Investigation on the effect of ferrite content on the multiferroic properties of (1-x) Ba0.95Sr0.05TiO3 – (x) Ni0.7Zn0.2Co0.1Fe2O4 ceramic composite
Introduction
Recently, the growing demand of electronic device miniaturization and multi-functionality with high performance and low cost has intensified a significant research in the field of multiferroics. Multiferroic materials that combine ferroelectricity and ferromagnetism have stimulated a great deal of interest worldwide due to their promising applications as transducers, magnetic field probes, spintronics devices and actuators etc [1], [2], [3], [4]. These materials demonstrate magnetoelectric (ME) coupling in which electric polarization can be produced by the application of magnetic field or magnetization can be produced by the application of the electric field [5]. Multiferroic materials can be single phase or two phases. Single phased materials demonstrate low Curie or Neel temperature and extremely weak magnetoelectric coupling response, which limits their practical applications in ME devices [1].
Alternatively, multiferroic composites are very promising, which are based on the product property [6] and are investigated widely. They can be easily synthesized by mixing the ferroelectric and ferromagnetic materials in the desired ratios and then sintering. Many research group have explored the various characteristics features of the ME composites. BaTiO3–NiFe2O4, BaPbTiO3–CuFe2O4, BaTiO3-(Ni, Zn)Fe2O4, Pb(Zr, Ti)O3-(Ni, Zn)Fe2O4, Pb(Zr, Ti)O3–CoFe2O4, and (Ba, Sr)TiO3-(Ni, Zn)Fe2O4, etc. are some of the composites that have been studied [7], [8], [9], [10], [11]. There are certain key factors that significantly affect the ME response as discussed by Boomgaard et al. [12] and are as follows. The resistivity of the ferroelectric and magnetic phase should be high, otherwise it results in the leakage of the accumulated charges, and hence, adversely affect the ME output. In addition, the piezoelectric coefficient and magnetostriction coefficient of the ferroelectric and ferrite phases, respectively, must be large.
In the present work, we report the systematic studies on the multiferroic properties of the (1-x) Ba0.95Sr0.05TiO3 – (x) Ni0.7Zn0.2Co0.1Fe2O4 particulate composite system. Barium strontium titanate (BST) is a promising ferroelectric material having pervoskite structure that has been extensively studied. It finds application in microwave devices [13] on account of its high dielectric constant, low dielectric loss and adjustable Curie temperature (Tc) which depends upon the Ba/Sr composition [14]. Ni0.7Zn0.2Co0.1Fe2O4 (NZCF) is selected as a magnetic phase having cubic spinel structure. NiFe2O4 substituted with Zinc (Zn) is known to possess large saturation magnetization, resistivity and magnetostrictive coefficient, combined with mechanical hardness and chemical stability [15], [16], [17]. Also, the substitution of Cobalt (Co) for Ni in NiFe2O4 exhibits large resistivity and magnetostriction coefficient [18], [19]. The resistivity of the NZCF is found to be ∼109 Ω cm which is higher than the value reported for Ni–Zn ferrite [20]. Furthermore, V.L. Mathe et al. studied the magnetostrictive properties of Co–Ni ferrites, and showed that as Co content increases in Ni–Co ferrite, maximum value of magnetostriction increases [21]. Also, J.S. Ghodake et al. investigated the substitution of Co in Ni–Zn ferrite and have reported an increase in magnetostriction constant with increasing cobalt addition [22]. Keeping this in mind, NiFe2O4 substituted with Co and Zn is employed as the magnetic phase and its effect on the multiferroic properties of BST – NZCF composites have been discussed at length. The phase formation and morphology of the composites are examined. The ferromagnetic behavior of the composites is improved while ferroelectric property gets weaken with increasing ferrite content in the composites. The dependence of dielectric properties on the temperature and frequency is also studied. The magnetoelectric coefficient (αE) of the composites is measured as a function of dc magnetic field from 0 to 4 kOe.
Section snippets
Synthesis and characterization
(1-x) Ba0.95Sr0.05TiO3 – (x) Ni0.7Zn0.2Co0.1Fe2O4 magnetoelectric composites with x = 10, 20, 30 and 40 wt% were synthesized by solid state reaction technique. The composites were abbreviated as BST90-NZCF10, BST80-NZCF20, BST70-NZCF30 and BST60-NZCF40 corresponding to 10, 20, 30 and 40 wt% of NZCF, respectively. For the synthesis of Ba0.95Sr0.05TiO3, analytical grade BaCO3, TiO2 and SrCO3 were taken in stoichiometric ratio and milled in distilled water with zirconia media. Similarly, for
XRD analysis
The Fig. 1 shows the X-ray diffraction (XRD) patterns of the constituent phases Ba0.95Sr0.05TiO3 (BST), Ni0.7Zn0.2Co0.1Fe2O4 (NZCF) and the composites. The XRD patterns of the constituent phases are indexed using the standard JCPDS data on BST (JCPDS file no. 05-0626) and NZCF (JCPDS file no. 74-2081) and reveal tetragonal structure for the BST and cubic spinel structure for the NZCF. Furthermore, all the observed diffraction peaks in the XRD pattern of the composites either correspond to BST
Conclusions
In summary, the bi-phase magnetoelectric composites (1-x) Ba0.95Sr0.05TiO3 – (x) Ni0.7Zn0.2Co0.1Fe2O4 are synthesized by solid state reaction technique and the phase formation is confirmed by XRD. SEM analysis combined with EDS results reveals that the NZCF grains are well dispersed in the BST phase matrix. A significant effect of NZCF content on the dielectric behavior of composites has been noticed. All the composites exhibit dispersion in the lower frequency region. In addition, with
Acknowledgement
One of the authors (Richa Sharma) is thankful to the University Grants Commission (UGC), New Delhi, India for providing the research fellowship. The author would like to thank Dr. N. C. Mehra, University of Delhi, New Delhi, India for SEM measurements.
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