Synthesis and characterization of multiferroic composites

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SYNTHESIS AND CHARACTERIZATION OF MULTIFERROIC COMPOSITES

ARTI GUPTA

DEPARTMENT OF PHYSICS

INDIAN INSTITUTE OF TECHNOLOGY DELHI

DECEMBER 2010

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SYNTHEIS AND CHRACTERIZATION OF MULTIFERROIC COMPOSITES

by

ARTI GUPTA Department of Physics

Submitted

In fulfillment of the requirement of the degree of Doctor of Philosophy

to the

Indian Institute of Technology Delhi

December 2010

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CERTIFICATE

This is to certify that the thesis entitled "Synthesis and Characterization of Multiferroic Composite" being submitted by Ms. Arti Gupta, has been done under my supervision in conformity with the rules and regulation of the Indian Institute of Technology Delhi. I further certify that the thesis has attained a standard required for the award of degree of Doctor of Philosophy of the institute. This work or any part of this work has not been submitted elsewhere for the award of any other degree or diploma.

Supervisor

Prof. Ratnamala Chatterjee Department of Physics Indian Institute of Technology Delhi

New Delhi-110016, India

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ACKNOWLEDGEMENT

I want to express a great deal of gratitude and respect to my supervisor Prof. Ratnamala Chatterjee, Indian Institute of Technology, Delhi. Her constant support, guidance and encouragement greatly helped me throughout my PhD programme. Her constructive criticism and valuable suggestions has made the best presentation of the work done in this thesis.

I greatly thank Council of Scientific & Industrial Research (CSIR) India for providing fellowship. I would like to thank Prof. B. K. Chougale, Shivaji University, Kolahpur for elaborating the useful insights of my research work. I would like to thank Dr. P. A. Joy at NCL (India) for magnetostriction measurements. I would like to thank Dr. 0. P. Thakur and Dr. Sanjay Pandey at SSPL (India) for helping me in the experimental work. I am thankful to Dr. D. Kanjilal at NSC (India) for giving important discussion on ion beam implantation and irradiation process. I would also like to thank Dr. S. R. Shannigrahi at Institute of Material Research & Engineering (IMRI), Singapore for helping me in the experimental work.

I would also thank my lab members for helping me during research work. I also thank the technical staff at Indian Institute of Technology Delhi for providing various experimental facilities. I would like to thank Mr. Narendra Kumar for his help in my experimental work.

Finally I greatly thank my family members for their constant moral support and encouragement throughout this long period of PhD programme.

Place: New Delhi

Date-20-12-2010 Arti Gupta

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Abstract

The multiferroic materials are those that combine two or all three so-called ferroic properties such as ferroelectricity, ferromagnetism, ferroelasticity. Recently a great attention has been paid to the magnetoelectric multiferroic materials that simultaneously exhibit both ferroelectric and ferromagnetic properties along with a magnetoelectric (ME) coupling. Observation of ME coupling in a material implies that the electric polarization/magnetization in this material can be induced on application of magnetic/electric field; these are defined as direct and converse ME effect respectively.

Such materials exhibit more than one functionality that could lead to entirely new device concept like electric field controlled magnetic data storage. With this type of random access memory (RAM), data could be read magnetically and written electrically which would be faster and less power consuming. These multiferroic materials can be classified in two categories (i) single phase compounds or solid-solutions and (ii) bi-phase composites. The natural single phase compounds are rare, in addition their ME coupling is too weak and thus have limited use for practical applications. These compounds were further modified by the substitution of various ions to prepare single-phase solid solutions that improved ME effect to some extent. Technologically, composite multiferroic materials are of greater interest and it is also the topic of this present thesis.

There are several advantages of composite materials over single phase solid solutions as ME coupled magnetoelectric multiferroics. In 1972, Van Suchtelene introduced the concept of bi-phase composites consisting of magnetostrictive and piezoelectric phases to overcome the drawbacks associated with single phase materials.

In these composites, ME effect appears as a product property although the individual

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component phases do not exhibit any ME effect. In this way the composite multiferroics offer higher design flexibility using multiple choices of components from well known magnetostrictive and piezoelectric phases. In these composites, ME effect results from the strain mediated mechanical coupling between the two phases. On application of magnetic field, the magnetic particles change their shape due to magnetostriction and the strain thus produced passes on to the piezoelectric phase, applies stress over it resulting in to induction of voltage due to piezoelectric effect.

