Studies of Phase Transitions and Magnetoelectric Coupling in PFN

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Studies of Phase Transitions and Magnetoelectric Coupling in PFN-CZFO Multiferroic Composites Dhiren Kumar Pradhan, Venkata Sreenivas Puli, Shalini Kumari, Satyaprakash Sahoo, Proloy Taran Das, Kallol Pradhan, Dillip Kumar Pradhan, James F. Scott, and Ram S. Katiyar J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b10422 • Publication Date (Web): 30 Dec 2015 Downloaded from http://pubs.acs.org on January 3, 2016

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Studies of Phase Transitions and Magnetoelectric Coupling in PFN-CZFO Multiferroic Composites Dhiren K. Pradhan1,*, Venkata S. Puli2 , Shalini Kumari1 , Satyaprakash Sahoo1, Proloy T. Das3, Kallol Pradhan1, Dillip K. Pradhan4, J. F. Scott5, Ram S. Katiyar 1,* 1

Department of Physics and Institute of Functional Nanomaterials, University of Puerto Rico, San Juan-00936, PR, USA

2

Department of Mechanical Engineering,College of Engineering, University of Texas,El Paso, TX-79968,USA 3

Department of Physics, Indian Institute of Technology, Kharagpur-721302, India.

4

Department of Physics, National Institute of Technology, Rourkela-769008, India.

5

Department of Chemistry and Department of Physics, University of St. Andrews, St. Andrews KY16 ST, United Kingdom

*

Authors to whom correspondence to be addressed. Electronic mail: [email protected]

(Ram S. Katiyar), [email protected] (Dhiren K. Pradhan) Abstract We report studies of the ferroelectric and magnetic phase transition of (1-x) Pb(Fe0.5Nb0.5)O3 - x Co0.65Zn0.35Fe2O4 (x = 0.2) composite with emphasis upon the nature of magnetoelectric coupling at room temperature. The presence of all cationic elements with their required stoichiometry has been confirmed by SEM and XPS studies. The composite shows wellsaturated ferroelectric and ferromagnetic (multiferroic) behavior at room temperature. A ferroelectric-paraelectric phase transition has been confirmed from the temperature dependent dielectric spectra along with DSC and Raman spectroscopic studies. Antiferromagnetic, ferromagnetic and relaxor paramagnetic states have been observed in this composite. This

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composite shows strong bulk biquadratic magnetoelectric coupling at room temperature, which can be useful for potential multifunctional device applications. I.

Introduction

Multiferroic magnetoelectric materials - those which exhibit simultaneous ferroelectric and ferromagnetic behaviors and permit control and switching of the magnetic order parameter, magnetization M via electric field E, and polarization P with magnetic field H, have drawn significant interest in recent years because of their intriguing physical origin and great potential for multifunctional applications.1,2,3 Understanding the coupling of the ferroic (electric and magnetic) order parameters in multiferroics is a long-standing scientific challenge that is intimately linked to the spatial and temporal symmetries associated with charge and spin.1,2,4,5 Regarding the coupling between the order parameters, it has been proposed that the ME coupling may arise directly between electrical and magnetic order parameters or indirectly via lattice strain.1 Room-temperature single-phase multiferroic materials are very few in nature due to the frequent chemical incompatibility between magnetism and ferroelectricity.6,7,8 The magnetic and ferroelectric ordering in single-phase multiferroics often occur independently of each other, and as a result, the magnetoelectric coupling tends to be small.8,9 The rareness of room-temperature single-phase multiferroics, their low critical temperatures (ferroelectric/ferromgnetic) and/or weak ME coupling compounds have led researchers instead to the design and development of artificially composite structures.5,6,7,8 Increasing the magnitude of the coupling is the most important problem in condensed matter physics with important implications for multifunctional applications.1,5,6 Multiferroic magnetoelectric (ME) composites, i,e. composites of magnetostrictive and piezoelectric materials, are very important compared to single-phase magnetoelectric materials for their much higher magnetoelectric coefficients and much higher critical temperatures.7,8 The overall magnetoelectric properties can be engineered by choosing


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suitable materials for both ferroelectric and ferromagnetic phases. Ferroelectric materials with large polarization and piezoelectric coefficients, magnetic materials with high magnetostriction, high resistivity, TN above room temperature and large magnetization are chosen for composites to produce a strong ME coupling above room temperature.1,5,6,8 In ME composites, constituent phases may or may not have any ME effect, but the cross-coupling between the phases can produce a remarkably large ME effect.6,8,9 The ME effect in composite materials is known as a tensor-product property,7,8,9 and is usually the product of the magnetostrictive effect (magnetic/mechanical effect) in the magnetic phase and the

piezoelectric

effect

(mechanical/electrical

effect)

in

the

ferroelectric phase;

