Ghulam Ali

Supervisor: Prof. Dr. S. A.

Siddiqi

Presenter:

Centre of Excellence in Solid State Physics

University of the Punjab, Lahore

Preparation and Characterization of doped Multiferroic Materials

11-04-2010

Outline

oMultiferroicsoBiFeO3

oHistory

oWhy Bi0.9La0.1Fe1-xCoxO3

oExperimentoResults and Discussion o Conclusion

2

Multiferroic

multi ferroic

More than oneFerromagnetic, ferroelectric, ferroelastic 3

• Multiferroic Materials possess two or more of the following

• (Anti-)Ferromagnetism, (Anti-)Ferroelectricity, (Anti-)Ferroelasticity

E

Hσ

M

P

εMagnetoelectric

ity

Magnetoelasticity

Piezoelectricity

χE

χMS

d α

Introduction to Multiferroics

• Coupling between order parameters

N. A. Spaldin and M. Fiebig, Science 309, 391 (2005).

4

ApplicationsSpintronics Devices (that includes a spin-based transistor)

Information Storage Devices (magnetic tape, floppy disk etc)

Spin Valve (device consisting of two or more conducting magnetic materials, that alternate its electrical resistance)

Quantum Electromagnets (electromagnets are wire coils or loops, which tend to be bulky and difficult to fabricate)

Microelectronic Devices (MOSFETs, Bipolar Transistor etc)

Sensors (measures a physical quantity and converts it into a signal which can be read by an instrument)

Spaldin N A and Fiebig M 2005 Science 309 391

5

D. Khmoski

Some common Multiferroic with their Tc, TN and Polarization

6

Among all above BiFeO3 is the only material that is both magnetic and strong ferroelectric at room

temperature.

As a result, it has had an impact on the field of multiferroics that is comparable to that of yttrium

barium copper oxide(YBCO) on superconductors, with hundreds of publications devoted to it in the past few

years.

G.Catalan and J. F. Scott 20097

BiFeO3

1. Distorted Rhombohedral Structure2. Point Group R3c3. Perovskite type unit cell with arh =

3.965Å and αrh=89.3°

4. Room temperature Polarization is along [111]

G. catalan and F. Scot 2009

8

Fe

Bi

2P

3P

1P

4P

2P

1P

4P

3P

(001)

AFM Ordering

FE Ordering

Polarization points in one of 8 possible <111> directions.

Magnetic plane is perpendicular to the

polarization direction.

P

Bi

Fe

O

M

M

BiFeO3, Polarization and Magnetization

TC ~ 1103KTN ~ 643K

Ederer and Spaldin, PRB 71(2005)9

History P. Curie (1894) Crystal could be ferroelectric and ferromagnetic simultaneously. J. Valasek (1920) Discovered the switching in ferroelectrics. Peter Debye (1926) Magnetoelectric (ME) effect. Wigner (1932) Gives time reversal symmetry R, RH=-H, RE=E. Dzyaloshinsky (1959) True magnetoelectrically defined free energy was understood theoretically

in Cr2O3 that is G (P, M, T) =αijPiMj -, Astov (1960) Discovered magnetoelectric experimentally in Cr2O3 material. H. Schmid (1994) Gives the name Multiferroic as the material possess two of the ferroic

properties simultaneously.

G. Catalan and J. F. Scott Advance Materials 2009

10

Why Bi0.9La0.1Fe1-xCoxO3 ?

Where x=0, 0.03, 0.05, 0.07, 0.09

11

Effect of La doping

1. La doping contents indicate that it stabilize the structure of BiFeO3 while the mechanism for the stabilization of BiFeO3 by La doping is not known and also leakage current can be reduced at high applied fields by adding a small amount of La doping.

Ju Hong Miao et al J.Am.Ceram.Soc.92 (2009)

2. It was established that even a small fraction of rare-earth (La) additives significantly increases the magnetoelectric and magnetodielectric affects at room temperature.

A. A. Amirov et al Technical Physics Letters, 2008

12

Effect of Co doping

The magnetic property of BiFeO3 are greatly enhanced due to Co ions doping at Fe sites.