Thus, the magnetoelectric voltage coefficient ^(aE) is a measure of the performance of ME material for required application and is measured in terms of voltage induced on application of magnetic field i.e.

dE

aE

dH

=

a E

=( dE ), Id

aE

— (dE

JdT), (dH dT dx

dx

aE

=

g33C33

•

_dH

where

(dx/dH) is

the piezomagnetic coefficient of the magnetostrictive phase, generally written in the literature of magnetic materials as

(d.t/dH), T

is the stress, g33 is the piezoelectric voltage coefficient and C33 is the stiffness coefficient of the piezoelectric phase. Clearly, for high ME voltage coefficient in composite, a suitable combination of piezoelectric (with high piezoelectric voltage coefficient) and magnetostrictive (with large piezomagnetic coefficient, high A) components synthesized in optimized conditions with homogenous microstructure is required. The ME voltage coefficient of the composites also depends on the mole ratio of the two component phases, their

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connectivity pattern, the method and conditions of fabrication etc. Thus, in recent years there is a surge in research efforts to design composite magnetoelectric multiferroic materials with large ME voltage coefficient, by making appropriate choices as mentioned above.

In the present thesis we have explored some of the above mentioned approaches to demonstrate (i) improved flexible composite using novel connectivity pattern in fabrication of BaTiO3-CoFe2O4-PVDF (BT-CFO-PVDF) with an order of magnitude increased value of magnetoelectric voltage coefficient (aE - 26 mV/cm.Oe), (ii) new, improved magnetostrictive component with appreciably high A, and d)JdH, achieved by appropriate chemical substitution, is introduced, resulting in enlarged magnetoelectric voltage coefficient (aE - 87-122 mV/cm.Oe) in PZT-(Co,Zn)(Fe,Mn)204 and (iii) ME effect in Fe-BaTiO3 multilayer system, prepared using low energy ion implantation technique. All these experimental work/demonstrations were based on theoretical predictions/ calculations that appeared in literature during the period (2001-2006), as described below in some detail.

The thesis is organized in eight chapters.

First chapter (Introduction) would give a brief introduction about the multiferroic materials, the need and advantages of the composite materials, basic introduction of piezoelectric and magntostrictive effect, literature survey of the development of such composite materials and their proposed future applications. Finally the orientation of the problem will be discussed.

Second chapter (Experimental Procedures & Characterization Techniques) would discuss the experimental methods used for preparing various types of composites.

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Brief introduction of the used characterization techniques for (1) Structural &

Microstructural Characterization (2) Electrical Properties (3) Magnetic properties (4) Magnetoelectric Properties are described. The home made magnetoelectric coefficient (static & dynamic) measurement system set up by the author is also discussed in this chapter.

Third to seventh chapters are the Results & Discussions of the problems addressed in this thesis

In Chapter 3, we describe the improved mechanical interaction in BT-CFO- PVDF composite multiferroics. The flexible matrix of PVDF results in large displacement transfer between the two component phases (BT and CFO) and as predicted by Nan et. al [117-119], such polymer matrix composite shows high magnetoelectric coupling.

A part of this work is published - Arti Gupta and Ratnamala Chatterjee, Journal of Applied Physics 106, 024110 (2009)).

The new CoFe2O4 based oxide (Coo.6Zno.4Fe1.7Mno.3O4) was used by the author as a magnetostrictive component in ME composite preparation with the standard piezoelectric PbZro.52Tio.48O3 at morphotropic phase boundary (MPB). The logic behind using [68, 71] the new Zn and Mn doped CFO is discussed in detail in chapter W.

Using this optimized ferrite composition Co0,6Zn0.4Fe1,7Mn0.3O4 (CZFMO) with high saturation magnetization (Ms- 78 emu/g) (close to pure CFO) and low coercivity (few Oe), introduced first time by the author of this thesis, two series of composite

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samples [x PbZro.52Tio.4803-(1-x) Coo.6Zno.4Fei.7Mno.304], with (i) x=0.65-0.80 and (ii) x=0.80-0.90 were prepared.

Chapter 4 discusses the results of ME properties of (x) PbZro.52TiO.4803- (1x) Co0,6ZnO.4Fe1,7MnO.3O4 composite series.

