SYNOPSIS OF

STRUCTURAL, OPTICAL, ELECTRICAL, MAGNETIC, AND

MAGNETOELECTRIC PROPERTIES OF UNDOPED AND DOPED

POLYCRYSTALLINE BISMUTH FERRITE

A THESIS

to be submitted by

B. RAMACHANDRAN

for the award of the degree

of

DOCTOR OF PHILOSOPHY

DEPARTMENT OF PHYSICS INDIAN INSTITUTE OF TECHNOLOGY MADRAS

CHENNAI 600036, TAMIL NADU, INDIA

AUGUST 2010

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1. INTRODUCTION:

The term multiferroism has been coined (Schmid 1994) to describe materials in which

two or three of the properties namely ferroelectricity, ferromagnetism, and ferroelasticity

occur in the same phase. Multiferroic materials are technologically and scientifically

promising because of their potential applications in data storage, spin valves, spintronics

and microelectronic devices (Tokura 2006). Bismuth ferrite, BiFeO3 is a single phase

multiferroics and it exhibit ferroelectricity with TC ≈ 1103 K, and antiferromagnetic

properties below TN ≈ 643 K (Fischer et al. 1980; Smolenskii et al. 1982).

There have been only a few investigations probing phonon properties in BiFeO3,

despite the fact that these studies can provide useful insight into microscopic properties

such as softening of dynamic ferroelectric modes, structure-property relations, different

behavior of local symmetry from the global symmetry in a nanoscale range, and the spin–

phonon coupling (Cho et al. 2000; Iliev et al. 1999). Additionally, there are considerable

discrepancies among the Raman scattering results reported on BiFeO3 single crystals and

epitaxially grown thin films, providing strong motivation for further studies (Haumont et

al. 2006; Fukumura et al. 2007; Cazayous et al. 2007). Cazayous et al. have studied the

effect of an electric field effect on the lattice response of a BiFeO3 single crystal by

Raman scattering. Recently, Kumar et al. 2008 and Singh et al. 2008 have reported

Raman studies of BiFeO3 thin film and single crystal, respectively. Recently, Kamba et

al. 2007 have studied frequency dependant dielectric properties of BiFeO3 ceramics over

a temperature range, 10-300 K. They observed an anomaly near 250 K in BiFeO3

ceramics, which was explained by Maxwell-Wagner contribution to the permittivity

(Kamba et al. 2007).

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2. AIM AND SCOPE OF THE WORK:

Main aim of this work is to identify a room temperature magnetoelectric multiferroic

material, and understand and investigate the physical properties such as structural, optical,

electrical, magnetic and magnetoelectric properties of the material for magnetoelectric

and magnetic field sensor applications. In order to achieve this aim, the following

objectives have been drawn;

Synthesis of single phase undoped and doped polycrystalline BiFeO3 ceramics.

Study of structural, optical, and electrical properties of polycrystalline undoped

and doped BiFeO3 ceramics.

Low temperature magnetic, dielectric and Raman spectroscopy studies of as-

prepared and vacuum annealed BiFeO3 ceramics to investigate coupling

between spin, charge and lattice order parameters.

Low temperature magnetic and dielectric properties of undoped and doped

BiFeO3 ceramics to investigate chemical pressure induced oxygen vacancy

effect on both magnetic and dielectric properties.

Magnetodielectric and magnetoelectric effect studies of undoped and doped

BiFeO3 ceramics at room temperature to envisage magnetoelectric and magnetic

field sensor applications.

3. DESCRIPTION OF RESEARCH WORK:

3.1 Single phase bismuth ferrite:

3.1.1 Structural properties of BiFeO3:

The phase formation of BiFeO3 ceramics sintered at 850 oC for 6 h was confirmed by

X-ray diffraction (XRD). Figure 1 shows the results of the Rietveld refinement of the

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XRD data of BiFeO3 sample. The refinement was carried out using the rhombohedral

crystal system with R3c space group. The refined lattice constants and volume of the unit

cell are a = b = 5.581 Å, c = 13.879 Å and V = 374.379 Å3, respectively. Field emission

scanning electron microscopy (FESEM) image (inset of Fig. 1) of the BiFeO3 pellet

shows the presence of micro-grains with sizes ~ 10 to 20 μm. Energy dispersive X-ray

analysis of BiFeO3 sample showed a Bi:Fe ratio of approximately 1:1.

