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DOI: 10.1039/C5RA16742F (Paper) RSC Adv., 2015, 5, 105609-105617

Enhanced magneto-capacitance response in BaTiO3–ferrite composite systems

Sreenivasulu Pachari, Swadesh K. Pratihar and Bibhuti B. Nayak*
Department of Ceramic Engineering, National Institute of Technology, Rourkela-769008, Odisha, India. E-mail: bbnayak@nitrkl.ac.in; bibhutib@gmail.com

Received 19th August 2015 , Accepted 7th December 2015

First published on 8th December 2015

Abstract

This research work focuses on the enhanced magneto-capacitance response in the composites of (1 − X)BaTiO3[thin space (1/6-em)]:[thin space (1/6-em)]X(CoFe2O4/ZnFe2O4/Co0.5Zn0.5Fe2O4) (where X = 20, 30 and 40 wt%), prepared via a conventional solid-state mixing route using auto-combustion derived powders. A new observation is the existence of two different types of morphologies such as plate-like (size was ∼5 μm with a thickness ∼1 μm) and fine agglomerated nearly spherical shape of tetragonal BaTiO3 along with the polyhedral morphology (size of ∼0.5 to ∼2.5 μm) of cubic ferrites in the prepared composite systems. Unidirectional or random orientation of the plate-like morphology of BaTiO3 in these composite systems depends on the percentage of ferrite phase. In addition to the morphology effect, the magnetoresistance effect was analyzed using magneto-impedance study as a function of frequency as well as by Cole–Cole plots. The magnetoresistance effect was found to be dependent on the type and percentage of ferrites. The combined effects of phase morphology along with magnetoresistance and/or magnetostriction led to enhanced magneto-capacitance response in these composites. The percentage of magnetocapacitance values were found to be in the range between −3 to −9, −0.5 to −7 and +1.5 to −1.5 for BaTiO3[thin space (1/6-em)]:[thin space (1/6-em)]CoFe2O4, BaTiO3[thin space (1/6-em)]:[thin space (1/6-em)]ZnFe2O4 and BaTiO3[thin space (1/6-em)]:[thin space (1/6-em)]Co0.5Zn0.5Fe2O4 composites, respectively, depending on the percentage of ferrite phase.

Introduction

Magneto-dielectric composite materials are those which possess both magnetic and dielectric properties. Due to the stress mediated mechanical coupling between the dielectric [such as barium titanate (BaTiO3)] and ferromagnetic (such as ferrites) phases, the magnetic properties can be controlled by an applied electric field, while the dielectric properties can be controlled by applying a magnetic field.1–9 One of the important properties of magneto-dielectric composite system is magneto-capacitance response, which has potential applications in the field of sensors, actuators, and devices.1,2,4,10–14 The magneto-capacitance response strongly depends on the magnetoresistance of grain or grain boundary, magnetostriction of ferrite phase as well as concentration of ferrite phase.4,8,14 Also the distribution of ferroelectric (BaTiO3) and ferrimagnetic ferrites phases with different morphologies was reported to modify both magnetic and dielectric properties and hence magneto-capacitance of the composite system.15 Different morphologies of BaTiO3 including spherical, cuboid, feather, pillars-like and polyhedral type ferrites have been explored in the BaTiO3[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite system via various wet chemical synthesis methods such as molten-salt method, sol–gel method and hydrothermal-polymer assisted in situ methods, respectively.1,2,10,16–23 Raidongia et al.,15 reported that magnetocapacitance increased from 1.7% to 4.5% by changing the morphology from core–shell nano particles to core–shell nanotubes. Change in the magnetocapacitance was also observed by Mandal et al.,14 in which Co0.65Zn0.35Fe2O4–PbZr0.52Ti0.48O3 magnetoelectric composites were prepared by sol–gel technique and had maximum magneto-capacitance change of 1.15% for 30 weight percent ferrite composite. Among different synthesis routes, solid-state mixing route was well established and lots of research has been carried out to prepare magneto-dielectric composites systems.1,11,12,19–24 But, the formation of different morphologies of BaTiO3 or ferrite via solid-state mixing route is a challenge. So, combination of wet-chemical synthesis followed by solid-state mixing may be an another way to explore different types of morphologies of BaTiO3 or ferrite in magneto-dielectric composite systems. Among the wet-chemical routes, auto-combustion has advantage of consuming less energy and time for developing oxide material.24 Very few literatures are available for developing magneto-dielectric composite systems by solid-state mixing of auto-combustion derived powders. In this present work, three different types of ferrite were incorporated in the matrix of BaTiO3 for the development of BaTiO3[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite materials via conventional solid-state mixing route using auto-combustion derived powders. Incorporation of different resistive ferrites, may expect to modify the magnetocapacitance response of the magneto-dielectric composite materials. Thus, an attempt has been made to study the magneto-dielectric properties especially magneto-capacitance behavior of the composite with three different types of ferrites such as CoFe2O4, ZnFe2O4 and Co0.5Zn0.5Fe2O4. The ferrite composition has been chosen based on the basis of their different electrical resistances.25 Moreover, different morphology of BaTiO3 along with different types of ferrite may enhance the magneto-capacitance response of these composite systems. So, the main objectives of this present work are (i) to explore different types of morphologies of barium titanate or ferrite in BaTiO3[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems prepared via solid-state mixing of auto-combustion derived individual powders and (ii) to study the effect of ferrite type (CoFe2O4, ZnFe2O4 and Co0.5Zn0.5Fe2O4) as well as its concentration on the microstructure and magneto-dielectric properties of BaTiO3[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems.