electrostriction can also play a role. In ME composites the ME effect is therefore an extrinsic effect.6,8 The spinel ferrites are often chosen as the magnetic candidates in multiferroic composites due to their good thermal, chemical, and structural stabilities. Ni and Co ferrites are important magnetic materials with Cu, Zn, and Cr substitutions in A-sites resulting in increase of the electrical resistivity and saturation magnetization.4,6,9 Several studies have been made to observe higher polarization and magnetization along with higher critical temperature (both ferroelectric and magnetic) above room temperature and to achieve higher effective magnetoelectric coupling for various composite systems.10,11,12,13,14,15 But the studies of both ferroelectric and magnetic transitions with clear evidence of intrinsic (bulk, rather than interfacial) magnetoelectric coupling along with the nature

of

such

ME

coupling

at

room

temperature

are

limited.

The Pb(Fe0.5Nb0.5)O3-Co0.65Zn0.35Fe2O4 (PFN-CZFO) composite system has been chosen for the present study to observe both ferroelectric and ferromagnetic phase transitions and possibly with strong ME coupling above room temperature. PFN is a well-known multiferroic material with Curie temperature (TC) between 379-385 K having high dielectric constant, low loss tangent and high piezoelectric constant.12,16,17 Recently Carpenter et al.



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have reported the existence of ferroelectric, ferromagnetic and ferroelastic properties in PFN with interesting ferroelectric and magnetic properties.17 Cobalt zinc ferrites are soft magnetic materials with high saturation magnetization, low coercivity, high resistivity, high magnetostriction coefficient and low dielectric losses.12,18 Co0.65Zn0.35Fe2O4 has been chosen for the present work because this composition possesses the highest combination of saturation magnetization and magnetostriction in the entire Co–Zn series.18,19 The aim of this work is as follows: first, to study the ferroelectric and magnetic phase transition; second, to investigate the existence of intrinsic magnetoelectric coupling; and finally, to determine the nature of such magnetoelectric coupling in PFN-CZFO composite. I. Experimental details The (1-x) Pb (Fe0.5Nb0.5)O3 – x Co0.65Zn0.35Fe2O4 (x=0.20) composite will be abbreviated throughout this manuscript as PC2. This composite was synthesized by a conventional solid state route. The detailed synthesis conditions of this composite are reported elsewhere.11 Raman scattering studies were performed using a Horiba Jobin Yvon T64000 over a wide temperature range (83 K–500 K). The 514.5 nm line of the Ar ion laser was used as the excitation source. Dielectric parameters, i.e., capacitance, dissipation factor, impedance, and phase angles, were measured from 300 to 650 K in a wide frequency range 100 Hz to 1 MHz using an impedance analyzer HP4294A with MMR Technologies K-20 programmable temperature controller. Magnetic properties of the samples were obtained using a Quantum Design MPMS-XL7 superconducting quantum interference device (SQUID) magnetometer. Ferroelectric P-E loops were measured using a Radiant RT 6000 HVS after poling the sample under a voltage of 1200 V for 12 hrs using DC Power supply (TREK, Inc., Model: 677A) at room temperature. The magneto-dielectric measurements were performed using a magnet with varying field of up to ±2 T with a HIOKI 3532-50 LCR Hi-tester at room temperature.


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RESULTS AND DISCUSSION: Elemental Analysis: XRD pattern of this composite is the superposition of both the crystallographic phases of PFN and CZFO, showing the formation of the composite. The detailed structural properties of this composite are reported elsewhere.11 For the conclusive evidence of presence of all elements and to check the surface morphology with elemental mapping of the sintered pellet of PC2, scanning electron microscopy (SEM) was carried out and is displayed in Fig. 1(a). The corresponding electronic image with EDX mapping for all the elements is shown in Fig. 1(a) (inset). From this micrograph it is observed that the grain growth process is almost completed during the sintering process. The grains and grain boundaries are well defined with uniform distribution of grains throughout the surface of the sample. Dense homogeneous microstructures were observed with a minimum number of holes or cracks. The micrograph revealed the polycrystalline nature of microstructures with grains of different shapes and size ranging between ∼ 3 – 6 µm, The atomic wt% of each element present in and elementary mapping images of Pb, Fe, Nb, Co, Zn and O are shown in the inset of the Fig. 1(a). The color images illustrate quantitative analyses of materials present in the system.20 To investigate further and confirm the existence of all individual elements, high-resolution Xray photoelectron spectroscopy (XPS) measurements were carried out on the surface of PC2 sample, and the corresponding spectra are shown in Fig. 1(b). Photoelectron characteristic peaks of Pb 4f7/2(137.5), Pb 4f5/2 (142.48), Fe 2p3/2(710.7), Fe 2p1/2(724.3), Nb 3d5/2(205.84), Nb 3d3/2(208.7), Co 2p3/2(784.52), Co 2p1/2(~800), Zn 2p3/2 (1021.45) and O 1s (529.85) were observed in the high-resolution XPS spectra of PC2. All binding energies were referenced to the C1s (284.6eV) peak. Hence presences of all elements in this composite are confirmed by XPS studies along with SEM studies.