Fig. 1 Rietveld analysis of the XRD pattern of BiFeO3 sample. The difference between observed

(Obs.) and calculated (Calc.) pattern is shown at the bottom of the Obs. and Calc. patterns. Inset

shows field emission FESEM image of BiFeO3 ceramic pellet.

3.1.2 Magnetic and magnetocaloric properties of BiFeO3:

Zero field cooled (ZFC) and field cooled (FC) measurements show small anomaly at

around 250 K which reveals the spin glass transition in polycrystalline BiFeO3 sample

(Fig. 2a). At 150 K, another anomaly is seen which may be due to spin reorientation as

observed in BiFeO3 single crystal (Redfern et al. 2008). Both ZFC and FC curves show

sudden rise in magnetization below 10 K, indicating a weak ferromagnetic nature in

polycrystalline BiFeO3. Fig. 2b shows magnetization (M) vs magnetic field (H) of

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BiFeO3 sample at 2 K and 300 K. At room temperature, the magnetization curve shows

antiferromagnetic nature. At 2 K, the magnetization curve exhibits weak ferromagnetism

with a coercive field of 2,433 Oe and it does not saturate even at a field of 5 T (top inset

of Fig. 2b). We also observed that the coercive field increases gradually below 150 K

which reaches a high value of 2,433 Oe at 2 K (bottom inset of Fig. 2b).

Fig. 2a) ZFC and FC magnetization measurements on BiFeO3 sample in a magnetic field of 50

Oe and 2b) Magnetization vs magnetic field curves of BiFeO3 in a magnetic field of 1 T at 2 K

and 300 K. Top inset in Fig. 2b shows high magnetic field (5 T) M-H plots of BiFeO3 at 2 K and

300 K, and bottom inset in Fig. 2b shows coercive field (Hc) versus temperature of BiFeO3.

The magnetic entropy change, ∆SM(T=Tav)∆H for an average temperature

Tav = (Ti+Ti+1)/2 from the two magnetization isotherms measured at Ti and Ti+1 in a

magnetic field changing by ∆H = H F-HI (HI and HF are the initial and final magnetic

field) at a constant step, δH, is given by the following equation (Pecharsky et al. 1999),

Where δMk=[M(Ti)k- M(Ti+1)k] is the difference in the magnetization at Ti and Ti+1,

δT= Ti-Ti+1 is the temperature difference between the two isotherms and n is number of

a)

b)

1

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( ) 22

n

M av H k nk

HS T M M MT

δ δ δ δδ

−

∆=

∆ = + +

∑

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points. Magnetic entropy change ∆SM(T=Tav)∆H was evaluated from the magnetization

data of BiFeO3 sample for the magnetic field change (∆H = 8T) in the temperature range

of 15–280 K in the step size δT = 5 K using a constant δH = 402 Oe and n = 200 (inset in

Fig. 3). Both the magnetic entropy change ∆SM(Tav)∆H and the combined error in the

magnetic entropy change of polycrystalline BiFeO3 sample are presented in Fig. 3. The

observed (five) peaks in the magnetic entropy change ∆SM(Tav)∆H and each peak

corresponding to low temperature transitions can be identified from elastic and electrical

anomalies in BiFeO3 single crystal and ceramics reported by Redfern et al., 2008.

Fig. 3 The magnetic entropy change, ∆SM(Tav)∆H vs temperature of polycrystalline BiFeO3 (BFO)

sample. Inset shows magnetization vs magnetic field of BFO at high magnetic field (8 T) in the

temperature range 15 to 280 K in steps of 5 K.

3.1.3 Low temperature dielectric and Raman spectroscopy studies of BiFeO3-δ ceramics:

In order to investigate the effects of oxygen non-stoichiometry on the electronic

structure and Fe valence in the as-prepared BiFeO3 (BFOAP) and vacuum annealed

BiFeO3 (BFOVA) ceramics, we performed X-ray photoelectron spectroscopy (XPS)

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studies. XPS measurements confirmed the presence of Fe only in 3+ (Fe3+) valence state

in both the as-prepared and vacuum annealed samples. To confirm that vacuum annealing

did introduce oxygen vacancies, we measured the O1s peaks in both samples. There is a

small shift in binding energy and broadening of O1s peak of BFOVA (530.7 eV)

compared to that of BFOAP (530.2 eV) has been observed, which establishes the creation

of oxygen vacancy defects in BFOVA sample.