Results on x PbZrO.52TiO.48O3- (1-x) Co0.6Zn0.4Fe1.7Mn0.304 series where x= 0.65, 0.70, 0.75 and 0.8 are published as - Arti Gupta and Ratnamala Chatterjee, Journal of Magnetism and Magnetic Materials 322, 1020 (2010).

For x PbZrO.52Tio.48O3- (1-x) Co0.6Zn0.4Fe1.7Mn0.304 series where x=0.80, 0.85 and 0.90 (ferroelectric rich) dynamic ME effect was studied. The results are discussed in detail in Chapter 4. High ME voltage coefficient was obtained in the whole series;

the highest value— 122 mV/cm.Oe was obtained in x=0.90 at ac magnetic field of amplitude — 1 Oe and frequency — 1 kHz.

A part of this work is published, Arti Gupta, A. Huang, S. R. Shannigrahi and Ratnamala Chatterjee, Applied Physics Letters 98, 112901 (2011).

Chapter 5 describes the details of (x) BaTiO3-(1 x) Co0,6ZnO.4Fe1,7Mn0.304 composites where x=0.50, 0.60, 0.70 and 0.80). The dielectric anomaly for samples (x=0.70, 0.80) was observed close to the ferroelectric to paraelectric transition temperature of the BT whereas for samples (x=0.50, 0.60) it was found to be shifted towards higher temperatures. The highest value of ME coefficient (aE-73 mV/cm.Oe) at ac magnetic field of amplitude — 1 Oe and frequency — 1 kHz was observed in sample (x=0.50) containing equal molar ratio of two component phases.

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In 2006 Duan et. al [ 120] theoretically predicted and studied the ME effect in FeBaTiO3 multilayered system that originates from the interfacial bonding between Fe and BT layers.

In Chapter 6, we experimentally demonstrate this type of ME effect in Fe- BaTiO3 multilayer system prepared using low energy ion beam implantation of the Fe beam with fluence of 5x1016 ions/cm2, in BT single crystal and further annealed using swift heavy ion irradiation. The Fe-implanted BT crystal exhibited distinct change in magnetization close to the low temperature rhombohedral to orthogonal phase transition temperature of BT (T190 K), indicative of ME coupling in the sample.

A part of this work entitled "Manetoeletric effect in Fe embedded BaTiO3 single crystal caused by interfacial bonding" by Arti Gupta and Ratnamala Chatterjee is submitted for publication.

Chapter 7 would discuss the static ME behavior of the PZT-Ni04Zn0.6- 2 LiXFe2+XO4 bilayered composite (where x= 0.10, 0.15 and 0.20) in transversely magnetized and transversely polarized (TT) mode. In literature, Li substituted hot pressed nickel-zinc ferrite (Nio.4Zno.6-2XLiXFe2+XO4) is known to exhibit the improved magnetic properties (high saturation magnetization (Ms) & low coercivity (Hc)) hence, it was chosen as a magnetostrictive component. The magnetoelectric behavior of these samples was found to be in accordance of the reported magnetic behavior of Nio.4Zn0.6- 2XLiXFe2+XO4 [186, 187].

Chapter 8 (Conclusions and future scope) would give important conclusions of the thesis. In addition, it would also highlight the achievements and future scope in this field of research.

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List of Symbols

aE

: magnetoelectric voltage coefficient real part of dielectric constant

maximum value of dielectric constant eo : permittivity of free space

tan S : dielectric loss tangent T : temperature

H : magnetic field

Hac

: amplitude of ac magnetic field Tc' : ferroelectric Curie temperature

d : lattice spacing C : capacitance V : voltage F : frequency M : magnetization

Ms : saturation magnetization MR : remnant magnetization

He : coercivity

t : thickness of sample

real part of ac susceptibility imagery part of ac susceptibility

TBW : blocking temperature measured at given frequency

w : angular frequency

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zo : characteristic relaxation time K : effective magnetic anisotropy

VB

: particle volume A : area of electrode .1 :

wave length

d33 :

piezoelectric coefficient

X11 : longitudal

magnetostriction coefficient

?12

: transverse magnetostriction

coefficient qll : longitudal piezomagnetic coupling coefficient q12

:

transverse piezomagnetic coupling coefficient

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Abbreviations

BSEI : Back Scattered Electron Imaging

BT : Barium Titanate

CFO : Cobalt Ferrite

CZFMO : Manganese and Zinc Substituted Cobalt Ferrite EDXS : Energy Dispersive X-ray Spectroscopy