Experimental

Raw materials such as barium nitrate [Ba(NO3)2], titanyl nitrate [TiO(NO3)2], citric acid [C6H8O7], ammonium nitrate [NH4NO3] and EDTA [C10H16N2O8] were taken in the molar ratio of 1[thin space (1/6-em)]:[thin space (1/6-em)]1[thin space (1/6-em)]:[thin space (1/6-em)]1.5[thin space (1/6-em)]:[thin space (1/6-em)]12[thin space (1/6-em)]:[thin space (1/6-em)]0.1, respectively, for the synthesis of BaTiO3 via auto-combustion route. Similarly, ferric nitrate non-ahydrate [Fe(NO3)3·9H2O], cobalt nitrate hexa hydrate [Co(NO3)2·6H2O], zinc nitrate hexa-hydrate [Zn(NO3)2·6H2O] and citric acid [C6H8O7] (3 moles citric acid was used for the mole of ferrite synthesized) were selected as raw materials in appropriate molar ratio for the combustion synthesis of ferrite compounds such as CoFe2O4, Co0.5Zn0.5Fe2O4 and ZnFe2O4 via auto combustion method. The individual precursor solution for synthesizing BaTiO3 or ferrites was preceded by dissolving appropriate amount of the required reagents in distilled water and followed by adding ammonia to the precursor solution in order to achieve pH ∼ 7. This solution was kept at 80 °C under continuous stirring till a viscous gel was formed and this viscous gel proceeded by self-ignition followed by combustion. After combustion, the residue was collected and grounded in agate-mortar to form as-synthesized individual powders of BaTiO3 and ferrites. The combustion derived as-synthesized BaTiO3 and ferrites powders were calcined at 1000 °C for 6 h and 900 °C for 4 h, respectively.

Further, the auto-combustion derived calcined ferrite (CoFe2O4/ZnFe2O4/Co0.5Zn0.5Fe2O4) powders of 20, 30 and 40 wt% and appropriate amount of BaTiO3 were mixed properly in agate mortar using 3 wt% PVA solution as binder. The dried mixed powders were compacted to pellets (average diameter and thickness of pellets are 10.70 mm and 1.3 mm) and sintered at 1250 °C for 4 h based on the literature data.26–28 Phase analysis using X-ray diffractometer [model: Rigaku Ultima-IV, Japan], microstructure using Field Emission Scanning Electron Microscopy (FESEM) [model: NOVA Nano SEM/FEI 450], M–H loop measurement using M–H loop tracer [make: Magenta, India], dielectric measurements using LCR meter [model: HIOKI 3532-50 LCR Hitester] [Signal amplitude 100 mV, zero d.c. bias was used and data was produced using RC parallel circuit model], P–E loop measurement using P–E loop tracer [make: Marine India, Electronics] and magneto-capacitance [percentage MC = {(ε(H) − ε(H = 0))/ε(H = 0)} × 100, where ε(H) is permittivity at field and ε(H = 0) is permittivity without field] measurement (at 1 KHz) using both electromagnet [make: GMW magnet system, USA] and LCR meter were performed. In this paper, samples are specified with notation such as XBT$Y ferrite, where X stands for wt% of BaTiO3 (BT) phase, $ stands for solid-state mixing and Y stands for wt% of ferrite phase (CF/ZF/CZF).

Results and discussion

Phase analysis of the sintered pellets of BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems were analyzed using X-ray diffraction pattern (XRD) and are shown in Fig. 1.
image file: c5ra16742f-f1.tif
Fig. 1 X-ray diffraction patterns of BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems.