Yonggang Wang et al Material Letters (2008)

The undoped BiFeO3 was antiferromagnetic but with the subsitution of Co it becomes ferromagnetic.

Feridoon Azough et al. Journaln of European Ceramin Society (2010)

Addition of Co improve significantly the ferromagnetic properties of bulk BiFeO3.

Hai-Xia Lu et. Al. Progress in Electromagnetic Research symposium, China, (2008)

13

Experimental Procedure

Sol-gel auto combustion route is adopted to prepare BiFeO3.

Raw materials are Fe(NO3)3.9H2O, 4BiNO3(OH)2.BiO(OH) and La(NO3)3.6H2O.

Dissolved in 75ml of distilled water with addition of Metal nitrate to Glysin in 1:1

14

Sol gel auto-combustion method Sol-gel auto-combustion method is one of the most

widely used methods to prepare the BFO like materials. Citric acid, glycine or urea is used as fuel agent in this

chemical reaction method.

15

Self-purification due to the high exothermic temperatures involvement.

To obtain the products in the desired size and shape.

Simple and cost effective. To get the homogeneous and very fine

crystalline nano-powders. Synthesis of single phase materials at very

low temperatures and short reaction times.

ExperimentalPure and Co doped Bi0.9La0.1FeO3 (Bi0.9La0.1Fe1-xCoxO3, x = 0, 0.03, 0.05, 0.07, 0.09) samples were synthesized using sol gel auto-combustion method. Lanthanum nitrate, bismuth subnitrate, and iron nitrate were taken in appropriate ratios.

4BiNO3(OH)2.Bi(OH) Fe(NO3). 9H2O

Mixed solution in deionized water

Glycine

Heated on a hot plate at 120-1300C with magnetic stirring

Viscous gel

CombustionFluffy powder is

heated for 30 minutes at 1300C

La(NO3)3. 6H2O

Flow chart of experimental

method

16

Results and Discussions

17

The phase identification in powder form was performed on an

X-ray diffractometer (X’PERT PRO of PANalytical Company Ltd., Holland) with Cu Kα radiation. Fig. 1 shows the XRD pattern of Bi0.9La0.1Fe1-xCoxO3 (x =

0, 0.03, 0.05, 0.07, 0.09) samples. No impurity phase was detected in the composition

with x = 0. The only peak observed for Bi2Fe4O9 impurity phase

has been marked by (*) on these diffraction patterns.

18

Figure 1 XRD patterns of all compounds of Bi0.9La0.1Fe1-XCoXO3 (for x = 0, 0. 03, 0.05, 0.07, 0.09). The

impurity phase (Bi2Fe4O9) peak is marked with *. The hkl values of Bi0.9La0.1FeO3 were matched with X.Zheng et al. J.of Alloy and Compound 499(2010)

20 30 40 50 60 70

22

02

08

30

02

14

01

81

221

160

24

20

2

11

0

10

4

In

ten

sit

y (

arb

. u

nit

s)

2(Degree)

X = 00

12

19

20 30 40 50 60 70

Inte

nsi

ty (

arb

. un

its)

2(Degree)

X = 0.03

20 30 40 50 60 70

Inte

ns

ity

(a

rb.

un

its

)

2(Degree)

X = 0.05

20 30 40 50 60 70

Inte

ns

ity

(a

rb.

un

its

)

2(Degree)

X = 0.07

20 30 40 50 60 70

Inte

ns

ity

(a

rb.

un

its)

2(Degree)

X = 0.09

Calculation of Crystallite Size• The crystallite size is calculated by Scherrer formula which is

t =kλ/BcosѲB and instrumental broadening is not subtracted.

• where, k is constant with value 0.94, λ is wavelength with 1.542Å, B is full width half maximum and ѲB is Bragg angle.

20Figure 2 Crystallite size (in nanometer) versus doping concentration with X = 0, 3,5,7,9 percent.

-1 0 1 2 3 4 5 6 7 8 9 10

18

20

Cry

stal

lite

size

(nm

)

Doping concentration in %

The lattice parameters “a” and “c” of the hexagonal unit cell were calculated using the equationSin2θ = λ2/3a2(h2 + hk + k2) +λ2l2 /4c2 The strongest peaks (012) and (110) were employed for such calculations.The lattice parameters a and c, the volume of hexagonal unit cell V, and the ratio c/a are listed in Table 4.1 and are in good agreement with values reported by X.Zheng et al. J. of Alloy and Compound 499(2010).