FC : Field Cooling

HRTEM : High Resolution Transmission Electron Micrograph

ME : Magnetoelectric

MPB : Morphotropic Phase Boundary

M-W : Maxwell-Wagner

PZT : Lead Zirconate Titanate PVDF : Polyvinylidene Di Fluoride

P(VDF-TrFE) : Polyvinylidene Fluride Tri Fluoroethylene RTA : Rapid Thermal Annealing

SAED : Selected Area Diffraction Pattern SEM : Scanning Electron Microscopy

SQUID : Superconducting Quantum Interference Device TEM : Transmission Electron Microscopy

XRD : X-Ray Diffraction ZFC : Zero Field Cooling

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LIST OF FIGURE CAPTION CHAPTER-I

Fig. No. Title of the figure Page No.

Fig.1.1 Ferroelectrics and ferromagnets form the subset of magnetically 4 (electrically) polarizable materials. The intersection with red

hatching represents the multiferroic materials. The blue hatching represents the magnetoelectrics, it is clear that the overlap between multiferroic and magnetoelectrics is incomplete.

Fig.1.2 Properties of composite materials (a) product property (b) 12 combination property (c) sum property.

Fig.1.3 Thin film nanostructured composite (a) 2-2 type superlattice 24 horizontal structure (b) 1-3 type vertical structure.

Fig.1.4 Typical ferroelectric hysteresis loop indicating the saturation 34 polarization (Ps), remanent polarization (PR) and coercivity (Ec).

Fig.1.5 Systematic representation of the perovskite unit cell. 35 Fig.1.6 Typical ferromagnetic hysteresis loop of ferromagnetic material. 37 Fig.1.7 Systematic illustration of magnetostriction phenomena. 38 Fig.1.8 Two neighboring octants of the unit cell of spinel ferrite 39

depicting the location of metal ions.

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CHAPTER-II

Fig. 2.1 Ion implantation set up with mass separator. 48 Fig.2.2 Schematic diagram of X-ray scattering to show Bragg's law. 52 Fig.2.3 Systematic diagram of Bragg Brentano Geometry. 53 Fig.2.4 Systematic diagram of scanning electron microscope. 55 Fig.2.5 Illustration of small amplitude measurement in SQUID (a) an

ideal SQUID response for a dipole and (b) the movement of the sample within the SQUID pick-up coils.

61

Fig.2.6 Photograph of magnetoelectric measurement set-up. 66

CHAPTER-III

Fig.3.1 X-ray diffraction pattern of pure BaTiO3 powder. 72 Fig.3.2 X-ray diffraction pattern of CoFe2O4 powder. 73 Fig.3.3 X-ray diffraction pattern of commercial PVDF. 73 Fig.3.4 (a) Dielectric constant (e') and (b) loss tangent (tan 6) vs.

temperature (T) plots at fixed frequencies for sample C-30.

77

Fig.3.5 (a) Dielectric constant (e') and (b) loss tangent (tan 6) vs.

temperature (T) plots at fixed frequencies for sample D-40.

77

Fig.3.6 (a) Dielectric constant (e') and (b) loss tangent (tan 6) vs.

temperature (T) plots at fixed frequencies for sample E-50.

78

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Fig.3.7 Variation of dielectric constant (e') and loss tangent (tan 6) vs. 78 frequency (f) for sample C-30.

Fig.3.8 Variation of dielectric constant (e') and loss tangent (tan 6) vs. 79 frequency (f) for sample D-40.

Fig.3.9 Variation of dielectric constant (e') and loss tangent (tan 6) vs. 79 frequency (f) for sample E-50.

Fig.3.10 Scanning electron micrograph of sample C-30. 80 Fig.3.11 Scanning electron micrograph of sample D-40. 81 Fig.3.12 Scanning electron micrograph of sample E-50. 81 Fig.3.13 Resistivity (p) vs. field (H) plot at room temperature for sample 83

C-30.

Fig.3.14 Resistivity (p) vs. field (H) plot at room temperature for sample 83 D-40.

Fig.3.15 Resistivity (p) vs. electric field (H) plot at room temperature for 84 sample E-50.

Fig.3.16 Magnetization (M) vs. field (H) plots at T=300 K for (a) sample 85 C-30 (b) sample D-40 and (c) sample E-50.

Fig.3.17 Plots indicating the coercivity (Hc), saturation magnetization 86 (Ms) and remnant magnetization (MR) of composite samples as

function of wt% of PVDF.