All the peaks were identified with either tetragonal BT (marked as *) or cubic ferrite (marked as ♦) in the XRD pattern, as per the JCPDS data file (for BT: JCPDS file no: 75-2116 and for ferrite: JCPDS file no: 22-1086, 73-1963). In addition to these primary phases, minute amount of barium hexa-ferrite11,29 (BaFe12O19) was also observed in all composites, due to diffusion of Fe2+ or Fe3+ ions in to Ti3+ site.30 It was also observed that the peak intensity of ferrite phase increases with increase in ferrite percentage in all composite systems.31 The crystallite size of BT phase was found to be comparatively larger in size than the crystallite size of ferrite in the BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems. The crystallite size of BT phase was in the range between 26 nm and 34 nm, whereas, the crystallite size of ferrite was found to be in between 18 nm and 32 nm.

In order to study the microstructure, Field Emission Electron Microscopy (FESEM) was performed on BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composites. Fig. 2 shows FESEM micrographs of BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrites (CF/ZF/CZF) composite systems.


image file: c5ra16742f-f2.tif
Fig. 2 FESEM micrographs of BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems. BT and ferrite phases were identified by arrow mark.

Three different types of morphologies such as plate, polyhedral and agglomerated with nearly spherical-like phases were present in these composite systems. To further confirm the phases in the microstructure of BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite system, elemental mapping of typical 7BT$3ZF composite was performed and shown in Fig. 3. From elemental analysis, it was clear that the plate and agglomerated nearly spherical-like morphologies belong to BT phase and the polyhedral-like morphology was ferrite phase. From FESEM micrographs in Fig. 2, it was confirmed that the particular plate-like BT phase was prominent in 7BT[thin space (1/6-em)]:[thin space (1/6-em)]3 CF/ZF/CZF composite systems. In these particular composites, the plate-like BT phase was randomly oriented and the plates in vertical position resembling rod-like morphology. However, the plate-like BT phase was also present but orientated in one direction for other compositions. From primary investigation of FESEM images, it would be presumable that the growth of polyhedral ferrite in 20 wt% ferrite based composites is lower and not sufficient enough to orient the plate-like morphology of BT phase and thus plate-like BT phase orient in one direction in 8BT[thin space (1/6-em)]:[thin space (1/6-em)] 2 CF/ZF/CZF composite systems. As the percentage of ferrite increases to 30 wt%, the polyhedral ferrite phase is prominent and its growth is sufficient to orient the plate-like BT phase in random way. Further increase of ferrite to 40 wt%, the growth of polyhedral ferrite phase increases and also partially covers the plate-like BT phase. So, in 6BT[thin space (1/6-em)]:[thin space (1/6-em)] 4 CF/ZF/CZF composite systems unidirectional plate like BT and polyhedral ferrite phases are with nearly same size and distribute undistinguished. The size of BT plates was ∼5 μm with a thickness ∼1 μm, whereas polyhedral ferrite was in between 0.5–2.5 μm. Both BT and ferrite phases were well packed and seem to be highly dense. The density of these composites increases with ferrite content and varies in between 89–91%.


image file: c5ra16742f-f3.tif
Fig. 3 Elemental mapping of 7BT$3ZF composite [green: BT, blue: Ti, red: Zn and pink: Fe].

The variation of microstructure of BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems may lead to modify the dielectric and magnetic properties of these composites. So, one of the dielectric properties such as permittivity as a function of frequency of composite systems was analyzed at room temperature and are shown in Fig. 4.


image file: c5ra16742f-f4.tif
Fig. 4 Permittivity as a function of frequency for BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems.

Generally, for this type of composites, the permittivity decreases with frequency.29 In this composite systems, it was observed that the permittivity was nearly independent with frequency for the composites having 20 wt% ferrite. However, the permittivity was dependent on frequency for the composites having 30 and 40 wt% ferrite. The nature of nearly independent or dependent permittivity with frequency for BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composites may be depended on the concentration of BT phase and morphology along with distribution of BT and ferrite phase. In addition, sharply grown up permittivity at lower frequency for 30 wt% ferrite composites was due to Maxwell–Wagner interfacial polarization among randomly oriented plate like BT and polyhedral-like ferrite phases12,32 or electrical charge depletion33 between two phases. It was observed that composites having 30 wt% ferrite phase stood lower permittivity at higher frequency. However, the value of permittivity of the composite systems either increases or decreases with increase in ferrite concentration due to involvement of Maxwell–Wagner affect, as three systems have different microstructures.12,31,32,34

Dielectric loss is also one of the important parameter and thus was studied for the BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems at room temperature. Fig. 5 shows the loss (tan[thin space (1/6-em)]δ) response with frequency for BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems. Dielectric loss is usually dependent on the dielectric phase and percentage of dielectric phase in the BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composites. In addition loss is also dependent on the connectivity of the dielectric phase. Also, loss is inversely proportional to the dielectric percentage in the composites.35 So, 20 wt% ferrite based BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composites showing low loss as compared 30 and 40 wt% ferrite based composites. However, maximum loss was varies in between 0.83 to 1.37 in these composite systems. It was observed that the loss decreases with frequency having a hump type response prominent in cobalt and zinc ferrite based composite systems. This response in the composite can be attributed to the resonance of applied frequency with the hopping mechanism between Fe2+ and Fe3+ ions.29


image file: c5ra16742f-f5.tif
Fig. 5 Dielectric loss as a function of frequency for BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems.