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Ferroelectric properties: Electrical polarization (P) versus electric field (E) hysteresis loop measurements have been performed at room temperature with different dc electric fields in order to verify the presence of spontaneous polarization and existence of ferroelectric properties of the sample PC2. The P-E hysteresis loop is shown in Fig. 2(a). The ferroelectric measurements were carried out after poling the sintered pellet at 1200 V for 12 hours. It is clearly seen from the figure that the loop saturates above 1000 V. The coercive field and remanent polarization increase with increasing electric field. The coercive field, remanent polarization and saturation polarization are found to be 10.1 kV/cm, 9.85 µC/cm2, and 21.5µC/cm2 respectively at the highest electric field. The well-saturated hysteretic behavior implies the presence of ferroelectric properties. Dielectric and Calorimetric properties: Understanding the mechanisms of the phase transition and confirming it through various measurements is a central challenge in material science: Ferroelectrics are a classical set of materials characterized by the appearance of a spontaneous polarization (the order parameter) below the transition point separating paraelectric (high-symmetry) and ferroelectric (low symmetry) phases. The polarization direction can be switched between two (or more) orientation states; and it is essentially this property that many ferroelectric applications utilize. The order and nature of the phase transition dictate the number of orientation states available below the transition point. In order to get insight into the ferroelectric phase transition, the dielectric properties, especially dielectric constant (εr) and inverse of dielectric constant as a function of temperature (300-600K) have been studied, and measurements at a frequency of 50 kHz are shown in the upper portion of Fig. 2(b). It has been observed that εr increases gradually with increase in temperature to its maximum value (εmax) and then decreases. This observed dielectric anomaly signals the ferroelectric-paraelectric phase


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transition. In order to find out the exact ferroelectric-paraelectric phase transition temperature, we graphed the derivative of inverse of dielectric constant (not shown), and the phase transition temperature was found to be 428K. The presence of magnetic phase and the magnetoelectric coupling might be the reason of shifting of the Tc of the composite towards higher temperature (~ 428K). To further confirm this phase transition we have also carried out the differential scanning calorimetry (DSC) studies. The DSC measurements have been carried out from room temperature to 600 K as shown in lower portion of Fig. 2(b). The presence of an endothermic peak around 438 K in the heat flow curve corresponds to the ferroelectric-paraelectric phase transition (Tc). The endothermic peak temperature in DSC thermogram is nearly same as the ferroelectric phase transition temperature obtained from dielectric study for PC2 within the experimental uncertainty.21,22 Therefore we conclude that the anomaly observed in temperature-dependent dielectric spectroscopy is genuine, which is also further supported by Raman spectroscopic studies. Fig. 2(c-d) show the complex impedance spectra (Nyquist plot) of PC2 at different temperatures. A clear change in the pattern of the complex impedance spectra has been observed with increase in temperature. In the low-temperature region (below Tc), the beginning of formation of a semi-circular arc has been observed with rise in temperature; these semicircular arcs become distinct at higher temperatures. The appearance of a single semicircular arc at low temperature is due the bulk property of material. We found a close agreement between the experimental and the simulated data for all temperatures. Just above the phase transition, the impedance spectra are more skewed. This may be due to a distribution of relaxation times: the closer T is to the transition, the longer is the time taken by the relaxing dipoles. In the high-temperature range (above Tc), the impedance spectra are characterized by the appearance of two semicircular arcs with their centers lying below the real axis, the classic signature of the presence of a constant phase element (CPE). [Note



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however that CPE’s are empirical and do not in themselves identify their origin, which is thought to be defects]. The two circular arcs become resolved, and clearly two distinct semicircles are observed with increasing temperature. The high-frequency semicircle is due to the bulk (grain) property of the material, whereas the low-frequency semi-circular is due to the grain boundary properties of the material. The low- and high-frequency semicircular arcs of the impedance spectra can be modeled by an equivalent circuit of: (i) a resistance (bulk resistance), capacitance (bulk capacitance) and a CPE connected in parallel; (ii) a parallel combination of a resistance (grain boundary resistance) and a CPE, with all these connected in series. We have fitted the temperature dependent Nyquist plot using this equivalent circuit, as shown in the inset of Fig. 2(c,d) and found that a close agreement between the experimental and the simulated data for all temperatures. The justification of proposed equivalent circuit is reported elsewhere.23,24 The intercept of the semicircular arcs on the real axis give the bulk and grain boundary resistance of the material. It has been found that both the grain and grain boundary resistance decrease with rise in temperature. It suggests that with increase in temperature the bulk and grain boundary conductivity increase, which is behavior typical of semiconductors.25,26 Polycrystalline ceramics are usually made up of grains with each grain consisting of either single or multiple micro-domains. Above the phase transition temperature there is nucleation of domain walls near defects at the grain boundary. Changes of the position of different cations also lead to changes in the electrical properties/polarization of the grain. So the spontaneous polarization closely related to the motion of dipoles/cations leads to the potential barrier in the ferroelectric system. This mechanism may be responsible for changes in the pattern of impedance spectra below and above phase transition temperature. It is well known that the spontaneous polarization generally decreases with increase in temperature and disappears above the transition temperature. Whenever there is a transition from ferroelectric to paraelectric phase, there is a