Fig.3.18 Magnetization (Al) vs. temperature (T) plots at constant field of 87 H=50 Oe in low temperature region for sample (a) C-30 (b) D-

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40 and (c) E-50.

Fig.3.19 Real

(x')

and imaginary

(x")

parts of ac susceptibility as 88 function of temperature (T) at fixed frequencies for sample C-30.

Fig.3.20 Real

(x')

and imaginary

(x")

parts of ac susceptibility as 89 function of temperature (T) at fixed frequencies for sample D-

40.

Fig.3.21 Real

(x')

and imaginary

(x")

parts of ac susceptibility as 89 function of temperature (T) at fixed frequencies for sample E-50.

Fig.3.22 Linear fitted £n(1 / 2,rv) vs. l / TBW plots for sample (a) C-30 (b) 90 D-40 and (c) E-50.

Fig.3.23 Magenetoelectric voltage coefficient (aE) vs. field (B) plots at 92 room temperature for (a) sample C-30 (b) sample D-40 (c)

sample E-50.

Fig.3.24 Maximum values of aE as a function of wt% of PVDF. 93 Fig.3.25 Capacitance (C) and loss tangent (tan 6) vs. field (H) plots for (a) 94

sample C-30 (b) sample D-40 (c) sample E-50.

Fig.3.26 Dielectric constant (e') and loss tangent (tan 6) vs. temperature 96 (T) plot at fixed frequencies along with magnetization (M) vs.

temperature (T) plot at constant field (HDc=50 Oe) for sample C- 30. A change in slope in the M-T graph can be clearly seen between T=360 K and T=380 K.

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CHAPTER-IV

Fig.4.1 X-ray diffraction patterns of composite samples (a) 80-20 (b) 75- 103 25 (c) 70-30 (d) 65-35.

Fig.4.2 Scanning electron micrographs for (a) 65:35, (b) 70:30, (c) 75:25 105 and (d) 80:20.

Fig.4.3 Variation of dielectric constant (e') and corresponding loss 107 tangent (tan 6) vs. temperature (7) (330 K<T<773 K) plots at

fixed frequencies (1 kHz<f<1 MHz) for all four samples.

Fig.4.4 (a) Dielectric constant (e') and (b) loss tangent (tan 6) vs. 108 frequency (f) plots at room temperature for all four samples.

Fig.4.5 Variation of magnetization (M) vs. temperature (T) at H=100 Oe 109 for all four samples.

Fig.4.6 Magnetization (M) vs. field (R) plots for sample 65:35 at T=300 110 K, T=430 K and T=530 K. Top inset shows inverse susceptibility

(1/X) vs. temperature (7) plot for sample 65:35 with 0=471 K and bottom inset shows enlarged (M-H) loop for sample 65:35 indicating it's low coercivity value.

Fig.4.7 Magnetization (M) vs. field (R) measurements at T=300 K for all 111 four samples.

Fig.4.8 Magnetoelectric voltage coefficient (aE) vs. field (R) plots at 112 room temperature for (a) sample 75:25 (b) sample 80:20.

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Fig.4.9 Enlarged view of loss tangent (tan 6) vs. temperature (T) plots 113 for all four samples atfi=100 kHz.

Fig.4.10 X-ray diffraction patterns for all three samples (80-20, 85-15 and 115 90-10).

Fig.4.11 X-ray diffraction patterns for (i) pure CZFMO (ii) pure PZT (R- 116 rhombohedral, T-tetragonal).

Fig.4.12 Back scattered images of all three composite samples. 117 Fig.4.13 Resistivity (p) vs. electric field (H) plots for all three samples at 119

room temperature.

Fig.4.14 Dielectric constant (e') and loss tangent (tan 6) vs. temperature 121 (7) (311 K<T<775 K) plots for all three samples in frequency

range (1 kHz<1 MHz).

Fig.4.15 Dielectric constant (e') and loss tangent (tan 6) vs. frequency (f) 122 plots for all three samples at room temperature.

Fig.4.16 Polarization (P) vs. electric field (H) loops for all three samples 123 at room temperature

Fig.4.17 (a) Magnetization (Al) vs. field (R) plots at T=300 K for all three 125 samples (b) Magnetization (Al) vs. field (R) plot for pure

sintered CZFMO at T=300 K. Inset of Fig.4.17 (b) shows the closed view of hysteresis loop for pure sintered CZFMO.