Polarization responses as a function of electric field of these composites are shown in Fig. 6. It was observed that the responses of PE loop in the BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composites deviated from the ideal ferroelectric loop due to the individual phase morphologies as well as connection of BT phase in the composite systems. The particular 30 or 40 wt% ferrite based composite systems appear in oval shape characteristics of a lossy capacitor due to field discharge by conductive ferrite phase.30,36 However, 20 wt% ferrite based BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems shows near ferroelectric type behavior. Polarization (at maximum field) and coercivity of all composites are given in Table 1. The polarization of these composites varies in between 1.2 to 10.8 μC cm−2 and coercivity varies in between 4 to 16 kV cm−1 depending on the ferrite type and percentage.


image file: c5ra16742f-f6.tif
Fig. 6 Polarization as function of electric field for BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems.
Table 1 Coercivity (Ec), polarization (P) (at maximum field), coercivity (Hc) and magnetization (M) of BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems
Composites Coercivity Ec (kV cm−1) Polarization P (μC cm−2) Coercivity Hc (kOe) Magnetization (M) at 4 kOe (emu g−1)
6BT$4CF 16 6.5 0.305 91.7
7BT$3CF 11.5 8.4 0.325 89.8
8BT$2CF 5 4.4 0.262 69.5
6BT$4ZF 4 10.8 0.309 73
7BT$3ZF 13 2.3 0.315 65
8BT$2ZF 5 3.8 0.291 64
6BT$4CZF 5.6 1.2 0.175 90.8
7BT$3CZF 16 2.6 0.203 84
8BT$2CZF 1.7 2.5 0.184 70

Similarly, magnetization as a function of magnetic field of BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems was analyzed. Magnetization and coercivity data of BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems are given in Table 1. M–H loop of all composites are look alike. However, the typical M–H loop of 30 wt% ferrite composites are shown in Fig. 7.


image file: c5ra16742f-f7.tif
Fig. 7 M–H loop of 30 wt% ferrite based BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems.

It was observed that BT[thin space (1/6-em)]:[thin space (1/6-em)]CF and BT[thin space (1/6-em)]:[thin space (1/6-em)]CZF composites are ferromagnetic in nature due to the magnetic characteristics of CF or CZF. However, the presence of hard magnetic phase of BaFe12O19 in the BT[thin space (1/6-em)]:[thin space (1/6-em)]ZF composites led to behave as ferromagnetic. Also, all these composites are ferromagnetic with non-saturating in nature due to the presence of different morphologies of BT phase, which act as a pinning center.14 The pinning effect clearly indicates the strong mechanical interaction between the magnetic and non-magnetic phase.14 From Table 1, it was observed that the magnetization (at 4.2 kOe) of the composites decreases with the increase in BT addition,13,34,37,38 due to the reduced magnetic moments per unit volume.30 Coercivity of the BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems depend on the ferrite concentration as well as the microstructure. In these composite systems, the coercivity varies in between 175 Oe to 325 Oe. However, the 30 wt% ferrite based composites have higher coercivity than other ferrite based composites due to pinning effect from plate-like morphologies of BT.

Generally, magneto-capacitance response in the BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite based composites originates from the mechanical coupling between ferromagnetic and ferroelectric phases present in the composites. Extrinsic parameters like magnetic/ferroelectric percentage and microstructure plays a significant role for enhancement of magneto-capacitance response.15 In the present study, the variation in microstructure of BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems motivated to explore the magneto-capacitance response. So, in these composite systems, percentage change in magneto-capacitance response as a function of magnetic field was measured and shown in Fig. 8. It was observed that the magneto-capacitance increases with increase in magnetic field and saturate at ∼2 K Oe. Both cobalt and zinc ferrite based composites followed the trend of increasing magneto-capacitance response with increase in percentage of ferrite. In addition, both cobalt and zinc ferrite based composites show negative magneto-capacitance response. However, cobalt–zinc ferrite based composite shows both negative (for 30 wt% ferrite) and positive (for 20 and 40 wt% ferrite) magneto-capacitance response.


image file: c5ra16742f-f8.tif
Fig. 8 Magneto-capacitance as function of magnetic field for BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems.