Temperature dependent dielectric constant (εr) and dielectric loss (tan δ) measured at

30 kHz are shown for both samples (BFOAP and BFOVA) in Fig. 4a. We observe two

anomalies, at 25 K and 281 K, in the dielectric response of both BFOAP and BFOVA.

The anomaly at 281 K is considerably broader in the vacuum annealed sample as

compared to the as-prepared sample. We attribute the broadening of the high temperature

dielectric loss peak in the BFOVA sample to the additional disorder produced by oxygen

non-stoichiometry. The low temperature dielectric anomaly near 25 K may be due to a

magnetic glassy transition, which has been observed in BiFeO3 ceramics and single

crystals (S.A.T. Redfern et al. 2008). Our measurements of the dc magnetization and ac

susceptibility do not show any clear features associated with the 25 K anomaly, in either

BFOAP or BFOVA sample. Given this lack of any significant magnetic signature, we

suggest this low temperature feature may have resulted primarily from some structural

distortion, leading to a significant dielectric response. Frequency dependant dielectric

constant and dielectric loss of the BFOAP and BFOVA ceramics were measured at low

temperatures in the vicinity of this anomaly, with the dielectric loss plotted in Figs. 4b

and 4c. The peak temperature (Tp) shifts from 23.7 K to 31.9 K for BFOAP and from

24.4 K to 33.9 K for BFOVA as the frequency is varied from 10 kHz to 1 MHz.

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Fig. 4 a) Temperature dependent dielectric constant (εr) and dielectric loss (tan δ) of as-prepared

and vacuum annealed BiFeO3 (BFOAP and BFOVA) at 30 kHz, b) Frequency dependent

dielectric constant of BFOAP near 25 K, c) Frequency dependent dielectric constant of BFOVA

near 25 K and d) ln f vs 103/T plots of BFOAP and BFOVA.

In analyzing the dielectric relaxation, as shown in Fig. 4d, we found that the data fit

well to an Arrhenius expression, f = fo exp(E/kBT), where fo is the relaxation frequency, E

is the activation energy, and kB is the Boltzmann constant. The extracted activation

energies and relaxation frequencies of this dielectric relaxation process are found to be

29.6 meV and 1.24 x 1011 Hz for BFOAP and 34.3 meV and 2.20 x 1010 Hz for BFOVA,

respectively. This activation energy scale corresponds to approximately 340 K and 400 K

for BFOAP and BFOVA respectively. These activation energies are comparable to the

470 K activation barrier found in the case of the conventional relaxor ferroelectric

PbMg1/3Nb2/3O3 (Viehland et al. 1990). There is also a small linear shift in dielectric

constant with applied magnetic field at this anomaly, which indicates that a significant

magnetoelectric coupling is present in both BFOAP and BFOVA at 25 K.

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Figures 5a and 5b show the Raman spectra for as-prepared and vacuum annealed

BiFeO3 (BFOAP and BFOVA) recorded at temperatures ranging from 10 K to 100 K.

The peaks at 144, 178, 223 and 474 cm-1 can be assigned to the 4A1 modes and the eight

of the remaining peaks at 132, 264, 279, 295, 348, 371, 440, and 524 cm-1 are assigned to

the E modes (Cazayous et al. 2007). As per Cazayous et al., the mode around 552 cm-1

can be assign to the TO forbidden mode of the fourth A1 mode. The spectra plotted in

Figs 4a and 4b show a large number of modes for both samples, many of which evolve

with temperature. However, there are particularly striking changes in the E(TO4) and

A1(TO4) modes in both samples as the temperature is varied. The Raman shifts

associated with these modes are plotted as a function of temperature in Figs 5c and 5d.

Both the E(TO4) and A1(TO4) modes show very clear hardening near the 25 K anomaly,

with the peak frequency increasing by ~ 3 % for the E(TO4) phonon and by ~ 0.4 % for

the A(TO4) phonon. This hardening at the anomaly is considerably broader in the

vacuum annealed sample than that in the as-prepared sample. We attribute this

broadening to increased disorder in the oxygen deficient ceramic, which may be expected

to lead to broadening of the structural distortions, similar to the dielectric broadening

observed in the 25 K dielectric anomaly (see Fig. 4a). The Raman-silent A1(TO4) mode

is attributed to the presence of ferroelectric domains, where strain fields associated with

domain walls may make Raman forbidden phonons active (Cazayous et al. 2007). This

possible local structural distortion mediated dielectric and magnetic properties may be

due to strong coupling between magnetic and electric order parameters near 25 K.