Compositions a(Å) c(Å) c/a V(Å3)

Bi0.9La0.1FeO35.5872 13.7077 2.4534 370.5706

Bi0.9La0.1Fe0.97Co0.03 O35.6601 13.8359 2.4445 383.8606

Bi0.9La0.1Fe0.95Co0.05 O35.7309 13.5610 2.3663 385.705

Bi0.9La0.1Fe0.93Co0.07 O35.7166 13.7134 2.3989 388.0955

Bi0.9La0.1Fe0.91Co0.09 O35.7149 13.7576 2.4073 389.1149

Table 1 Lattice parameters (a, c), ratio c/a, and volume of hexagonal unit cell is shown for the samples of Bi0.9La0.1Fe1-XCoXO3 (for x = 0, 0. 03, 0.05, 0.07, 0.09). 21

MAGNETIZATION MEASUREMENTMagnetic properties were investigated using Lake Shore-7407, vibrating sample magnetometer

-5000 -2500 0 2500 5000

-4

-2

0

2

4

Mag

netiz

atio

n (e

mu/

g)

Magnetic field (Oe)

x = 0 x = 0.03 x = 0.05 x = 0.07 x = 0.09

M-H loops of Bi0.9La0.1Fe1-XCoXO3 (for x = 0, 0.03, 0.05, 0.07, 0.09) samples.

For undoped sampleMs = 0.98 emu/g and

Hc = 57 Oe For x = 0.09

Ms = 4.18 emu/g and Hc = 220 Oe

22

17.5 18.0 18.5 19.0 19.5 20.00.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Ms (

em

u/g

)

Estimated crystallite size (nm)

Saturation magnetization plotted against estimated crystallite size of Bi0.9La0.1Fe1-

XCoXO3 (for x = 0.09, 0.07, 0.05, 0.03, 0) samples respectively

Saturation magnetization

increases with the decrease of

crystallite size. The saturation

magnetization also increases with the concentration of cobalt which is in

good agreement as reported in literature.

23

Microstructural analysis of Bi0.9La0.1Fe1-XCoXO3 (for x = 0, 0.03, 0.05, 0.07, 0.09) samples were carried out by using S-3400N SEM HITACHI EMAX scanning electron microscope operated

at 30.00kV in its secondary electron image mode.

24

Figure 3: SEM images of the Bi0.9La0.1Fe1-xCoxO3 (x = 0, 0.03, 0.05, 0.07, 0.09) samples at magnification of 5.00 × K.

25

The morphology of all these samples is almost similar. Two types of grains

can easily be identified. Larger volume of the sample comprises of the larger sized well shaped grains ( ~ 5 μm) and a small proportion of

grains consists of well defined shaped equi-axed crystals with

0.5 μm size.

Dielectric constant, loss factor, and tangent loss measurements of Bi0.9La0.1Fe1-XCoXO3 series have been carried out in the frequency range from 20 Hz to 1M Hz at room temperature by using 1920 Precision LCR

Meter manufactured by QuadTech.

10k 100k 1M0

50

100

150

200

250

300

350

400

450

500

550

Die

lectr

ic c

osta

nt (/ )

log f (Hz)

X = 0.09 X = 0.07 X = 0.05 X = 0.03 X = 0

(a)

10k 100k 1M

0

20

40

Ta

ng

en

t o

f d

iele

ctri

c lo

ss a

ng

le (

tan)

log f (Hz)

X = 0.09 X = 0.07 X = 0.05 X = 0.03 X = 0

(b)

10k 100k 1M

0

1000

2000

3000

4000

5000

6000

7000

Die

lectr

ic lo

ss fa

cto

r (// )

log f (Hz)

X = 0.09 X = 0.07 X = 0.05 X = 0.03 X = 0

(c) Figure 4 (a) Dielectric constant (ε'), (b) Tangent of dielectric loss angle (Tanδ), and

(c) Dielectric loss factor (ε'') are shown against log f (Hz). Colored lines with

different symbols shows different concentration as mentioned in small box on

the top-right of the figures.26

The temperature dependent DC electrical resistivity of the Bi0.9La0.1Fe1-XCoXO3 (for x = 0, 0. 03, 0.05, 0.07, 0.09) samples was

evaluated by using a Two Point Probe set up.