To explore further, magnetoimpedance [MI = (Z′(H) − Z′(O))/Z′(O)] values (at magnetic field of 2.68 kOe) as a function of frequency of these composite systems were determined and shown in Fig. 9. Also for better comparison, magneto-capacitance as a function of frequency of these BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems are presented in Fig. 10. By considering BT[thin space (1/6-em)]:[thin space (1/6-em)]CF composites, the magnetoimpedance behavior was found to be frequency dependent for all compositions. However, 7BT$3CF composite have nearly independent of frequency at lower frequency range (i.e. 42 Hz to ∼1 kHz). Also, the relaxation behavior was clearly seen in the cobalt ferrite based compositions particularly for 20 and 40 wt% ferrite based composites by observing peaks at 100 Hz and also at 1 M Hz. While, analyzing magnetocapacitance response of cobalt ferrite based composites in Fig. 10 at lower frequency range, it was revealed that the magnetocapacitance response was mainly due to involvement of magneto-resistance for particularly 20 and 40 wt% cobalt–ferrite based composites, whereas, the magnetocapacitance response in 30 wt% cobalt ferrite composite was due to the contribution of magnetostriction of CF phase in BT matrix. Also at lower frequency, 6BT$4CF composite was higher value impedance, whereas, 8BT$2CF composite shows lower impedance. Comparing with Fig. 10, the magneto-capacitance value was higher for 6BT$4CF composite and lower for 8BT$2CF composite. This indicates that the magnetoimpedance and magnetocapacitance are inverse with each other at lower frequency range. However, at higher frequency, the magnetoimpedance was found to be frequency dependent for BT[thin space (1/6-em)]:[thin space (1/6-em)]cobalt ferrite composite systems. But, magnetocapacitance behavior decreases and also frequency independent towards higher frequency. This suggests that the frequency independent magnetocapacitance behavior is due to insufficient time for charge carriers to respond to the applied field. Similarly, decreasing magneto-capacitance towards higher frequency is due to cancellation of magnetoresistance and M–W affect.9 The above discussion was also applicable for BT[thin space (1/6-em)]:[thin space (1/6-em)]ZF and BT[thin space (1/6-em)]:[thin space (1/6-em)]CZF composite systems. In 30 and 40 wt% ferrite based BT[thin space (1/6-em)]:[thin space (1/6-em)]ZF and BT[thin space (1/6-em)]:[thin space (1/6-em)]CZF composite systems have nearly frequency independent magnetoimpedance response at lower frequency as well as higher frequency range. However, 20 wt% ferrite based BT[thin space (1/6-em)]:[thin space (1/6-em)]ZF and BT[thin space (1/6-em)]:[thin space (1/6-em)]CZF composite systems have frequency dependent magnetoimpedance behavior having peak at ∼1 kHz. Comparing Fig. 9 and 10, it was observed that BT[thin space (1/6-em)]:[thin space (1/6-em)]ZF and BT[thin space (1/6-em)]:[thin space (1/6-em)]CZF composites having 30 and 40 wt% ferrites shows frequency independent magneto-capacitance response which suggest that the magnetocapacitance originates from magnetostriction of ferrite phase. However, even small response of magnetocapacitance for 20 wt% ferrite based BT[thin space (1/6-em)]:[thin space (1/6-em)]ZF and BT[thin space (1/6-em)]:[thin space (1/6-em)]CZF composites have maximum contribution from magnetoresistance affect.


image file: c5ra16742f-f9.tif
Fig. 9 Magneto-impedance as function of frequency for BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems.

image file: c5ra16742f-f10.tif
Fig. 10 Magneto-capacitance as function of frequency for BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems.

Further to support the origin of magnetocapacitance response in the present composite system, Cole–Cole graph was plotted for all composite systems without and with magnetic field (at 2.68 kOe) and is shown in Fig. 11. In case of BT[thin space (1/6-em)]:[thin space (1/6-em)]CF composite systems all compositions show a change in resistance with application of magnetic field except for the composite 7BT$3CF. It further suggests that the magnetocapacitance behavior of the particular 7BT$3CF composites originates from magnetostriction of CF phase. Whereas, the magneto-capacitance behavior of both 8BT$2CF and 6BT$4CF composite are due to magnetoresistance affect. A small change in resistance was observed in both 30 and 40 wt% ferrite based composites of BT[thin space (1/6-em)]:[thin space (1/6-em)]ZF and BT[thin space (1/6-em)]:[thin space (1/6-em)]CZF, whereas, a quite large change in resistance with application of magnetic field was observed in the particular 20 wt% Zn– and Co–Zn ferrite based composite systems. This further support that the magnetocapacitance behavior of 30 and 40 wt% ferrite based BT[thin space (1/6-em)]:[thin space (1/6-em)]ZF and BT[thin space (1/6-em)]:[thin space (1/6-em)]CZF composite systems are mainly due to magnetostriction, whereas, magnetocapacitance behavior of 20 wt% ferrite based BT[thin space (1/6-em)]:[thin space (1/6-em)]ZF and BT[thin space (1/6-em)]:[thin space (1/6-em)]CZF composite systems are due to magnetoresistance.


image file: c5ra16742f-f11.tif
Fig. 11 Cole–Cole plots of BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems without and with magnetic field.