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decrease in the barrier height. This leads to a decrease in the activation energy, which results in decrease of the both grain and grain boundary resistance.27 Temperature-Dependent Raman Studies: Raman scattering is a nondestructive tool to study the complex structure of strongly correlated electron systems such as multiferroic materials, with compositional and structural disorder; it is highly sensitive to local symmetry change. It is also useful in estimating the ferroelectric transition temperature associated with structural phase transitions. Fig. 3 (a) shows the temperature-dependent Raman spectra of PC2. In the present studies the assignments of phonon branches for PC2 were based on the published reports for PFN and CZFO. 8,28 The peak positions of various Raman modes associated with PFN have been found at 64, 138, 215, 265, 427, 488, 590, 697, 791, 861, 971, 1123, and 1236 cm-1. The appearance of excess Raman peaks in PFN over the predicted four modes for a cubic perovskite (i,e 2F2g+Eg+A1g) could be due to octahedral tilting and/or polar distortions leading to local symmetry-breaking. There are five first-order Raman active modes (A1g +Eg +3T2g) expected in CZFO at ambient conditions.26 In our CZFO compound the peaks occur around 304, 468 and 615, 690 cm-1, whereas the most intense peaks are found at 468 and 690 cm-1. The Raman spectra of PC2 show all the peaks corresponding to separate PFN and CZFO materials, which confirms the formation of the composite. The peaks at 205 and 785 cm-1 are ascribed to the Nb-O stretching mode; and the peak at 695 cm-1 is ascribed to the Fe-O stretching mode. The most intense peak of CZFO (~468 cm-1) is not clearly visible in the composite, probably because there is only 20 % of CZFO present in the composite, and the 690 cm-1 peak merged with the peak of pure PFN. Moreover, all these peaks are slightly redshifted from their positions compared to the end-member compounds, which may be due to the introduction of disorder or stress developed in this composite.



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In order to understand the phonon dynamics and to get a clear picture of the ferroelectric phase transition which was confirmed independently by both temperature dependent dielectric spectra and thermal (DSC) measurements, temperature dependent Raman studies were carried out in the temperature range of 83-500 K. From the temperature dependent dielectric spectra the ferroelectric transition is found to be ~ 428 K which is supported by DSC thermograms. The peak positions and FWHM of these phonon modes at different temperature were analyzed by fitting the Raman spectra with a damped harmonic oscillator model which can be written as =

Where n = (e hω / kT − 1)

---------------------------------------------------------------(1)

is the phonon occupation number, ω0 , Γ0 and χ 0 are the peak

position, the line width and peak intensity respectively. The Fitted Raman spectrum at 83 K is shown in Fig. 3(b). The computed mode frequencies and FWHM of different phonons versus temperatures are shown in Fig. 3(c) and 3(d) respectively. The following changes were observed in the spectra with increasing temperature: (i) peak intensities diminish; (ii) most of the intense peaks shift towards lower wave-numbers; and (iii) most of the peaks broaden and merge into a broad peak and disappear completely as the temperature approaches (Tc). These observations can be described by thermal broadening and thermal disorder, anharmonic lattice effects. Besides these effects, the change in bond length between oxygen and other cations (thermal expansion) will decrease vibrational frequencies with increasing temperature. All peaks show change in their lineshapes, but for clarity we show only the mode frequencies and FWHM of peaks with high intensities: Those at 216 and 788 cm−1 are plotted against temperature in Fig. 3(c) and 3(d), revealing a few perceptible spectral changes in the vicinity of the ferroelectric transition temperature. Smith et al. reported that such changes are an indication of phase transitions.29 Similarly Hoshina et al. also reported similar


