Structural, dielectric and magnetic studies of ferrite-ferroelectric composites

Journal Pre-proof Structural, dielectric and magnetic studies of ferrite-ferroelectric composites S. Abdul Khader, Asiya Parveez, Arka Chaudhuri, T. Sankarappa PII:

S0921-4526(19)30568-X

DOI:

https://doi.org/10.1016/j.physb.2019.411675

Reference:

PHYSB 411675

To appear in:

Physica B: Physics of Condensed Matter

Received Date: 16 January 2019 Revised Date:

28 August 2019

Accepted Date: 31 August 2019

Please cite this article as: S.A. Khader, A. Parveez, A. Chaudhuri, T. Sankarappa, Structural, dielectric and magnetic studies of ferrite-ferroelectric composites, Physica B: Physics of Condensed Matter (2019), doi: https://doi.org/10.1016/j.physb.2019.411675. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.

Structural, Dielectric and Magnetic Studies of Ferrite-Ferroelectric Composites S.Abdul Khader*1, Asiya Parveez 2, Arka Chaudhuri3 and T.Sankarappa4 1

Department of Physics, Govt.Science College, Chitradurga-585106, Karnataka, India.

2

Department of Materials Science, University of Mysore, Mysore-570005, Karnataka.

3

Department of Applied Science, Haldia Institute of Technology, Haldia-721657, India 4

Department of Physics, Gulbarga University, Gulbarga-585106, Karnataka, India

*Corresponding author: [email protected]

Abstract. The composites of ferrite-ferroelectric system (x) Mg0.2Cu0.5Zn0.3Fe2O4+ (1-x) BaTiO3 (x=15%, 30% and 45%) were synthesized by sintering the mixtures of ferroelectric BaTiO3 (BTO) and ferrite component Mg0.2Cu0.5Zn0.3Fe2O4 (MCZF). Ferrimagnetic MCZF was prepared using auto-combustion method where as ferroelectric BTO was procured commercially from Sigma-Aldrich. The presences of two phases in magneto-electric composites were probed by Xray diffraction (XRD) studies. The peaks observed in the XRD spectrum indicated spinel cubic structure for MCZF ferrite and tetragonal perovskite structure for BTO and, both spinel and pervoskite structures for synthesized composites. Surface morphology of the samples has been investigated using Field Emission Scanning Electron Microscope (FESEM). Frequency dependent dielectric properties of synthesized composites were measured from 100 Hz to 1 MHz at room temperature (RT) using HIOKI LCR HI-TESTER. The dielectric dispersion is observed at lower frequencies for the synthesized ME composites. The magnetic properties of synthesized composites were analyzed using a Vibrating Sample Magnetometer. It is observed that the composites exhibited magnetic hysteresis with narrow loops indicating the magnetic ordering in the composites. All the measurements were carried out at room temperature.

Keywords: ferroelectric; magnetoelectric; polarization; spinel; small polarons; tangent loss

1

1. Introduction Composites containing two individual phases, one ferroelectric and the other ferrri-magnetic exhibit unique and novel magneto-electric phenomena that are facilitated by elastic interactions via strain [1–5]. Magneto-electric (ME) composites, consists of physically separated magnetic and electric order phases. These composites show coupling with orders of magnitude larger than those found in single phase materials at room temperature [3]. ME coupling in composites occur extrinsically in three different ways mediated through strain, charge carrier and spin exchange. Among these mechanisms, the strain mediated coupling will be discussed. The strain mediated ME effect in composites is a product tensor property and results from the elastic coupling between piezoelectric and magneto-strictive phases. In Direct ME coupling, the applied magnetic field generates strain in magnetic phase through the magnetostriction effect, and this strain is transferred to the ferroelectric phase resulting in an electric displacement or a dielectric polarization through the piezoelectric effect. ME materials have evolved from single phase compounds to particulate composites, to laminated composites, and finally to micro and nano-thin films. The difficulties associated with uniting electric and magnetic orderings in a single phase material have been circumvented by forming multi-phase ME composites of ferromagnetic and ferro-electric components that can be electromagnetically coupled by stress mediation [6]. The ME composites have been exploited as sensors, waveguides, switches, phase invertors, modulators, etc. [7].

Mg0.2Cu0.5Zn0.3Fe2O4 (MCZF) being an important soft magnetic materials because of its high initial magnetic permeability, saturation magnetization and low core losses [8-10]. The selection of a suitable combination of ferromagnetic and ferroelectric materials to achieve better ME effect is a challenging task. In order to achieve better ME effect, the piezomagnetic coefficient of ferrite phase and the piezoelectric coefficient of ferroelectric phase must be high. The resistivity of both the phases should be comparable and the mechanical coupling between the two phases is perfect [9].