Further, in order to understand the grain and grain boundary resistance, Cole–Cole graph was fitted with an equivalent circuit of R(Q1R1)(Q2R2) with the experimental data. It was found that for 30 and 40 wt% ferrite based BT[thin space (1/6-em)]:[thin space (1/6-em)]CF, BT[thin space (1/6-em)]:[thin space (1/6-em)]ZF and BT[thin space (1/6-em)]:[thin space (1/6-em)]CZF composite, the grain boundary resistance and capacitance remains nearly constant without and with application of magnetic field. However, for 20 wt% ferrite based composites, the grain boundary resistance and capacitance increases with the application of magnetic field. Hence, the samples with 20% ferrite phase show a wide deviation of impedance in Cole–Cole plot.

The origin of magneto-capacitance behavior in the present BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems can be explained in different ways: first, induced strain in the magnetic material due to applied magnetic field can modify the magneto-capacitance of the composite by mechanical coupling.14 Second, according to the Catalan,33 the interfacial polarization effect in magneto-dielectric composite systems can also give magneto-capacitance response based on the resistance of the conducting grain or grain boundary with application of magnetic field. In addition, the microstructure or morphology of BT/ferrite phase may also effect the magneto-capacitance response that depend on the interfacial interaction between the dielectric and magnetic phases present in the composite.3,4,14,38

The positive or negative nature of magnetocapacitance in the present BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems strongly depend on the magnetostriction of ferrite phase, magnetoresistance of grain or grain boundary as well as morphology of BT phase. It was suggested that the negative magnetostriction of zinc ferrite led to show negative magnetocapacitance3,8 in zinc–ferrite based composite system. However, negative magnetostriction of cobalt–zinc ferrite led to show positive magnetocapacitance in cobalt–zinc-ferrite based composite system.14 But, the negative magnetostriction of cobalt ferrite led to show positive or negative magnetocapacitance in cobalt–ferrite based composite systems.1,10,15,38 So, it is difficult to narrow down the link between sign of magnetostriction and magnetocapacitance in the magneto-dielectric composite system, however, the collected data is given in Table 2. In addition, core-dominated magnetoresistance and interface-dominated magnetoresistance give positive and negative magneto-capacitance, respectively.33 Also, in the present system, it was found that the magnetoresistance or magnetostriction induced magnetocapacitance strongly depends on the composition of ferrite phase. The negative response of magneto-capacitance in both cobalt and zinc ferrite based composite systems was due to strong interaction between plate-like morphology of BT and polyhedral ferrite phase at the interface. Similar observation was also observed in most of the literatures and are well discussed based on the interfacial mechanical interaction or interface dominated magneto-resistance between the dielectric and magnetic phases.3,33,38 However, both positive and negative magneto-capacitance response in BT[thin space (1/6-em)]:[thin space (1/6-em)]CZF composites are due to the involvement of magnetoresistance or magnetostriction along with microstructural effect in which randomly oriented plate-like morphology of BT modifies the magneto-capacitance response. The values of magneto-capacitance in these composite systems are found to be enhanced, when compared with the literature data as given in Table 3.

Table 2 Sign of magnetostriction and direction of magnetocapacitance in the magneto-dielectric composite system collected from the literatures
Sl. no. Composite system Magnetocapacitance direction Proposed sign of magnetostrction Ref.
1 Co0.65Zn0.35Fe2O4–PbZr0.52Ti0.48O3 Positive Negative 4 and 14
2 BaTiO3–ZnFe2O4 Negative Negative 4 and 8
3 [Ba(Sn0.3Ti0.7)O3]0.8–[CoFe2O4]0.2 Positive Negative 1
4 BaTiO3–CoFe2O4 Negative Negative 15

Table 3 Maximum magnetocapacitance (%) values were collected from literature data and compare with the present system
Sl. no. Composite system Magnetocapacitance % Composite type Ref.
1 BaTiO3–CoFe2O4 −4.5 at 2.1 Tesla Core and shell bulk composites 15
2 (X)Co0.65Zn0.35Fe2O4–(1 − X)PbZr0.52Ti0.48O3 ∼1.1 at 7 Tesla for X = 0.3 Particulate bulk composites 14
3 BaTiO3–ZnFe2O4 ∼−0.75 at 4 Tesla Thin films 5
4 BaTiO3–CoFe2O3 2.5 at 75 kOe Thin films 6
5 (X)BaTiO3–(1 − X)CoFe2O3 7.5 at 1.3 kOe for X = 0.5 Particulate bulk composites 7
6 BaTiO3–ZnFe2O3 ∼−1.3 at 10 kOe Core and shell bulk composites 8
7 BaTiO3–CoFe2O3 ∼3.8 at 7 kOe Core and shell bulk composites 9
8 (1 − X)BaTiO3–XCoFe2O4 −3.9 at 4.5 × 105 A m−1 Particulate bulk composites 38
Present system (X)BaTiO3–(1 − X)CoFe2O3 −9 at 2.68 kOe for X = 0.6 Particulate bulk composites  
(X)BaTiO3–(1 − X)Co0.5Zn0.5Fe2O3 −1.5 at 2.68 kOe for X = 0.8
1.5 at 2.68 kOe for X = 0.7
(X)BaTiO3–ZnFe2O3 −7 at 2.68 kOe for X = 0.6