Fig.4.18 (a) Longitudinal magnetostriction coefficient ()l11) and (b) 127 Transverse magnetostriction coefficient (x,12) vs. field (R) plots

for CZFMO along with the respective piezomagnetic coupling

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coefficients (d),ll/dH and d),12/dI).

Fig.4.19 Magnetoelectric voltage coefficient (aE) vs. dc magnetic field 128 (H) plots for all three samples for a superimposed ac magnetic

field of amplitude— 1 Oe and frequency —1 kHz.

Fig.4.20 Piezoelectric coefficients (d33) for all three composite samples as 128 function of mole percentage of CZFMO.

Fig.4.21 Temperature derivative of magnetization (dM/dT) vs. 131 temperature (T) plots at constant field (H=50 Oe) for all three

samples. Inset of Fig. 4.20 shows magnetization (M) vs.

temperature (T) plots at H=50 Oe for all three samples.

Fig.4.22 Magnetization (M) and (dM/dT) vs. temperature (T) plot at H=50 132 Oe for pure CZFMO.

Fig.4.23 Magnetization (M) vs. field (H) loops at T=140 K and T=160 K 132 for pure CZFMO. Inset shows the enlarged view of M-H loops.

CHAPTER-V

Fig.5.1 X-ray diffraction patterns for all four samples. 134 Fig.5.2 Scanning electron micrographs of all four samples. 136 Fig.5.3 Dielectric constant (e') and loss tangent (tan 6) vs. frequency (f)

plots at room temperature for all samples.

138

Fig.5.4 Dielectric constant (e') and dielectric loss tangent (tan 6) vs.

temperature (T) plots at fixed frequencies for pure CZFMO.

139

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Fig.5.5 Dielectric constant (e') and dielectric loss tangent (tan 6) vs. 139 temperature (T) plots at fixed frequencies for pure BT.

Fig.5.6 Dielectric constant (e') and loss tangent (tan 6) vs. temperature 141 (T) plots for all four samples. Insets show the enlarged view of

plots in the temperature range (RT<T<300 °C).

Fig.5.7 Magnetization (M) vs. field (H) plots at T=300 K for all four 142 samples.

Fig.5.8 ME voltage coefficient (aE) vs. field (H) plots at room 144 temperature for samples 50-50 & 60-40. Insets show ME voltage

coefficient (aE) vs. field (H) plots for samples 70-30 and 80-20.

Fig.5.9 (dM/dT vs. T) plot for all four samples at H=50 Oe, red arrow 145 indicates the first anomaly related to CZFMO and blue arrow

indicates the second anomaly related to BT.

CHAPTER-VI

Fig.6.1 Dielectric constant (e') vs. temperature (T) plot for pristine BT 148 single crystal.

Fig.6.2 (a) HRTEM image indicating the lattice fringe pattern in 149 irradiated sample (b) SAED pattern taken on the irradiated

sample. Figs.6.2 (c) & (d) XEDS data taken on the different regions of crushed powder of irradiated sample.

Fig.6.3 (a) Magnetization (M1 ) vs. temperature (T) plots at (a) lower 153

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fields (H=20 Oe and 80 Oe) (b) higher fields (H=200 Oe, 500 Oe and 800 Oe).

Fig.6.4 Magnetization (M11) vs. temperature (T) plot at fields (H=20 Oe 154 and 80 Oe) for rapid thermal annealed sample.

Fig.6.5 Magnetization (Mi) vs. temperature (T) plots for the irradiated 155 sample. Inset shows the enlarged view of these plots close to the

(R-O) transition of BT.

Fig.6.6 Moment (m) vs. field (H) plot at T=6 K for irradiated sample. 156 Fig.6.7 M vs. H plots for the irradiated sample at T=170 K measured in 157

zero field cooled (ZFC) and field cooled (FC) conditions.

Fig.6.8 M vs. H plots for the irradiated sample at T=220 K measured in 157 zero field cooled (ZFC) and field cooled (FC) conditions.

CHAPTER-VII

Fig.7.1 Variation of magnetoelectric voltage coefficient (aE) vs. dc 162 magnetic field (H) for sample x0.10.