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observations in BaTiO3 to infer a ferroelectric phase transition.30 In another study Dobal et al. demonstrated the loss of intensity of some phonon modes with increase of temperature and disappearance of those modes around the ferroectric-paraelectric phase transition temperature in BaZrxTi1-xO3.31 Tavares et al. also reported a complete disappearance of the Raman spectra above the transition temperature in Pb0.95La0.05TiO3 films prepared by the mixed oxide method.29 Our observations are thus typical and consistent with prior literature.30 In our case the mode at 216 cm−1 shifts significantly towards lower frequency with increasing temperature and disappears above Tc. Another mode at 788 cm−1 shifts slightly towards lower wave-number and also disappears around Tc. For both modes the FWHM increases gradually with temperature until the peak vanishes around Tc, implying an orderdisorder transition. The absences of the Raman modes at above certain temperature indicates either the material has decomposed and become amorphous or with all atoms are at center of inversion or it has undergone a structural phase transition to its cubic phase. We examined the possibility of the former case by recording the Raman spectra of the sample by cooling it down to room temperature. We noticed all the peaks distinctly reappear at room temperature, which rules out the possibility of complete decomposition of the sample and establishes the fact that the sample indeed transformed to a cubic phase above Tc. Hence the ferroelectric phase transition is confirmed by Raman spectroscopic studies.

Magnetic Properties and Phase Transition: Figure 4 (a, b) show zero-field-cooled/field-cooled (ZFC-FC) behavior from 2-395 K at 100 Oe and temperature-dependent magnetic hysteresis loops of PFN-CZFO composite respectively. In our sample, the well-known antiferromagnetic Neel temperature peak occurs around 152 K, whereas in the low- temperature regime (152 K) a ferromagnetic order, and a paramagnetic (PM) relaxor phase (>270 K) above that. The magneto-dielectric measurements provide direct evidence of magneto-electric coupling via strain at room temperature. Room temperature magnetic control of electrical ordering confirms the existence of ME coupling (bulk but nonlinear ME coupling) in this composite. The change of bulk capacitance with magnetic field implies the existence of intrinsic magneto-electric coupling. These results show that this composite shows strong magnetoelectric coupling of biquadratic nature at room temperature, which can be useful for potential multifunctional device applications.

Acknowledgments: This work was supported by DOE Grant No. # FG02-08ER46526. Dhiren K. Pradhan and Shalini Kumari acknowledge IFN (NSF Grant # EPS - 01002410) for fellowship. We are very much thankful to Prof. R. Palai of University of Puerto Rico for providing magneto-dielectric measurement facilities and Dr. C. V. Rao for FESEM measurements.

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2013,113, 074105.



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(21) Kumari, S.; Ortega, N.; Kumar, A.; Pavunny, S. P.; Hubbard, J. W.; Rinaldi, C.; Srinivasan, G.; Scott, J. F.; Katiyar, R. S. Dielectric Anomalies Due to Grain Boundary Conduction in Chemically Substituted BiFeO3. J. Appl. Phys. 2015, 117, 114102. (22) Tripathy, S. N.; Pradhan, D. K.; Mishra, K. K.; Sen, S.; Palai, R.; Paulch, M.; Scott, J. F.; Katiyar, R. S.; Pradhan, D. K. Phase Transition and Enhanced Magneto-dielectric Response in BiFeO3-DyMnO3 Multiferroics. J. Appl. Phys. 2015, 117, 144103. (23) Pradhan, D. K.; Choudhary, R. N. P.; Rinaldi, C.; Katiyar, R. S. Effect of Mn Substitution on Electrical and Magnetic Properties of Bi0.9La0.1FeO3. J. Appl. Phys. 2009, 106, 024102. (24) Pradhan, D. K.; Misra, P. Puli, V. S.; Sahoo, S. Pradhan, D. K.; Katiyar, R. S. Studies on Structural, Dielectric, and Transport Properties of Ni0.65Zn0.35Fe2O4. J. Appl. Phys. 2014, 115, 243904. (25) West, A. R.; Sinclair, D. C.; Hirose, N. Characterization of Electrical Materials, Especially Ferroelectrics, by Impedance Spectroscopy. J. Electroceram. 1997, 1, 65-71. (26) Macdonald, J. R. Note on the Parameterization of the Constant-phase Admittance Element. Solid State Ion. 1984, 13, 147-149. (27) Park, J. H.; Choi, B. C. Impedance Spectroscopy of (Pb0.98La0.02)(Zr0.95Ti0.05)O3(PLZT2/95/5) Ceramics Above Ferroelectric Phase Transition Temperatures. Journal of Crystal Growth, 2005, 276, 465-470. (28) Yaseneva, P.; Bowker, M.; Hutchings, G. Structural and Magnetic Properties of ZnSubstituted Cobalt Ferrites Prepared by Co-precipitation Method. Phys. Chem. Chem. Phys.,

2011, 13, 18609-18614. (29) McCauley, D.; Newnham, R. E.; Randall, C. A. Intrinsic Size Effects in a Barium Titanate Glass-Ceramic. J. Am. Ceram. Soc. 1998, 81, 979-987.