Conclusions

Composite of BT[thin space (1/6-em)]:[thin space (1/6-em)]CF, BT[thin space (1/6-em)]:[thin space (1/6-em)]ZF and BT[thin space (1/6-em)]:[thin space (1/6-em)]CZF having 20, 30 and 40 wt% ferrite were successfully prepared via conventional solid-state mixing route using auto-combustion derived powders. The composite microstructure consists of plate-like (prominent in 7BT[thin space (1/6-em)]:[thin space (1/6-em)]3 CF/ZF/CZF composite systems) as well as agglomerated spherical-like morphologies of BT and polyhedral-like morphology of ferrites. Frequency dependence dielectric behavior in these composites was well explained from the consideration of microstructural features such as distribution of phases, their amount and characteristics. Field discharge by conductive ferrite phase was found to be responsible for lossy behavior observed in PE loop. The pinning of BT phase in these composite systems shows non-saturating behavior of MH characteristics. The origin of magnetocapacitance response in these composite systems was well-correlated using magnetoimpedance against frequency and Cole–Cole graph. It was found that magneto-capacitance response of 7BT$3CF, 7BT$3ZF, 7BT$3CZF, 6BT$4ZF and 6BT$4CZF composite arises due to magnetostriction of ferrite phase. However, the magnetocapacitance response of 8BT$2CF, 6BT$4CF, 8BT$2ZF and 8BT$2CZF composite was due to contribution of magneto-resistance. Involvement of either magnetoresistance and or magnetostriction along with morphology of BT phase in BT[thin space (1/6-em)]:[thin space (1/6-em)]ferrite composite systems have a role to tune as well as enhance the magneto-capacitance response in either positive or negative way depending on the percentage of ferrite phase.