In the present work, MCZF as piezomagnetic material and BaTiO3 (BTO) as a piezoelectric material were choosen and composites were prepared and studied the effect of composition and frequency on the dielectric and magnetic properties of these composites. The study also offered

2

valuable information on the behavior of localized electric charge carriers which in turn helps in understanding magneto electric effect [10-12].

2. Experimental Procedure The Mg0.2Cu0.5Zn0.3Fe2O4 nano ferrite (MCZF) powder has been prepared by combustion method, using stoichiometric compositions of corresponding metallic nitrates as oxidizers and citric acid as fuel. BaTiO3 (BTO) was procured commercially from sigma Aldrich. The ME composites were prepared by thoroughly mixing MCZF and BTO powders in required molar proportions and sintered at 1343K for 6 hrs and were cooled slowly to room temperature. These sintered powders were grinded and pressed in the form of pellets of 10 mm diameter and 1-2 mm thickness. The pellets were again sintered at 1388K for 4 hrs and cooled to room temperature. The synthesized ME composites, (MCZF)x(BTO)1-x with x = 15%, 30% & 45% have been labeled as MCBT1, MCBT2 and MCBT3 respectively. The composites were prepared in ferroelectric-rich regions [13].

The presence of constituent phases in the composites and the crystal structure of constituent phases and their composites were determined by XRD studies using Bruker AXS D8 Advance X-ray diffractometer (λ=1.5418 Å ). Surface morphology of the samples has been investigated using Field Emission Scanning Electron Microscope (ULTRA 55). Magnetic studies were performed using a Vibrating Sample Magnetometer (Lake Shore, USA Model: 7404).

The Parallel capacitance and dissipation factor, tan of the test sample as a function of frequency in the range 100 Hz-1MHz was studied using a precision LCR meter (Hioki make LCR Hi-Tester 3250). The dielectric constant (') and dielectric loss factor ('') were determined using the formulae [14-16].

ε' = Ct/ε0A

(1)

ε''= ε' tan δ

(2)

Where, t is the thickness and A the area of the pellet. The ac conductivity ,σac was determined from dielectric data using the standard relation, σac =ωε0ε"

(3)

3

Where, ε0 is the vacuum permittivity and ω =2πf with f being frequency.

3. Results and discussion 3.1 Structure and Morphological Studies The XRD patterns of pure MCZF, BTO and MCBT1 were shown in Fig.1. Similar pattern were observed in case of MCBT2 and MCBT3. The diffraction patterns of composites showed the presence of the both ferrite and ferroelectric phases. The ferrite phase BTO showed a cubic spinel structure with a=8.36 Å and ferroelectric phase exhibited perovskite tetragonal structure with a=4.02Å, c=4.04 Å (c/a=1.004). The lattice parameters of the constituent phases are described to be same for MCBT1, MCBT2 and MCBT3. As the concentration or percentage of ferrite content in ME composites increases, in diffractogram the reflection corresponding to miller indices (311) peak height which corresponds to ferrite phase also increases where as the reflection corresponding to miller indices (101) peak height which is related to ferroelectric phase decreases [17]. The scanning electron micrographs of doped ME composites namely; MCBT1, MCBT2 and MCBT3 are shown in Fig.2. Each sample exhibits well defined randomly oriented grains with minimum pores. The shape and distribution of grains confirms the polycrystalline nature of the sintered sample.

4

FIGURE 1. XRD Pattern for pure powders of Mg0.2Cu0.5Zn0.3Fe2O4 (MCZF), BaTiO3 (BTO) and (x) MCZF + (1-x) BTO ME composites

5

FIGURE 2. FESEM micrographs for powders of (a) MCZF, (b) MCBT1 (c) MCBT2 and (d) MCBT3 composites.

3.2 Dielectric properties The variation of dielectric constant (ε'), dielectric loss factor (ε") and ac conductivity (σac) with frequency at room temperature for the sintered ME composites is shown in Fig.3. From the Fig.3 (a) it is clear that ε' decreases steeply at lower frequencies and remains constant at higher frequencies. The variation of dielectric constant with applied frequency is due to charge transport relaxation. This dielectric dispersion is attributed to Maxwell and Wagner [18] type of interfacial polarization, which occurs when two phases of different conductivities are connected to each other, giving rise to uncompensated charges at the interface separating these ferroelectric-ferrite phases. The dielectric constant is a combined effect of dipolar, electronic, ionic and interfacial polarizations. Since ionic polarization is expected to decrease with frequency, the measured

6

ε' also decreased with frequency. The large values of ε' can be associated with space charge polarization and inhomogeneous dielectric structure. These inhomogeneties arise from impurities, grain structure and pores [19]. In case of composites, the high values of dielectric constant are ascribed to the fact that ferroelectric grains are surrounded by non-ferroelectric grains similar to that observed in relaxor ferroelectric materials [19].