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(30) Hoshina, T.; Kakemoto, H.; Tsurumi, T.; Wada, S. Size and Temperature Induced Phase Transition Behaviors of Barium Titanate Nanoparticles. J. Appl. Phys. 2006, 99, 054311. (31) Dobal, P. S.; Katiyar, R. S. Studies on Ferroelectric Perovskites and Bi-layered Compounds Using Micro-Raman Spectroscopy. J. Raman Spectrosc. 2002, 33, 405-423. (32) Binder, K.; Young, A.P. Spin glasses: Experimental Facts, Theoretical Concepts, and Open Questions. Rev. Mod. Phys. 1986, 58, 801-976. (33) Kleemann, W.; Binek, C. Magnetic Nanostructures. Springer 2013, 246, 163. (34) Falqui, A.; Lampis, N.; Geddo-Lehmann, A.; Pinna, G. Low-Temperature Magnetic Behavior of Perovskite Compounds PbFe1/2Ta1/2O3 and PbFe1/2Nb1/2O3. J. Phys. Chem. B

2005, 109, 22967-22970. (35) Cheng, Z. X.; Wang, X. L.; Alvarez, G.; Dou, S. X.; Zhang, S. J.; Shrout, T. R. Magnetic Glassy Behavior in Ferroelectric Relaxor Type Solid Solutions: Magnetoelectric Relaxor. J. Appl. Phys. 2009, 105, 07D902. (36) Schmidt, R. ; Ventura, J. ; Langenberg, E. ; Nemes N. M. ; Munuera, C. ; Varela, M. ; Hernandez, M. ; Leon, C.; Santamaria, J. Magnetoimpedance Spectroscopy of Epitaxial Multiferroic Thin Films. Phys. Rev. B 2012, 86, 035113. (37) Dutta, D. P.; Mandal, B. P. ; Naik, R.; Lawes, G.; Tyagi, A. K. Magnetic, Ferroelectric, and

Magnetocapacitive

Properties

of

Sonochemically

Synthesized

Sc-Doped

BiFeO3 Nanoparticles. J. Phys. Chem. C 2013, 117, 2382- 2389. (38) Katsufuji, T.; Takagi, H. Coupling Between Magnetism and Dielectric Properties in Quantum Paraelectric EuTiO3 Phys. Rev. B 2001, 64, 054415. (39) Katsufuji, T.; Takagi, H. Magnetocapacitance and Spin Fluctuations in the Geometrically Frustrated Magnets R2Ti2O7 (R=rare earth). Phys. Rev. B 2004, 69, 064422.



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(40) Evans, D. M.; Alexe, M.; Schilling, A.; Kumar, A.; Sanchez D.; Ortega, N.; Katiyar, R. S.; Scott, J. F.; Gregg, J. M. The Nature of Magnetoelectric Coupling in Pb(Zr,Ti)O3– Pb(Fe,Ta)O3. Adv. Mater. 2015, 27, 6068–6073. (41) Daraktchiev, M.; Catalan, G.; Scott, J. F. Landau Theory of Domain Wall Magnetoelectricity. Phys. Rev. B 2010, 81, 224118.

Figure Captions: Fig. 1(a). (Color online) Scanning electron micrograph of PC2 composite at room temperature.

Fig. 1(b). (Color online) XPS spectra of all elements in PC2 composite at room temperature. Fig. 2(a). (Color online) Ferroelectric (P-E) hysteresis loops of PC2 at room temperature. Fig. 2(b). (Color online) Temperature dependence of dielectric constant (left panel), reciprocal of permittivity (right panel), and DSC thermogram (lower panel) of PC2.

Fig. 2(c). (Color online) Complex impedance plot (symbol), fitted data (solid line), and equivalent circuit before phase transition (300-420 K.)

Fig. 2(d). (Color online) Complex impedance plot (symbol), fitted data (solid line), and equivalent circuit after phase transition.

Fig. 3(a). (Color online) Temperature dependence of Raman spectra of PC2 composite at all temperatures.

Fig. 3(b). (Color online) Fitted Raman spectra at 83 K with Lorentzian function using Peakfit program.

Fig. 3(c). (Color online) Temperature dependence of peak positions of peak 216 and 788 cm1

of PC2 composite.

Fig. 3(d). (Color online) Temperature dependence of FWHM of peak 216 and 788 cm-1 of PC2 composite.


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Page 23 of 37


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Fig. 4(a). (Color online) Temperature dependence of magnetization for PC2 measured with zero field cooling (ZFC) and field cooling (FC) with applied field of 100 Oe.

Fig. 4(b). (Color online) M-H hysteresis loops of PC2 composite at different temperature, enlarged M-H loops and temperature dependence of Hc and Mr (in inset).

Fig. 5. (a) (Color online) M-H loops of PC2 before and after electrical poling. Fig. 5(b). (Color online) Frequency dependence of capacitance of PC2 at different magnetic field.

