Structural, magnetic and electric properties of multiferroic NiFe2O4-BaTiO3 composites

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Highlights

  • In this work, the standard and straightforward method of solid-state reaction and direct mixing of ferrite and ferroelectric phases were used to prepare high-quality magnetoelastic multiferroic composites, (x)NiFe2O4 + (1 − x)BaTiO3.

  • The significant change in temperature-dependent magnetization curves of NiFe2O4-BaTiO3 composite multiferroics at structural phase transitions of BaTiO3 is a clear signature of the strain-mediated converse magnetoelectric effect.

  • The NiFe2O4-BaTiO3 composite system will be a potential candidate for future low-power consumption device applications at room temperature.

Abstract

The room-temperature magnetoelastic coupling has been demonstrated in (x)NiFe2O4 + (1 − x)BaTiO3 (where x = 0–1 with a difference of 0.1) composite system by investigating its structural, magnetic and ferroelectric properties. The samples were prepared by the standard solid-state reaction method and characterized by x-ray diffraction, backscattered scanning electron microscopy and energy dispersive x-ray spectroscopy techniques. The temperature dependent magnetization data clearly show significant jumps in magnetization curves at structural phase transitions of BaTiO3, signifying the strain-mediated converse magnetoelectric (CME) coupling in NiFe2O4-BaTiO3 multiferroic system. The substantial changes observed in the obtained parameters from structural, magnetic and ferroelectric properties clearly ensure the strain-mediated magnetoelectric (ME) as well as CME effects in this system. The present investigation indicates that the NiFe2O4-BaTiO3 composite system will be a potential candidate for the future low-power consumption device applications at room temperature.

Introduction

Magnetoelectric (ME) multiferroics composed of ferro(/ferri)magnetic (FM) and ferroelectric (FE) composites have drawn a significant attention of the scientific community in the recent past due to their possible room-temperature (RT) device applications [1], [2], [3]. The ME materials possess FM and FE properties simultaneously, in which the applied magnetic field controls the electric polarization (direct ME effect), or an electric field can induce the magnetization (converse ME effect). However, this intriguing ME effect was realized only in few single-phase materials and the coupling occurs only under extreme conditions, such as low-temperatures and/or high-magnetic fields and observed ME effect at RT is very weak [4]. The reasons are quite clear; the requirements for FM and FE orders in crystalline materials have the opposite requirements [5]. Alternatively, the ME multiferroics composed of FM and FEs possess strong ME coupling thereby multiferroic property originates from the combined effect of individual phases, but these phases separately do not show the multiferroic behavior. One of the challenging aspects of these materials is to realize the robust ME coupling in bulk composite form. Therefore, to achieve high ME coupling in bulk composites, one should completely eradicate the chemical reaction between FM and FE phases during the material processing. In most of the cases, the chemical reaction may likely to form a dead-layer, which weakens ME coupling in the composites. The other requirement could be the combination of high piezoelectric coefficient of FE phase and high magnetostriction coefficient of FM phase materials. Also, to achieve suitable mechanical coupling across the hetero-interface, it should be free from microstructural defects.

In the present study, a FM material, NiFe2O4 (NFO) has been chosen as a magnetic phase in the composite due to its excellent RT magnetic properties. The spinel ferrite, NFO is widely studied magnetic material and known for its low anisotropy, large resistivity and high piezomagnetic properties. Also, due to its soft-ferrimagnetic nature, NFO exhibits high permeability, which is one of the prerequisites for the promising ME coupling in composite samples [6]. The FE material, BaTiO3 (BTO) is one of the most widely explored lead-free, room-temperature FE materials, used in several applications. Also, BTO undergoes three structural phase transitions in FE phase; i.e., tetragonal to orthorhombic to rhombohedral at temperatures, 280 K and 190 K, respectively. Therefore, BTO gives an opportunity to explore the lattice strain-mediated ME coupling, called magnetoelastic coupling in composites [7]. The lattice mismatch between BTO and NFO lattice grains at the interface is minimal to make the intimate interface to legalize a promising magnetoelastic coupling. Interestingly, different mole ratios of NFO and BTO phases in composites enable to study the strain-mediated direct and converse ME effects in this composite system. In the present work, a systematic investigation of magnetoelastic coupling in NFO and BTO bulk composites has been taken up by a thorough comprehensive study of structural, morphological, magnetic and ferroelectric properties.

Section snippets

Experimental details

Polycrystalline single phase NFO and BTO were prepared by the standard solid-state reaction method using (Sigma Aldrich chemicals) NiO (99.99%), Fe2O3 (99.98%), BaCO3 (99.98%) and TiO2 (99.99%) ingredients as starting materials. After mixing the ingredients of NFO and BTO separately in the stoichiometric ratios, the mixed component powders was ground for several hours with subsequent calcinations at different temperatures ranging from 1000 °C to 1250 °C for 8 h each. The powders of individual

Structural characterization

Fig. 1 shows the XRD patterns (for x = 0, 0.2, 0.4, 0.6, 0.8 and 1) of the samples in the present investigation. The data were collected carefully by considering the ratio between the full-width at half-maxima (FWHM) of the diffraction peak and the step-size; this ratio is almost equal to 5, which is an acceptable parameter for a quality data collection by any diffractometer [8]. However, in composites of FE and FM materials, the scope for the third phase is prominent compared to single phase

Conclusion

In summary, the solid-state reaction and direct mixing methods were successfully implemented to obtain the magnetoelastic multiferroic composite with compositional formula, (x)NiFe2O4 + (1 − x)BaTiO3 (where x = 0–1 with a difference of 0.1). The structural, morphological, compositional, magnetic and ferroelectric characterizations were thoroughly studied on the prepared samples. The x-ray diffraction data confirms the coexistence of spinel, NiFe2O4 and perovskite, BaTiO3 phases without any

Acknowledgements

The authors are grateful to the Department of Science and Technology (SERB grant no.: SB/FTP/PS-057/2014), University Grant Commission (BSR start-up-grant no.: F.30-107/2015), Council of Scientific and Industrial Research (grant no.: 03(1344)/16/EMR-II), India for financial support. The authors also thank Dr. A. R. James, Defence Metallurgical Research Laboratory, Hyderabad for extending ferroelectric property measurements facility. One of the authors (PB) would like to thank UGC for awarding

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