In ME composites, ferroelectric phase is more resistive than ferrite phase, the increase in ferrite concentration leads to the decrease in the resistivity of ME composites. The presence of Fe3+ and Fe2+ ions has rendered ferrite materials dipolar. By electron exchange between Fe+2 and Fe+3, the local displacement of electrons in the direction of the applied field occurs and these electrons determine the dielectric polarization. This dielectric polarization decreases with increasing frequency and at high frequency the electron exchange between Fe+2 and Fe+3 cannot follow the quick changes of alternating field hence reaches the constant value. In composites, the higher value of the dielectric constant at lower frequencies is associated with heterogeneous conduction of the two distinct phases with different resistivities such as ferroelectric and ferrite phases [20, 21], but sometimes, the polaron hopping mechanism results in electronic polarization contributing to low frequency dispersion.

The variation of ε", in case of composites is similar to that of variation of ε' with frequency, ω. This loss factor is attributed to domain wall resonance [22]. At higher frequencies, the losses are reduced and the dipoles contribute to the polarization. At these frequencies, the dielectric losses are low due to the inhibition of domain wall motion.

In order to understand the conduction mechanism and type of polarons responsible for conduction, ac conductivity, σac were estimated as per σac= ωε0ε" [23], with ε0 is the permittivity of free space and ω=2πf.

7

The variation of σac with frequency, ω, is shown in Fig.3 (c) for all the composite samples. The plots are linear for almost entire range of frequency except at very low frequency. Linear variation of σac with frequency indicates that the conduction occurs by the hopping of charge carriers between the localized states. The frequency and composition dependent conduction is attributed to small polarons. These results are similar to that reported by other workers [24-25]. However, the slight decrease in conductivity at lower frequencies from (100 Hz- 1 kHz) may be attributed to conduction by mixed polarons because of the non linearity of the curves at low frequencies [26]. At lower frequencies in all the composites, there is a slight non-linearity at a range of kHz frequency and deviates from the classical Jonsher relationship [27] and some researchers also reported the similar conductivity phenomenon in NFO-BTO composites by the superposition of a double power law [28]. They associated different processes with short range polaron hopping at low frequencies and a localized hopping of the carriers inside the grains at higher frequencies.

8

FIGURE 3. Variation of (a) dielectric constant, ε' with frequency, ln (ω), (b) dielectric loss, ε" with frequency, ln (ω) and (c) conductivity, ln (σac) with frequency, ln (ω) at RT.

9

3.3 Magnetic studies The magnetization, M, as a function of applied field, H, was measured at RT for the proposed MCZF-BT ME composites. Fig.4 Shows the magnetic hysteresis loops for pure Mg0.2Cu0.5Zn0.3Fe2O4 (MCZF) and doped ME composites. All the ME composites confirmed magnetic ordering in them at room temperature and exhibited saturated typical ferromagnetic behavior. Coercive field, Hc, saturation magnetization, Ms, remanent magnetization, Mr, were determined from the hysteresis loops and they are listed in Table.1. The values of Ms and Mr were found to increase with increase in ferrite concentration. The increase in Ms is because of the contribution from ferrite grains, as these ferrite grains will act as centers of magnetization and the saturation magnetization of composites is the vector sum of all these individual ferrite grain contributions [29-42].

FIGURE 4. Plots of magnetization, M versus magnetic field, H for MCZF-BTO system.

Table 1. Magnetic parameters derived from M-H loops for MCZF-BTO ME composites.

Sample MCZF MCBT1 MCBT2 MCBT3

Remanent Saturation magnetization. magnetization. Ms (emu/g) Mr (emu/g) 53.6 1.76 7.67 0.28 17.22 0.22 25.49 0.65

10

Coercive Field. Hc (Oe) 20 14 11.5 12.8

4. Conclusions Ferrite-ferroelectric composites of MCZF and BTO were successfully prepared. XRD patterns, FESEM micrographs reveal the presence of both ferrite and ferroelectric phase with no other impurity phases. The frequency dependant dielectric constant shows the usual dielectric dispersion behavior for all the composites. The ac conductivity measurements suggest that the conduction is due to small polaron hopping mechanism. The composites exhibit magnetic hysteresis loops at room temperature under applied magnetic electric field.