Fig. 5(c). (Color online) Complex impedance plot (symbol), fitted data (solid line), and equivalent circuit at different magnetic field.

Fig. 5(d). Magnetic field dependence of bulk capacitance (left panel) and bulk resistance (right panel) of PC2 composite.

Fig. 6. (Color online) Variation of (a) dM/dH (b) -M(dM/dH) and (c) dC-1/dH as a function of magnetic field.



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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment

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2400

0.0010

(b)

(a)

20

@ 50 kHz

V 500

-10 -20 -40

3000

ε 1600

-20 0 20 Electric Field (kV/cm)

(c)

0.0006

1200

Heat Flow (mW)

0

1/ r

10

0.0008

εr

4000

2

Polarization (µ C/cm )

2000

40

0.0004

-2.4

-2.6

-2.8

300

350

120

Rb

400 450 500 Temperature (K)

Rb

550

600

(d)

R gb

CPE

CPE

CPE

Cb

2000

80

Cb

-Z" (kΩ)

1000

460 K

Fitted

T

T

-200

200

400 600 Z' (kΩ)

800

2

620 K 650 K Fitted

0

0

0

Rgb

CPE

1

Before Phase Transition 420 K

Rb

CPE

3

40

300 K

0

After Phase Transition Fitted

-Z" (kΩ)

-Z" (kΩ)

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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

0

580 K

1000

4

8

12

Z' (kΩ)

0

Figure 2. Pradhan et al.


40

Z' (kΩ)

80

120


Page 26 of 37

26

(a)

200

(b)

400 600 800 1000 Ramam Shift (cm-1)

Intensity (a.u)

428 K 413 K 398 K 373 K 348 K 323 K 308 K 283 K 258 K 233 K 208 K 183 K 158 K 133 K 108 K 83 K

Intensity (a.u)

0

200

1200

(c)

788

300 400 600 -1 Raman shift (cm )

800

(d)

90 788 cm-1 60

788 cm-1

784

FWHM

Raman shift (cm-1)

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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

220

216 cm-1

30 150

216 cm-1

100

210

50

200

0 100

200 300 Temperature (K)

400

100




400

Page 27 of 37


FC ZFC

Magnetization (emu/g)

20

(a)

270 K

16

@100 Oe 12

8 0


300

10

400

(b)

30

10K

15

M (emu/g)

10K

T

T

0 -5

320K

-10 -1.0

-0.5

0

0.0 H (kOe)

0.5

1.0

900 12

Mr (emu/g)


5

-15

600

Hc (Oe)

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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

8

300 4 0 0

-30

0

-20

100

T(K)

-10 0 10 Magnetic Field (kOe)



200

300

20


Page 28 of 37

28

1.0

-10

(a)

0.0

-0.5

-1.0 -0.2

-0.1

0

0.0 H (kOe)

0.1

0.2

-8

Before Poled

-10

6.0x10

-3.0 -2

-10

5.7x10

3000

10

2

15

0T 0.5 T 1T 2T Fitted

0 0

25

50

Z" (kΩ )

1000

H

10

4

10 Frequency (Hz)

5

10

(d)

Rb(MΩ )

Cb

2

6

10

120

CPE

2000

2400

3

10

(c)

Rb

-1 0 1 Magnetic Field (T)

0T + 0.5 T +1T +2T

-10


-1.5

-2.5 -10

5.8x10

5.5x10

-10

@1kHz

-1.0

-2.0

-10

-16

Z" (kΩ)

-10

5.9x10

5.6x10

After Poled

-15

0.0 -0.5

MC(%)

8

After Poled

Capacitance (F)

M(emu/g)


0.5

(b)

6.1x10

Before Poled

16

550.0p

110 545.0p

Cb(F)

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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

100

2300

540.0p

2200 2100

90

2000 95

100

105

110

115

120

Z' (kΩ)

75

100

Z' (kΩ)

125

150

0.0

0.5

1.0

1.5

2.0

Magnetic Field (T)



535.0p 2.5

Page 29 of 37


0.04 (a)

dM/dH

0.03

0.02

0.01

0.00 -20

-10

0 10 Magnetic Field (kOe)

20

0.10

-M(H)*dM/dH

(b)

0.05

0.00

-0.05

-0.10 -20

-10


20

4

4.0x10

(c)

@ 100 kHz 4

d(C-1)/dH (a. u.)