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Figure 5 a) Raman spectra of as-prepared BiFeO3 (BFOAP) sample recorded in the temperature

range, 5 - 100 K, b) Raman spectra of vacuum annealed BiFeO3 (BFOVA) sample recorded in the

temperature range, 5 - 100 K, c) Temperature dependent relative Raman shift of 295 cm-1

(E(TO4)) and 552 cm-1 (A1(TO4)) modes of BFOAP near 25 K and d) Temperature dependent

relative Raman shift of 295 cm-1 (E(TO4)) and 552 cm-1 (A1(TO4)) modes of BFOVA near 25 K.

3.2 Barium and calcium doped bismuth ferrite:

3.2.1 Structural, magnetic, dielectric and magnetoelectric properties of undoped and

doped BiFeO3:

Synthesis of BiFeO3 (BFO), Bi0.9Ba0.1FeO3 (BB10FO), Bi0.9Ca0.1FeO3 (BC10FO) and

Bi0.9Ba0.05Ca0.05FeO3 (BB5C5FO) ceramics were carried out using ethanol mediated sol-

gel route. X-ray diffraction data of the BFO, BB10FO, BC10FO and BB5C5FO sintered

samples was refined with rhombohedral structure with space group R3c (Fig. 6). The

grain sizes of the doped samples were significantly reduced (~ 400-500 nm) compared to

that of undoped BFO (10-20 μm). Energy dispersive X-ray analysis of BFO, BB10FO,

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BC10FO and BB5C5FO ceramics indicated that the final compositions are close to that

of nominal composition. The evaluated lattice constants and unit cell volume of the

samples is tabulated (table 1).

Fig. 6 XRD patterns of a) BiFeO3 (BFO), b) Bi0.9Ba0.1FeO3 (BB10FO), c) Bi0.9Ca0.1FeO3

(BC10FO) and d) Bi0.9Ba0.05Ca0.05FeO3 (BB5C5FO) ceramics sintered at 850 oC for 6 h.

Table 1: Lattice constants and unit cell volume of undoped and doped samples.

Sample name Ionic radius (Å) a (Å) c (Å) Volume (Å)

BiFeO3 Bi3+ - 1.03 5.581 13.879 374.379

Bi0.9Ba0.1FeO2.95 Ba2+ - 1.35 5.569 13.767 369.803

Bi0.9Ca0.1FeO2.95 Ca2+ - 0.99 5.570 13.643 366.599

Bi0.9Ba0.05 Ca0.05FeO2.95 Ba2+ - 1.35, Ca2+ - 0.99 5.574 13.697 369.781

Magnetization (M-T and M-H) measurements of BC10FO and BB5C5FO samples

showed weak ferromagnetic behavior at 300 K, whereas M-H curves of BFO and

BB10FO samples showed antiferromagnetic behavior at 300 K. Ferroelectric hysteresis

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behavior was observed at room temperature in undoped and doped BiFeO3 samples. We

measured temperature and frequency dependant dielectric constant behavior of the

undoped and doped BFO samples at low temperatures in the vicinity of these anomalies,

as shown in Fig. 7. It is clearly seen that dielectric constant of doped samples is found to

increase compared to that of pure BiFeO3.

Fig. 7 Temperature and frequency dependant dielectric constant a) BiFeO3 (BFO), b)

Bi0.9Ba0.1FeO3 (BB10FO), c) Bi0.9Ca0.1FeO3 (BC10FO) and d) Bi0.9Ba0.05Ca0.05FeO3 (BB5C5FO)

samples. Insets show low temperature frequency dependant dielectric constant of the samples.

However, undoped and Ba doped BFO samples showed intrinsic behavior in the entire

measured temperature range (up to 350 K) whereas Ca doped and Ba-Ca co-doped BFO

samples showed high dielectric constants (>500) above 200 K, which can be due to

Maxwell-Wagner effects (Kamba et al. 2007). We observe two anomalies near 25 K and

281 K for pure BFO samples, whereas, these anomalies are found to shift to higher

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temperatures and also became boarder for the doped samples. The peak temperature (Tp)

at low temperatures (LT) has been found to shift to higher temperatures systematically as

the frequency is varied from 10 kHz to 1 MHz for all the samples, whereas, peak

temperature (Tp) at high temperatures (HT) shifts to higher temperatures for pure, Ca

doped and Ba-Ca co-doped BiFeO3 samples. However, the high temperature anomaly

near 280 K in Ba doped sample is found to disappear and it also becomes frequency

independent, as seen in fig. 7b.