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SECTION-B

1.14 Basic features of ME composite 33

1.14.1 Ferroelectricity 33

1.14.2 Piezoelectricity 34

1.14.3 Perovskite oxides 35

1.14.4 Ferromagnetism 36

1.14.5 Magnetostriction 37

1.14.6 Spinel ferrites 38

Chapter II: Experimental Procedures & Characterization Techniques 40

2.1 Sample Preparation 40

2.1.1 Three phase (BaTiO3-CoFe2O4-PVDF) ceramic-polymer composite 40 2.1.1.1 Synthesis of BaTiO3 by conventional ceramic method 40 2.1.1.2 Synthesis of CoFe2O4 by co-precipitation method 42 2.1.1.3 Synthesis of three phase (BaTiO3-CoFe2O4-PVDF) composite

42 2.1.2 Two phase particulate sintered composite 43

2.1.2.1 Two phase [x PbZro.52Tio.4803-(1-x) Coo.6Zno.4Fe1.7Mno.304]

particulate composite where x=0.65, 0.70, 0.75 and 0.80 (low x series) 43 2.1.2.2 Two phase [(x) PbZro.52Tio.48O3-(1-X) Coo.6Zno.4Fe1.7Mno.304]

particulate composite where x=0.80, 0.85 and 0.90 (high x series) 44

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2.1.2.3 Two phase [x BaTiO3-(1-x) Coo.6Zno.4Fe1.7Mno.304] composite

where x=0.50, 0.60, 0.70 and 0.80 45

2.1.3 Two phase PbZro.52Tio.4803-Nio.4Zno.6-2XLiXFe2+XO4 bilayered composite

where x=0.10, 0.15 and 0.20 46

2.1.4 Fe-implanted BT single crystal 47

2.1.4.1 Low energy ion beam implantation 47

2.1.4.2 Swift heavy ion irradiation 48

2.1.4.3 Rapid thermal annealing. 49

2.1.4.4 Synthesis of ion-irradiated Fe implanted BaTiO3 single crystal 50

2.2 Characterization Techniques 51

2.2.1 Structural Properties 51

2.2.1.1 X-ray diffraction 52

2.2.1.2 Bragg Brentano Geometry 53

2.2.2 Electron Microscopy 54

2.2.2.1 Scanning electron microscopy (SEM) 54 2.2.2.2 Back Scattered Electron Imaging (BSEI) 55 2.2.2.3 Transmission electron microscopy (TEM) 56

2.2.3 Electrical Measurements 57

2.2.3.1 Polishing and electroding 57

2.2.3.2 Dielectric measurements 57

2.2.3.3 Ferroelectric measurements 58

2.2.3.4 Piezoelectric coefficient (d33) measurement 58

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2.2.4 Magnetic measurements 59

2.2.4.1 ZFC and FC curves 59

2.2.4.2 Superconducting quantum interference device (SQUID)

magnetometer 60

2.2.4.3 ac susceptibility measurements 62

2.2.5 Magntoelectric (ME) coupling measurements 63

2.2.5.1 Static method 64

2.2.5.2 Dynamic method 64

2.2.5.3 Magnetocapacitance measurement 66

Chapter III: Three-phase BaTiO3 - CoFe2O4-PVDF composite 68

3.1 X-ray diffraction pattern of component phases 71

3.2 Dielectric properties 74

3.3 Microstructural properties 79

3.4 Resistivity vs. field measurements 82

3.5 Magnetic properties 84

3.5.1 Magnetization (M) vs. field (H) measurements 84 3.5.2 Magnetization (M) vs. temperature (T) measurements 86

3.6 Magnetoelectric coupling measurements 91

3.6.1 Magnetoelectric voltage coefficient (aE) measurement 91

3.6.2 Magnetocapacitance measurement 93

3.6.3 Change in magnetic behavior around dielectric anomaly 95

3.7 Conclusions 97

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Chapter IV: Two phase PbZr0

.52

TiO

.48

03

-

Co0

,6

Zn0

.4

Fe1

,7

Mn0

_.3

04 composite 98

4.1 x PbZro,52Tio,4803-(1-x) Co0,6Zn0,4Fe1,7Mno,304 with x=0.65, 0.70, 0.75 and 0.80 (low

x series) 100

4.1.1 Structural Characterization of low x series 102

4.1.1.1 X-ray diffraction pattern 102

4.1.1.2 Scanning electron micrograph 104

4.1.2 Dielectric measurements of low x series 105

4.1.3 Magnetic measurements of low x series 108

4.1.3.1 Magnetization (M) vs. temperature (T) measurements 108 4.1.3.2 Magnetization (Al) vs. field (R) measurements 110 4.1.4 Magnetoelectric measurement of low x series 111