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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2.0x10

0.0

4

-2.0x10

4

-4.0x10

-20

-10 0 Magnetic Field (kOe)

10

20




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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

TOC Graphic


Page 30 of 37

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(a)

Pb

Pb

(b)

Nb

Fe

Co

Zn

137.5 4f7/2

142.48 4f5/2

O

724.3 2p1/2

Fe Sat

710.7 2p3/2 Sat

13.6

4.9

148 146 144 142 140 138 136

740

730

205.84 3d5/2

Nb

Intensity(a.u)

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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


720

710 784.52 2p3/2

Co

208.7 3d3/2

~ 800 2p1/2

2.8 212

210

208

206

204

810

1021.45 2p 3/2

Zn

1024

15.5

1022

1020

800

534

532

Binding Energy (eV) Figure 1. Pradhan et al.


780

529.85 1s

O

1018

790

530

528

526


2400

 1600

V 500

-10 -20 -40

-20 0 20 Electric Field (kV/cm)

(c)

0.0006

1200 0.0004

Heat Flow (mW)

0

1/ r

10

0.0008

r

2

Polarization (C/cm )

@ 50 kHz

2000

4000

3000

0.0010

(b)

(a)

20

40

-2.4

-2.6

-2.8

300

120

Rb

350

400 450 500 Temperature (K)

Rb

(d)

550

600

Rgb

CPE CPE

CPE Cb

80

2000

Cb

-Z" (k)

1000

After Phase Transition Fitted 40 460 K

300 K

Fitted

T

0

T

Before Phase Transition 420 K

-200

200

400

600 Z' (k)

800

1000

Rgb

CPE

2

1

620 K 650 K Fitted

0

0

0

Rb

CPE

3 -Z" (k)

-Z" (k)

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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 37

0

580 K

4

8

12

Z' (k)

0



40

Z' (k)

80

120

Page 33 of 37

(a)

200

(b)

400 600 800 1000 Ramam Shift (cm-1)

Intensity (a.u)

428 K 413 K 398 K 373 K 348 K 323 K 308 K 283 K 258 K 233 K 208 K 183 K 158 K 133 K 108 K 83 K

Intensity (a.u)

0

200

1200

300 400

600

800 -1

Raman shift (cm ) (c)

788

(d)

90 788

cm-1

60 788 cm-1

784

FWHM

Raman shift (cm -1)

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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


220

216 cm-1

30 150

216 cm-1

100

210

50

200

0 100


400

100




400


FC ZFC


20

(a)

270 K

16

@100 Oe 12

8 0


300

10

30

400

(b)

10K

15

M (emu/g)

10K

T

T

0 -5

320K

-10 -1.0

-0.5

0

0.0 H (kOe)

0.5

1.0

900 12

Mr (emu/g)


5

-15

600

Hc (Oe)

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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 37

8

300 4 0 0

-30

0

-20

100

T(K)




200

300

20

Page 35 of 37

1.0

-10

-0.5

(a)

0.0

-0.5

-1.0 -0.2

-0.1

0.0 H (kOe)

0

0.1

0.2

-8

Before Poled

-10

6.0x10

-10

5.9x10

-2.5 -3.0 -2 -10

5.7x10

-10

-10

3000


10

15

10

Rb(M)

Cb

0T 0.5 T 1T 2T Fitted

0 0

25

50

Z" (k)

2400

1000

H

2

10

3

4

10 Frequency (Hz)

10

5

(d)

CPE

2000

2

10

6

120

(c)

Rb


0T + 0.5 T +1T +2T

5.5x10

-15

-1.5

-10

5.8x10

-10

After Poled

@1kHz

-1.0

-2.0

5.6x10

-16

Z" (k)

MC(%)

After Poled

Capacitance (F)

8

0.0

(b)

6.1x10

Before Poled

0.5

M(emu/g)


16

550.0p

110 545.0p

Cb(F)

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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100

2300

540.0p

2200

2100

90

2000 95

75

100

Z' (k)

105

110

Z' (k)

100

115

125

120

150

0.0

0.5

1.0

1.5

2.0

Magnetic Field (T)



535.0p 2.5


0.04 (a)

dM/dH

0.03

0.02

0.01

0.00 -20

-10


20

0.10 (b)

-M(H)*dM/dH

0.05

0.00

-0.05

-0.10 -20 4.0x10

-10


2.0x10

20

4

(c)

@ 100 kHz d(C-1)/dH (a. u.)

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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 37

4

0.0

-2.0x10

4

-4.0x10

4

-20

-10 0 Magnetic Field (kOe)



10

20

Page 37 of 37

TOC Graphic

0.0

-10

6.1x10

MC(%)

-0.5 -10

6.0x10

Capacitance (F)

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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Pb

Fe

Nb

Co

Zn

O

-10

5.9x10

@1kHz

-1.0 -1.5 -2.0 -2.5

-10

5.8x10

-3.0 -2

-10

5.7x10


2

0T + 0.5 T +1T +2T

-10

5.6x10

-10

5.5x10

10

2

10

3

4

10 Frequency (Hz)


10

5

10

6

Studies of Phase Transitions and Magnetoelectric Coupling in PFN

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