150 200 250 300 350

0.0

2.0x103

4.0x103

6.0x103

8.0x103

Re

sis

tivity (

M-c

m)

Temperature (C)

x = 0 x = 0.03 x = 0.05 x = 0.07 x = 0.09

Compositions Volume resistivity (Ω-

cm)

Bi0.9La0.1FeO31.6333 x 109

Bi0.9La0.1Fe0.97Co0.03 O34.3556 x 108

Bi0.9La0.1Fe0.95Co0.05 O39.1467 x 108

Bi0.9La0.1Fe0.93Co0.07 O31.2815 x 109

Bi0.9La0.1Fe0.91Co0.09 O39.0462 x 108

Table 2: Volume resistivity (Ω-cm) of samples Bi0.9La0.1Fe1-

XCoXO3 (for x = 0, 0. 03, 0.05, 0.07, 0.09)

at room temperature.

Figure 4.6 Resistivity (MΩ-cm) against temperature (˚C) of the samples Bi0.9La0.1Fe1-XCoXO3 (for x = 0, 0. 03, 0.05, 0.07,

0.09). 27

In order to study the Ferroelectric behavior of Co doped Bi0.9La0.1FeO3 multiferroic, manually designed Sawyer-Tower circuit was used to measure ferroelectric hysteresis loop. All the measurements were taken at room temperature and a maximum of 100KV/m field was applied. Hysteresis loops for Bi0.9La0.1Fe1-xCoxO3 (x = 0, 0.03, 0.05, 0.07, 0.09) are shown in Figure 6.

28

Figure 6 P-E loops for Bi0.9La0.1Fe1-xCoxO3 (x = 0, 0.03, 0.05, 0.07, 0.09) samples and table with Coercive field and Saturation Polarization.

Compositions Coercive field

Ec (KV/m)

Saturation polarization

(μC.cm-2)

Bi0.9La0.1FeO349 0.0508

Bi0.9La0.1Fe0.97Co0.03 O355 0.0184

Bi0.9La0.1Fe0.95Co0.05 O380 0.0393

Bi0.9La0.1Fe0.93Co0.07 O345 0.0246

Bi0.9La0.1Fe0.91Co0.09 O373 0.0477

Conclusion

29

An impurity phase of Bi2Fe4O9 was detected in all the Co doped compositions.

Lattice parameters and crystallite size were significantly changed with the substitution of Co at the Fe sites.

For x = 0, the estimated crystallite size was 19.76 nm, decreases with cobalt concentration and for x = 0.09, it became 17.58 nm.

The saturation magnetization and coercive field for undoped sample was observed as low as Ms = 0.98 emu/g and Hc = 57 Oe respectively and both these saturation magnetization and coercive field increases with cobalt concentration and becomes Ms = 4.18 emu/g and Hc = 220 Oe for x = 0.09.

30

The dielectric constant for undoped sample is found 540 at log 2, decreases with the increase in frequency and becomes 148 at log 5.5.

The dielectric constant also decreases with increasing cobalt concentration and found 312 at log 2 for x = 0.09 composition and then decreases with frequency and becomes 11.93 at log 5.5.

The un-doped sample showed a maximum value of resistivity of 8.40 × 109 Ω-cm at 160˚C, which decreased gradually with the increase in temperature and became 1.11 x 106 Ω-cm at a temperature of 350 ˚C.

The values of resistivity were decreased as the amount of Co contents was increased and becomes 0.16 × 109 Ω-cm at 160˚C for x = 0.09.

P-E loops provide a clear indication of the ferroelectric behavior of the both undoped and Co doped Bi0.9La0.1FeO3.

The saturation polarization has been found maximum for un-doped sample (0.0508 μC.cm-2) which is very low compared to the literature.

THANK YOU

31