Figure 10 Magnetic field dependant dielectric constant of a) BFO, b) BB10FO, c) BC10FO and

d) BB5C5FO samples at room temperature.

In order to find the activation energy (Ea) and relaxation frequency (fo) for both

relaxation behaviors of samples, we plotted ln f as a function of 103/T. Both activation

energy and relaxation frequency of doped samples were found to increase compared to

that of undoped BFO. The activation energy scale at LT corresponds to approximately

340 K, 1577 K, 1739 K and 1693 K for BFO, BB10FO, BC10FO and BB5C5FO samples,

respectively. These measurements suggest that the low temperature dielectric relaxation

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may be related to a relaxor-like ferroelectric behavior; however, the relaxing clusters

could be only weakly interacting.

In order to study the spin-charge coupling in the pure and doped BiFeO3 samples

at room temperature, we measured magnetic field dependence of dielectric constant at 30

kHz for BFO, BB10FO, BC10FO and BB5C5FO samples, as shown in Fig. 8. All doped

samples show practically distorted butterfly loops whereas undoped sample (BFO)

showed no signature of butterfly-like behavior. These measurements confirm that the

magnetodielectric effect in doped samples has been improved compared to pure BFO. A

negative magnetodielectric shift was found to be approximately 1.12 %, 0.03 %, 0.22 %

and 0.15 % in a magnetic field of 80 kOe for BFO, BB10FO, BC10FO and BB5C5FO

samples, respectively.

Fig. 9 a) Frequency dependant ME voltage (αEH) of undoped and doped BiFeO3 ceramics with

ac and dc applied fields of 1 Oe and 4 kOe and b) DC magnetic filed dependant magnetoelectric

voltage (αEH) of undoped and doped BiFeO3 ceramics with an ac applied of 1 Oe at 50 kHz.

Investigation of magnetoelectric (ME) effect of BFO, BB10FO, BC10FO and

BB5C5FO samples was carried out using a home made magnetoelectric effect setup. The

ME effect was measured in terms of the variation of the ME coefficient as a function of

a) b)

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frequency of ac magnetic field and bias dc magnetic field. The sample was put into a

small ac magnetic field (dH = 1 Oe) superimposed with dc magnetic field up to 4.5 kOe

in parallel. The transverse ME sensitivity was measured when the polarization direction

was perpendicular to the magnetic field. The frequency and magnetic field dependence of

the ME coefficients (αEH = dE/dH) of the undoped and doped BiFeO3 are shown in Figs.

9a and 9b. In particular, all the doped BiFeO3 ceramics exhibited a direct magnetoelectric

effect with a ME coefficient of the order of ~ 4-5 mV/cm Oe while undoped BiFeO3

ceramic showed a linear behavior which results from the magnetodielectric effect without

any magnetoelectric coupling.

4. SUMMARY OF THE WORK:

Single phase undoped and doped polycrystalline BiFeO3 ceramics were synthesized

using ethanol mediated sol-gel route.

Structural, optical, and electrical properties of polycrystalline undoped and doped

BiFeO3 ceramics were studied.

Investigation of low temperature magnetic, dielectric and Raman spectroscopy

properties of as-prepared and vacuum annealed BiFeO3 ceramics reveal coupling

between spin, charge and lattice order parameters in the BiFeO3.

Low temperature magnetic and dielectric properties of undoped and doped BiFeO3

ceramics were studied to investigate chemical pressure induced oxygen vacancy

effect on both magnetic and dielectric properties.

Room temperature magnetodielectric and magnetoelectric effect of undoped and

doped BiFeO3 ceramics were investigated for magnetoelectric and magnetic field

sensor applications.

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5. REFERENCES:

Cazayous M., D. Malka, D. Lebeugle, and D. Colson (2007) Electric field effect on

BiFeO3 single crystal investigated by Raman spectroscopy. Appl.Phys. Lett., 91, 071910.

