Rakesh Kumar Singh , A. Narayan , A. Yadav , S.Layek , H. C. Verma

Rakesh Kumar Singh , A. Narayan , A. Yadav , S.Layek , H. C. Verma

Department of Physics, Patna Women's College, Patna University, Patna, Bihar, India

Department of Physics, Patna University, Patna, Bihar, India

Vidyavihar Institute of Technology, Purnea, Bihar, India

Department of Physics, IIT Kanpur, Kanpur, India

Abstract


Nanocrystalline Nickel Zinc Ferrite particles (NixZn1- xFe2O4) with different composition were prepared by Citrate precursor method. The ferrite powders were characterized using X-ray diffraction (XRD), Vibrating sample magnetometer (VSM) and Mossbauer Spectroscopy tools. The maximum value of saturation magnetization was observed as 52.18 emu/g and Coercivity as 116.10 Oe in sample with x = 0.8. The Mossbauer spectroscopy results show two environments for iron nuclei. In contrast to bulk Ni-Zn ferrites, the lattice parameter in our samples has a tendency to nonlinearly decrease with increase in the proportion of Nickel. The range of average particle size is 7 nm to 18 nm as obtained from XRD line broadening.

Keywords: Ferrite, Nanoparticle, Magnetic Properties, Mossbauer studies

Introduction

Nanocrystalline Spinel Nickel zinc ferrites have been investigated extensively in recent years because of their potential applications in various electronics devices, radio frequency circuits, high quality filters, rod antennas, transformers, read-write heads for high speed digital tape recorders and magnetic storage devices1,2,3. Their multifarious use in electronics industry stems from the fact that they have large permeability even at high frequency4. Moreover, they have remarkably high electrical resistivity, mechanical hardness, chemical stability and reasonable cost. Several researchers have used citrate precursor method for synthesis of ferrites in bulk as well as nano sizes due to its attractive features like low cost and ease of preparation5-11. We have also used the same method for preparing our samples.

Materials and methods

Synthesis of Ni-Zn Ferrite Nanoparticles: Samples of nanometer-sized nickel-zinc ferrite powder, NixZn1- xFe2O4(x=0.2, 0.4, 0.5, 0.6, 0.8) were prepared by using the Citrate precursor method. Ferric nitratenickel nitrate and Zinc nitrate were taken in stoichiometric proportions as starting materials. Aqueous solutions of these salts were prepared separately by dissolving the salt in minimum amount of deionized water while stirring constantly. The solutions were then mixed together. Aqueous solution of citric acid was prepared in adequate quantity by weight and was added to the prepared salt solutions. The mixture was heated at temperature about 60oC to 80oC for two hours with continuous stirring. This solution was allowed to cool to room temperature and finally it was dried at 90-95oC in an oven until it formed a brown color fluffy mass. This precursor was heated at 450oC for one hour in a muffle furnace. By this process, the precursor decomposed to give nickelzinc ferrite powder consisting of nanometer size particles.

Results and Discussions

Structural features: The ferrite samples prepared as described above were structurally characterized using large angle X-Ray Diffractometer (XRD). In all our samples of Ni-Zn mixed ferrites, XRD patterns show diffraction peaks that correspond to spinel ferrites mainly, together with small peaks of Hematite (Figure 1) and sodium Zincate tetrahydrate. However, the intensities corresponding to these impurity phases are small. Similar peaks were also observed in Ni-Zn ferrite samples prepared using hydrothermal technique4. Albuquerque et al. (2000) have prepared ferrite samples by coprecipitation technique with heat treatment at 300oC as well as higher temperatures12 and it was shown that samples exhibit good structural ordering only for heat treatment at temperature higher than 400oC. The other phases (in addition to spinel) may be attributed to inaccuracy in stoichiometric proportions, inhomogeneity at microscopic scale and presence of unreacted chemicals in the finished product. The lattice constant was observed to change with the proportion of nickel. Apart from the anomalous result for x= 0.2, as the proportion of nickel is increased from x= 0 to 0.8, the lattice constant shows a decreasing trend. A similar trend has also been reported for bulk nickel-zinc ferrite materials earlier

Fig.1: XRD pattern for Ni0.8Zn0.2Fe2O4 Nanomaterials


Fig. 2: Variation of Lattice constant with percentage increase of Nickel
Magnetic and Mossbauer studies: The ferrite samples were magnetically characterized using VSM as well as by Mossbauer spectroscopy. The magnetic parameters obtained from VSM measurements of the six samples of Ni-Zn mixed ferrite particles are tabulated in Table 1. The magnetic hysteresis curves for Ni0.8Zn0.2Fe2O4 nanoparticles are shown in figure


Fig. 3: Hysteresis Loop for Ni 0.8Zn 0.2Fe2O4 Nanoparticles

The values of the magnetization parameters do not show a systematic trend with change in composition. Partly the impurity phases and partly the varying particle size might be responsible for this. The annealing temperature of 4500 C may not be optimum for all the samples. The most interesting case seems to be with Ni0.8Zn0.2Fe2O4 ,where both the coercive field (116.10 Oe) and the saturation magnetization (52.18 emu/g) are largest. Values of saturation magnetization higher than 50 emu/g have so far been achieved by using other methods14,15, only through sintering at temperatures much above 450oC, the sintering temperature used in the present method. Synthesing ferrite samples at lower temperatures have its own advantages as the grain growth is checked and one is more likely to get strain-free nanoparticles.

Caizer and Stefaneseu15 have reported that the magnetic properties are determined by the size of the nanocrystallites. The decrease in saturation magnetisation with decrease in particle size of the nanocrystallites can be attributed to surface effect, spin canting and broken exchange bonds16. In our studies, we have also obtained lowering of saturation magnetization as compared to bulk values.
Fig. 4: Mossbauer Spectrum for Ni 0.8Zn 0.2Fe2O4 Nanomaterials

The Mossbauer pattern of the Ni0.8Zn0.2Fe2O4 sample (Fig. 4) shows that two sextets are superposed, one over the other. Ni-ferrite is an inverse ferrite and one expects Fe ions to occupy both A and B sites. Zn has a preference for A-sites and hence the area corresponding to the A-site sextet should be somewhat smaller to that corresponding to B-site. The well resolved six-line pattern shows that there are no significant superparamagnetic fluctuations of the magnetic moment. However, the Bhf values of the sextets in the spectrum (47.6 T and 43.5 T) are less than the values expected for bulk samples (50 T to 55 T) indicating the fact that the particles are in nanosize but the blocking temperature is above room temperature. The XRD peak broadening for this particular sample gives the average particle size to be 18 nm consistent with the reduced Bhf.

Conclusion We used a single annealing temperature for all our samples of nanocrystalline Ni-Zn mixed ferrite. We observed that the magnetic properties as well as particle size depended on stoichiometric proportion of Nickel and Zinc. The maximum saturation magnetization was found to 52.18 emu/g. This might be a feature of the citrate precursor method that was used by us. The lattice parameter has a tendency to decrease with increase in the proportion of Nickel but we did not get a straight line function as has been reported for the case of bulk ferrites. The Mossbauer spectrum shows that Fe occupies both the A and B sites in the sample and superparamegnetic fluctuations are not significant.

Acknowledgement

Authors, Rakesh K. Singh and A. Yadav are thankful to Nalanda Open University, Patna for partial financial support for this work.

Reference

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Corresponding Author: Email: rakeshpu@yahoo.co.in

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