetragonal structure for x=2.0 and 2.5 is due to the Jahn–Teller effect of Mn3+ ions [9]. The lattice constant increases with substitution of manganese content upto x=1.5, there after decreases due to the tetragonal distortion. The increase in lattice

Conclusions

Manganese substituted lithium ferrites of nanocrystalline nature were synthesized by sol–gel auto-combustion method. The distribution of cations in Li0.5Fe2.5−xMnxO4 system has been studied using Burger method. The system shows cubic phase for x≤1.5 and tetragonal for x≥2.0. From X-ray intensity calculations, it is noted that Mn3+ ions show strong preference towards octahedral site. The ferrospinels synthesized by auto-combustion method were in nanocrystalline range (∼50 nm). The saturation

Acknowledgment

Author (PPH) is very thankful to UGC, New Delhi for financial assistance through Major research project F.No.32–289/2006 (SR).

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