Cho S.M., and H. M. Jang (2000) Softening and mode crossing of the lowest-frequency

A1(transverse-optical) phonon in single crystal PbTiO3. Appl. Phys. Lett., 76, 3014.

Fischer P., M. Polomska, I. Sosnowska, and M. Szymański (1980) Temperature

dependant of the crystal and magnetic structures of BiFeO3. J. Phys. C, 13, 1931.

Fukumura H., H. Harimaa, K. Kisodab, M. Tamadac, Y. Noguchic, and M.

Miyayama (2007) Raman scattering study of multiferroic BiFeO3 single crystal. J.

Magn. Magn. Mater., 310, e367-e369.

Haumont R., J. Kreisel, P. Bouvier, and F. Hippert (2006) Phonon anomalies and the

ferroelectric phase transition in multiferroicBiFeO3. Phys. Rev. B, 73, 132101.

Iliev M.N., A. P. Litvinchuk, H. G. Lee, C. L. Chen, M. L. Dezaneti, C. W. Chu, V.

Ivanov G., M. V. Abrashev, and V. N. Papov (1999) Raman spectroscopy of SrRuO3

near the paramagnetic-to-ferromagnetic phase transition. Phys. Rev. B, 59, 364-368.

Kamba S., D. Nuzhnyy, M. Savinov, J. Šebek, J. Petzelt, J. Prokleška, R. Haumont,

and J. Kreisel (2007) Infrared and terahertz studies of polar phonons and

magnetodielectric effect in multiferroic BiFeO3 ceramics. Phys. Rev. B, 75, 024403.

Pecharsky V. R. and K. A. Gschneidner, Jr (1999) Magnetocaloric effect from Indirect

measurements: Magnetization and heat capacity. J. Appl. Phys. 86, 565-675.

Redfern S.A.T., C. Wang, J. W. Hong, G. Catalan, and J. F. Scott (2008) Elastic and

electric anomalies at low temperature phase transitions in BiFeO3. J. Phys.: Condens.

Matter, 20, 452205.

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Schmid H. (1994) Multiferroic Magnetoelectrics. Ferroelctrics, 162, 317-338.

Smolenskii G.A., and I. Chupis (1982) Ferroelectromagnets. Sov. Phys. Usp, 25, 475.

Tokura Y. (2006) Multiferroics as quantum electromagnets. Science, 312, 1481-1482.

Viehland D., S. J. Jang, and L. E. Cross (1990) Freezing of the polarization

fluctuations in lead magnesium niobate relaxor. J. Appl. Phys., 68, 2916-2921.

PROPOSED CONTENTS OF THE THESIS

Chapter 1: Introduction.

Chapter 2: Sample synthesis and experimental details.

Chapter 3: Structural, optical, electrical, magnetic, and magnetodielectric properties

polycrystalline BiFeO3.

Chapter 4: Structural, optical, electric and magnetic properties polycrystalline Ba and

Ca doped polycrystalline BiFeO3.

Chapter 5: Magnetoelectric coupling studies of Ba and Ca doped polycrystalline

BiFeO3 ceramics for magnetoelectric and magnetic sensor applications.

Chapter 6: Summary and future scope of the work.

LIST OF PUBLICATIONS BASED ON THE RESEARCH WORK

1. B. Ramachandran, A. Dixit, R. Naik, G. Lawes and M.S. Ramachandra Rao,

Observation charge transfer and electronic transitions in polycrystalline BiFeO3, Phys.

Rev. B, 82 (2010) 012102.

2. B. Ramachandran and M.S. Ramachandra Rao, Low temperature magnetocaloric

effect studies in polycrystalline BiFeO3 ceramics, Appl. Phys. Lett., 95 (2009)

142505.

PRESENTATIONS IN CONFERENCES:

1. B. Ramachandran, A. Dixit, R. Naik, G. Lawes and M.S. Ramachandra Rao,

Electronic excitations and band structure of BiFeO3 ceramics, 18-22 January 2010,

11th Joint MMM-Intermag Conference (MMM 2010), Washington DC, USA.

2. B. Ramachandran, Brajesh Tiwari and M.S. Ramachandra Rao, Synthesis and

ferroelectric properties of BiFeO3, Indo-NUS workshops on current trends in physics,

28-01 Feb.-Mar. 2008, Indian Institute of Technology Madras, Chennai, India.