References

  1. M. N. Ul-Haq, T. Yunus, A. Mumtaz, V. V. Shvartsman and D. C. Lupascu, J. Alloys Compd., 2015, 640, 462–467 CrossRef.
  2. M. Stingaciu, P. G. Reuvekamp, C.-W. Tai, R. K. Kremer and M. Johnsson, J. Mater. Chem. C, 2014, 2, 325–330 RSC.
  3. K. C. Verma, S. K. Tripathy and R. K. Kotnala, RSC Adv., 2014, 4, 60234–60242 RSC.
  4. G. Srinivasan, E. T. Rasmussen and R. Hayes, Phys. Rev. B: Condens. Matter Mater. Phys., 2003, 67, 014418 CrossRef.
  5. M. Lorenz, M. Ziese, G. Wagner, J. Lenzner, C. Kranert, K. Brachwitz, H. Hochmuth, P. Esquinazi and M. Grundmann, CrystEngComm, 2012, 14, 6477–6486 RSC.
  6. I. Fina, N. Dix, L. Fàbrega, F. Sánchez and J. Fontcuberta, Thin Solid Films, 2010, 518, 4634–4636 CrossRef CAS.
  7. M. Rafique, S. Q. Hassan, M. S. Awanb and S. Manzoor, Ceram. Int., 2013, 39, S213–S216 CrossRef CAS.
  8. S. Singh, N. Kumar, R. Bhargava, M. Sahni, K. Sung and J. H. Jung, J. Alloys Compd., 2014, 587, 437–441 CrossRef CAS.
  9. M. M. Selvi, P. Manimuthu, K. S. Kumar and C. Venkateswaran, J. Magn. Magn. Mater., 2014, 369, 155–161 CrossRef CAS.
  10. Y. Q. Dai, J. M. Dai, X. W. Tang, K. J. Zhang, X. B. Zhu, J. Yang and Y. P. Sun, J. Alloys Compd., 2014, 587, 681–687 CrossRef CAS.
  11. L. Curecheriua, P. Postolache, V. Buscaglia, N. Horchidan, M. Alexe and L. Mitoseriu, Phase Transitions, 2013, 86(7), 670–680 CrossRef.
  12. A. Testino, L. Mitoseriu, V. Buscaglia, M. T. Buscaglia, I. Pallecchi, A. S. Albuquerque, V. Calzona, D. Marré, A. S. Siri and P. Nanni, J. Eur. Ceram. Soc., 2006, 26, 3031–3036 CrossRef CAS.
  13. S. Agarwal, O. F. Caltun and K. Sreenivas, Solid State Commun., 2012, 152, 1951–1955 CrossRef CAS.
  14. P. R. Mandal and T. K. Nath, J. Alloys Compd., 2014, 599, 71–77 CrossRef CAS.
  15. K. Raidongia, A. Nag, A. Sundaresan and C. N. R. Rao, Appl. Phys. Lett., 2010, 97, 062904–62913 CrossRef.
  16. D. Zhou, G. Jian, Y. Zheng, S. Gong and F. Shi, Appl. Surf. Sci., 2011, 257, 7621–7626 CrossRef CAS.
  17. L. Zhang, J. Zhai, W. Mo and X. Yao, Solid State Sci., 2011, 13, 321–325 CrossRef CAS.
  18. L. Zhang, J. Zhai, W. Mo and X. Yao, Solid State Sci., 2010, 12, 509–514 CrossRef CAS.
  19. I. Kagomiya, Y. Hayashi, K. Kakimoto and K. Kobayashi, J. Magn. Magn. Mater., 2012, 324, 2368–2372 CrossRef CAS.
  20. L. Zhang, J. Zhai, W. Mo and X. Yao, Mater. Chem. Phys., 2009, 118, 208–212 CrossRef CAS.
  21. H. Yang, G. Zhang, Y. Lin and F. Wang, Mater. Lett., 2015, 157, 99–102 CrossRef CAS.
  22. J. Nie, G. Xua, Y. Yangb and C. Cheng, Mater. Chem. Phys., 2009, 115, 400–403 CrossRef CAS.
  23. Y. Deng, J. Zhou, D. Wuc, Y. Du, M. Zhang, D. Wang, H. Yu, S. Tang and Y. Du, Chem. Phys. Lett., 2010, 496, 301–305 CrossRef.
  24. S. H. Xiao, W. F. Jiang, L. Y. Li and X. J. Li, Mater. Chem. Phys., 2007, 106, 82–87 CrossRef CAS.
  25. C. Heck, Magnetic Materials and Their Applications, Butterworths, London, 1974 Search PubMed.
  26. V. corral-flores, D. Bueno-Baques, D. Carrilo-Flores and J. A. Matutes-Aquino, J. Appl. Phys., 2006, 99(8), 08J5031 CrossRef.
  27. G. V. Duong, R. Groessinger and R. S. Tirtelli, IEEE Trans. Magn., 2006, 42(10), 3611–3613 CrossRef CAS.
  28. G. V. Duong, R. Groessinger and R. S. Tirtelli, J. Magn. Magn. Mater., 2007, 310(2), e361–363 CrossRef CAS.
  29. H. Zhenga, W. J. Wenga, G. R. Hana and P. Y. Du, Ceram. Int., 2015, 41, 1511–1519 CrossRef.
  30. A. khamkongkaeo, P. Jantaratana, C. Sirisathitkul, T. yamwong and S. Maensiri, Trans. Nonferrous Met. Soc. China, 2011, 21, 2438–2442 CrossRef CAS.
  31. Z. Yu and C. Ang, J. Appl. Phys., 2002, 91(2), 794–797 CrossRef CAS.
  32. H. Yang, H. Wang, L. Hea and X. Yaoa, Mater. Chem. Phys., 2012, 134, 777–782 CrossRef CAS.
  33. G. Catalan, Appl. Phys. Lett., 2006, 88, 102902–102903 CrossRef.
  34. H. Zheng, L. Li, Z. Xu, W. Weng, G. Han, N. Ma and P. Du, J. Appl. Phys., 2013, 113, 044101–044108 CrossRef.
  35. R. Zhang, C. Deng, L. Ren, Z. Li and J. Zhou, Mater. Res. Bull., 2013, 48, 4100–4104 CrossRef CAS.
  36. M. Ghidini, F. Maccherozzi, X. Moya, L. C. Phillips, W. Yan, J. Soussi, N. Métallier, M. E. Vickers, N.-J. Steinke, R. Mansell, C. H. W. Barnes, S. S. Dhesi and N. D. Mathur, Adv. Mater., 2015, 27, 1460–1465 CrossRef CAS PubMed.
  37. L. Mitoseriu, I. Pallecchi, V. Buscaglia, A. Testino, C. E. Ciomaga and A. Stancu, J. Magn. Magn. Mater., 2007, 316, e603–e606 CrossRef CAS.
  38. Y. Sen, J. Sun, L. Li, Y. Yao, C. Zhou, R. Su and Y. Yang, J. Mater. Chem. C, 2014, 2, 2545–2551 RSC.
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