Synthesis and magnetic properties of barium–calcium hexaferrite particles prepared by sol–gel and microemulsion techniques

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Abstract

The preparation of W-type hexaferrite particles with the composition BaCa2Fe16O27 by microemulsion and a stearic acid sol–gel method with and without surfactant has been investigated at various sintering temperatures. The structural and magnetic characteristics have been studied by X-ray diffraction (XRD), a vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetric (DSC) and Fourier transform infrared (FTIR) techniques. The effect of sintering temperature on the properties of BaCa2Fe16O27 hexaferrites has been studied. The value of saturation magnetization (Ms) depends on types of surfactant used. The sample prepared in the presence of polyoxyethylene (20) sorbitan monooleat (Tween 80) shows low saturation magnetization (Ms=15.10 emu/g), whereas the other sample prepared in the presence of a surfactant cetyltrimethylammonium bromide (CTAB) exhibits high saturation magnetization (Ms=24.60 emu/g) compared to the normal sample.

Introduction

Hexagonal ferrites are very attractive materials for high-frequency circuits and operating devices. They are widely used as permanent magnets, high-density magnetic recording media and microwave devices. Barium hexagonal ferrites are suitable candidates for high-density, over-coat-free, contact or semi-contact recording media [1]. On account of their superior chemical stability, mechanical hardness, excellent corrosion and wear resistance, and low level of media noise, they are suitable for rigid disk media without protective and lubricant layers. Due to large magneto-crystalline anisotropy and strong dependence of the orientation of easy axis on the microstructure, they have potential for application in both perpendicular and longitudinal magnetic recording media [2], [3], [4].

Hexagonal ferrites are divided into six different types: M(AFe12O19), W(AMe2Fe16O27), X(A2Me2Fe28O46), Y(A2Me2Fe12O22), Z(A3Me2Fe24O41), U(A4Me2Fe36O60), where A=Ba, Sr, La and Me=a bivalent transition metal [5]. The crystal structure of W-type hexagonal ferrite is very complex and can be considered as a superposition of R and S blocks along the hexagonal C-axis with a structure of RSSR*S*S*, where R is a three-oxygen-layer block with composition BaFe6O11, S (spinel block) is a two-oxygen-layer block with composition Fe6O8 and ‘*’ means that the respective block is turned 180° around the hexagonal axis. The W-type hexaferrite is a very useful material for home appliances, electronic products, communication equipments and data processing devices due to its unique electrical and magnetic properties. The structural and magnetic properties of W-type hexaferrite depend on many factors like method of preparation, sintering temperature, type and amount of substitution, etc. [6], [7], [8], [9], [10]

Hexagonal ferrites are prepared by using various synthesis routes like chemical coprecipitation [11], [12], low-temperature combustion [13], sol–gel [14], mechanical alloying [15], [16], mechanical activation [17], solid-state reaction [18], microemulsion and reverse microemulsion [19], [20], etc. The method of preparation strongly determines the structural and magnetic properties of hexaferrite.

In the present paper, we report the preparation of desired materials of barium–calcium hexaferrite using a microemulsion and stearic acid sol–gel method [21] in the presence of two different surfactants: cetyltrimethylammonium bromide (CTAB) and polyoxyethylene (20) sorbitan monooleate (Tween 80). The presence of surfactants as well as temperature effects on the morphology and phase purity of hexaferrite have been studied.

Section snippets

Powder preparation

Samples with composition BaCa2Fe16O27 were prepared using a stearic acid sol–gel method. The stoichiometric amounts of AR grade powder of iron nitrate (Fe(NO3)2)·9H2O, barium hydroxide (Ba(OH)2) and calcium nitrate (Ca(NO3)2)·4H2O were mixed in an appropriate amount of a stearic acid solution. The mixture was heated at 80–100 °C for 2 h under stirring and then cooled to room temperature. The gel precursor so formed was decomposed at 500 °C for 1 h and subsequently calcinated at 650, 750, 850, 950

Results and discussion

In order to determine the temperature range over which the chemical and structural changes occur, TGA, DSC, FTIR spectra and XRD measurements were recorded. The details are as follows.

Conclusion

A simple sol–gel method in the presence of different types of surfactants as well as in a microemulsion system is used for the preparation of barium–calcium hexaferrite particles. It has been observed that the type of surfactant plays a crucial role in deciding the morphology of the particles. The magnetic studies carried out using the VSM showed that low coercivity was found in the presence of surfactants.

The observations from the SEM and VSM studies are summarized as follows:

  • (i)

    A barium–calcium

Acknowledgments

One of the authors (R.B.J.) is thankful to the UGC, Delhi, for the financial support in the form of Minor Research Project F. No. 31-28/2005 (SR) and IUCAA, Pune for library and computational facilities.

References (32)

  • A.M. Abo El Ata et al.

    J. Magn. Magn. Mater.

    (2000)
  • X.H. Wang et al.

    J. Magn. Magn. Mater.

    (1998)
  • M. El-Saadawy

    J. Magn. Magn. Mater.

    (2000)
  • S.P. Ruan et al.

    J. Magn. Magn. Mater.

    (2000)
  • T. Ogasawara et al.

    J. Magn. Magn. Mater.

    (2000)
  • S.R. Janasi et al.

    J. Magn. Magn. Mater.

    (2002)
  • J. Huang et al.

    J. Magn. Magn. Mater.

    (2003)
  • W. Zhong et al.

    J. Magn. Magn. Mater.

    (1997)
  • J. Ding et al.

    J. Magn. Magn. Mater.

    (1995)
  • G. Mendoza-Suarez et al.

    J. Magn. Magn. Mater.

    (2001)
  • J. Subrt et al.

    Solid State Ion.

    (1993)
  • D. Makovec et al.

    J. Magn. Magn. Mater.

    (2005)
  • Xiaohni Wang et al.

    J. Alloys Compds.

    (1996)
  • K. Jisheng et al.

    J. Magn. Magn. Mater.

    (1983)
  • J.J. Temuujin et al.

    J. Solid State Chem.

    (2004)
  • M.Y. Salunkhe et al.

    Vibr. Spectrosc.

    (2004)
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