4.1.5 Conclusion 113

4.2 x PbZro,52Tio,4803-(1-x) Co0,6Zn0,4Fe1,7Mn0,304 with x=0.80, 0.85 and 0.90 (high x

series) 101

4.2.1 Structural characterization of high x series 114

4.2.1.1 X-ray diffraction 114

4.2.1.2 Back scattered images 115

4.2.2 Resistivity (p) vs. field (H) measurement of high x series 118 4.2.3 Dielectric measurements of high x series 119 4.2.4 Ferroelectric measurements of high x series 122 4.2.5 Magnetic measurements of high x series 123 4.2.6 Magnetoelectric measurements of high x series 126

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4.2.6.1 Magnetoelectric voltage coefficient (aE) vs. dc bias field (H)

measurement 126

4.2.6.2 Magnetization (M) vs. temperature (T) measurements 129

4.2.7 Conclusion 132

Chapter V: Two phase BaTiO3 - Co0

.6

ZnO

.4

Fe j

^.7

MnO

.3

04 composite 133

5.1 Structural characterization 133

5.1.1 X-ray diffraction pattern. 133

5.1.2 Scanning electron micrographs 135

5.2 Dielectric properties 136

5.3 Magnetic properties 141

5.4 Magnetoelectric measurements 143

5.4.1 Magnetoelectric voltage coefficient (aE) vs. dc bias field (H) plots 143 5.4.2 Magnetization (M) vs. temperature (T) plots 144

5.5 Conclusion 145

Chapter VI: Fe-implanted BaTiO3 single crystal 146

6.1 Dielectric measurement 147

6.2 Transmission electron microscopy 148

6.3 Magnetic measurements 150

6.3.1 Magnetization vs. temperature measurements 150

6.3.2 Exchange bias measurements 155

6.4 Conclusion 158

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Chapter VII: PbZro

^.⁵²

Ti0

^.48

03-Ni0

^.⁴

Zn0

^.^6-2g

Li gFe2+gO4 bilayered composite 159

7.1 Magnetoelectric measurements 161

7. 2 Conclusion 164

CHAPTER VIII: Conclusions & future scope 165

8.1 Summary 165

8.1.1 Three phase (BaTiO3-CoFe2O4-PVDF) composite 166 8.1.2 Two phase x PbZro.52Tio.4803-(1-x)Coo.6Zno.4Mno.3Fe1.704 composite

167 8.1.2.1 Composite series with x=0.65, 0.70, 0.75 and 0.80 167 8.1.2.2 Composite series with x=0.80, 0.85 and 0.90 169 8.1.3 Two phase (x) BaTiO3-(1-x)Coo.6Zno.4Mno.3Fe1.704 composite series where

x=0.50, 0.60, 0.70 and 0.80 169

8.1.4 Fe-implanted BaTiO3 single crystal 170

8.1.5 Two phase PbZro.52Tio.4803 - Nio.4Zno.6-2XLixFe2+XO4 bonded composites where

x=0.10, 0.15 and 0.20 171

8.2 Future scope 172

References Appendix

List of Publications Author's bio data

Certificate from International Centre for Diffraction Data

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LIST OF TABLE CAPTION CHAPTER-I

Table No. Title of the table Page No.

Table 1.1 ME voltage coefficients for few two phase ME composite systems.

26

CHAPTER-III

Table.3.1 Comparison of ME voltage coefficient (aE) reported in 70 literature for 2-phase sintered particulate composites of BT and

CFO with the highest value of aE obtained in present 3-phase particulate BT-CFO-PVDF composite.

CHAPTER-IV

Table 4.1 Lattice parameters of the component phases in composite 103 system [x PZT-(1-x) CZFMO] for x=0.65, 0.70, 0.75 and 0.80.

Table.4.2 Lattice parameters of the component phases of the composite 116 system [x PZT-(1-x) CZFMO] for x=0.80, 0.85 and 0.90.

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CHAPTER-V

Table 5.1 Lattice parameters of the component phases in composite system x BT-(1-x) CZFMO for x=0.50, 0.60, 0.70 and 0.80.

135

CHAPTER-VIII

Table 8.1 The best values of ME voltage coefficient (aE) from all 165 composite series studied in present thesis with the specified

method of measurement.

Synthesis and characterization of multiferroic composites