References 1. 2. 3. 4. 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

W.Eerenstein, N.D.Mathur and J.F.Scott, Nature Reviews. 442 (2006), 759–765. Ortega,N.,Kumar, A.Scott, J.F Katiyar, R.S, J.Phys Cond.Matter 27 (2015),504002. Martin, L.W, Ramesh. R, Acta Mater 60 (2012), 2449-2470. Fiebig.M, Jour.Phys D: Appl.Phy 38(2005), R123-R152. F.El. Kamel, P. Gonon, F. Jomni, B. Yangui, J. Eur. Ceram. Soc. 27 (2007), 3807 Srinivasan G,Annu.Rev.Mater.Res 40 (2010), 153-178. Nan,C-W., Li M, Huang J.H, Phys.Rev.B 63 (2001), 144415. J. Van den Boomgaard, D.R. Terrell, R.A.J. Born, J. Mater. Sci. 9 (1974), 1705. V.M. Petrov, M.I. Bichurin, G. Srinivasan, Tech. Phys. Lett. 30 (2004), 341. J.Van Suchtelen, Philips Res.Rep 27 (1972), 28. Harshe G, Dougherty, J.O, Newnham R.E, Int.J.Appl Electromagn.Mater 4 (1993), 145. Mazumdar S and Bhattacharyya G S, Mater. Res. Bull. 38(2003), 303 Ryu J, Carzo A V, Uchino K J and Kim H R, Japan. J. Appl. Phys. 40 (2001), 4948 Suchtelen J V, Philips Res. Rep. 27 (1972),28 Zhai J, Cai N, Shi Z, Lin Y and Nan C W, J. Phys. D: Appl. Phys. 37(2004), 823 Cho K-H, Priya S, Appl.Phy. Lett 98 (2011), 232904. Richa Sharma, Poonam Pahuja, R.P Tandon, Ceramics Int 40 (2014) 9027-36. K.W.Wagner,Ann.Phys 40 (1993) 818. Priya S, Islam R, Dong S, Viehland D, J.Electroceram 19 (2007), 149-166. M. Dawber, K. Rabe, J. Scott, Rev. Mod. Phys. 77 (2005) 1083 Ryu J, S. Priya, Uchino K, Kim H-E, J.Electroceramics 8 (2002), 107-119. C.M Kanamadi, G.S Rama Raju, H.K Yang, B.C Choi, J.Alloy Comp 479 (2009) 807. J. Jin, et al. Adv. Mater. 23 (33) (2011) 3853. S.Abdul Khader, N.V.Giridharan, T.Sankarappa, AIP:Conf.Proc 1728 (2016), 020529. S. Upadhyay, Devendrakumar, Omprakash, Bull. Mater. Sci. 19 (1996) 513. R.Grigalaitis, M.M Viatovic Petrovic, J.D Bobic, J.Banys, Ceramics. Int 40 (2014) 6165. A.K Jonscher, J.Mater.Sci 16 (1981)2037-2060. L.P Curecheriu, M.T Buscaglia, L.Mitoseriu, A.Ianculescu, P.Nanni, J.Appl.Phys 107 (2010) 104106. 29 R.C Kambale, P.A.Shaikh, K.Y Rajpure, Y.D Kolekar, Integ. Ferroelectrics 121 (2010). 30 S.Abdul Khader, T.Sankarappa, Materials Today Proceedings 3 (2016) 2547. 31 I.D. Mayergoyz, Mathematical Models of Hysteresis, Springer-Verlag, New York (1991).

11

32 33 34 35 36 37 38 39

Yogesh Kumar, K.L Yadav, Jyoti Shah, R.K Kotnala, Mater.Res.Exp 5 (2018) 085701. C.G. Koops, Phys. Rev. 83 (1951) 121. Mazumder S, Battacharyya G. S, Mater.Res Bull 38 (2003), 303-310. Nan C-W, Phy.Rev B 50 (1994), 6082-6088. Fawzi AS, Adv.in. Appl.Sci.Res 2 (2011) 577. J.Kulawik, D.Szwagierczak, P.Guzdek, Jour.Mag and Mag. Mats 324 (2012) 3052. Zolkepli, M.F.A. & Zainuddin Z, AIP Conference Proceedings (2015), 1678: 040014. Köferstein, R., Walther, T., Hesse, D. & Ebbinghaus, S.G., Jour. of Alloys and Compounds 638 (2015), 141-147. 40 Ravindar Tadi, Yong-Il Kim, Debasish Sarkar, Cheolgi Kim & Ryu, K.S. Jour. Mag and Mag. Materials 323 (2010), 564-658. 41 P.KRoy and J.Bera. Mat.Chem. Phys. 132 (2012), 354-357. 42 S. Y. Tan, S. R. Shannigrahi, S. H. Tan, & F. E. H. Tay, J.Appl.Phys., 103 (2008) , 094105.

12