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Structural, electric and magnetic study of sm based

Structural, electric and magnetic study of Sm based

orthoferrites

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Dissertation First Phase Report submitted to

Department of Optoelectronics

University of Kerala, Thiruvananthapuram

Kerala-695581

Towards partial fulfillment for the degree of

Master of Technology in Electronics and Communication

(Optoelectronics and Optical Communication)

by

Dani Dileep

(Reg.No:OPE/MTech/ 16-06-03)

Work carried out under the guidance of

Dr.Anju Ahlawat

DST Inspire Faculty

at

Laser Material Section

Raja Ramanna Centre for Advanced Technology

Indore (M.P) – 452013

Government of India

Department of Atomic Energy

Raja Ramanna Centre for Advanced Technology

Indore (M.P.) – 452013

CERTIFICATE

This is to certify that the first phase work of dissertation entitled “Structural, electric

and magnetic study of Sm based orthoferrites” submitted by DANI DILEEP

(Reg.No:OPE/MTech/ 16-06-03) Department of Optoelectronics, University of

Kerala is a bonafide work carried out under my guidance and supervision at Laser

Materials Section, Raja Ramanna Centre for Advanced Technology, Indore (M.P).

Dr. Anju Ahlawat

DST Inspire Faculty

Laser Materials Section

Raja Ramanna Centre for Advanced Technology

Indore

DEPARTMENT OF OPTOELECTRONICS

UNIVERSITY OF KERALA

KARIAVATTOM

THIRUVANANTHAPURAM-695581

CERTIFICATE

This is to certify that the project report entitled “Structural, electric and Magnetic study of

Sm based orthoferrites” is a bonafide record of the first phase dissertation work carried out

by DANI DILEEP (Reg.No:OPE/MTech/16-06-03) towards the partial fulfillment of the

requirements for the award of the degree of Master of Technology in Electronics and

Communication (Optoelectronics and optical communication) under the University of

Kerala during the academic session 2016-2018.

…………………………

External Guide

Dr.Anju Ahlawat

DST Inspire Faculty

RRCAT, Indore

………………………

Head of the Department

Dr.K.G Gopchandran

Associate Professor

Dept.of Optoelectronics

University Of Kerala

………………………

Internal Guide

Dr.V.P Mahadevan Pillai

……………………

External Examiner

ACKNOWLEDGEMENT

First of all, I extend my heartfelt thanks to Almighty for keeping me fit for the successful

completion of this project.

I would like to express my heartfelt gratitude to my guide Dr. Anju Ahlawat for her

guidance “,encouragement, support and all valuable suggestions during this project. I would

also like to thank Dr.S.Satapathy for his regular support and valuable suggestions at all

stages of my project.

I am thankful to Dr. K. G. Gopchandran, Associate Professor and Head, Department of

Optoelectronics, University Of Kerala, for providing me the permission to do my project at

RRCAT, Indore.

I express my sincere gratitude to my internal guide Dr. V.P Mahadevan Pillai, Professor”,

Department of Optoelectronics, for patiently rendering his sincere and valuable guidance

throughout the project.

I would like to thank shri Pratik Deshmukh, shri Azam Ali Khan and Shri Prem Kumar

for their constant help during the project.

DANI DILEEP

ABSTRACT

The orthoferrites RFeO3 where R is a rare earth element and related compounds are being

studied because of their important technological applications and unusual magnetic and

electrical properties. Since the magnetic and electric properties are significantly dependent on

the shape, size of particles and the cation distribution, choosing the different methods of

preparation. Hence the magnetic and electric properties of these orthoferrites RFeO3 can be

modified by various ways either by doping A or B site with other ions or by changing size

etc. The orthoferrites RFeO3 with modified functional properties have wide range of

applications in magnetic recording, catalysis etc.

In the present work, we have optimized the synthesis of Sm based orthoferrite with doping

different rare earth ions on A site in SmFeO3. The effect of rare earth doping on the structure

of SmFeO3 is studied. Further, the effect of rare earth ions doping on electric and magnetic

properties of SmFeO3 will be studied.

CONTENTS

CHAPTER 1 INTRODUCTION

1

1.1 SmFeO3 2

CHAPTER 2 OBJECTIVE OF THE WORK 4

CHAPTER 3 LITERATURE REVIEW 5

CHAPTER 4 SAMPLE REPARATION 7

CHAPTER 5 CHARACTERISATION TECHNIQUES AND

RESULT

9

5.1 X-RAY DIFFRACTION 9

5.2 XRD PATTERN OF Gd DOPED SmFeO3 10

CHAPTER 6 CONCLUSION AND FUTURE WORK 11

LIST OF FIGURES

SERIAL NO. TITLE PAGE

NO.

1.1 Structure of an ideal perovskite 1

4.1 Flow chart for the synthesis of Gd doped

SmFeO3 nanoparticles by sol-gel method

8

5.1 Illustration of Bragg’s law 9

5.2 XRD pattern of Gd doped SmFeO3 samples at

varying doping concentrations of Gd

10

Structural, electric and magnetic study of Sm based orthoferrites

1

CHAPTER 1

INTRODUCTION

Recently, rare earth orthoferrites have attracted much greater attention because of their

interesting and perplexing magnetic properties. They are excellent candidates for application in

data storage devices and sensors. The rare earth orthoferrites are generally represented by the

formula RFeO3, where R is any rare earth element. Rare earth elements are a group of seventeen

elements in the periodic table consisting of lanthanides plus Scandium and yttrium. The ternary

oxides, RFeO3 have perovskite structure and are termed orthoferrites to distinguish them from

cubic spinel ferrites.

[1] Rare earth orthoferrites crystallizes in orthorhombic structure and most

of them are weakly ferromagnetic in nature. There are four iron ions and four rare-earth ions per

unit cell .The structure of an ideal perovskite is shown in Fig 1.1.

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Fig1.1: Structure of an ideal perovskite

The Fe3+ ion is octahedrally co-ordinated by oxygen forming an FeO6 octahedra. This structure

can be envisioned as corner linked FeO6 octahedra favouring a three dimensional polyhedral

network. The rare earth ions lie in the large cavities formed by these octahedra. The common

apex of two adjacent octahedra is the intervening anion that provides the super-exchange bond

between two iron ions. Thus each Fe3+ ion is coupled to the nearest six Fe3+ ions by the super

exchange bond, resulting in high Neel temperature (TN). Rare earth orthoferrites usually shows

complicated magnetic behaviour because of the presence of two magnetic ions (rare earth and

iron ions) in the system. The Fe3+ ions have antiferromagnetic ordering. Since the magnetic unit

cell symmetry is low, weak ferromagnetism is observed. At high temperature the Fe3+ ions

Structural, electric and magnetic study of Sm based orthoferrites

2

exhibit paramagnetic behaviour, upon cooing it orders antiferromagnetically at 600-700 K.

Canting of the magnetic moments results in weak ferromagnetism in the Fe3+ordered state..

[2]

Many rare-earth orthoferrites undergo spin-reorientation transitions upon further cooling “,where

the direction of the net magnetic moment rotates continuously or abruptly from one

crystallographic axis to another due to the antisymmetric and anisotropic-symmetric exchange

interactions between Fe3+and R3+.The magnitude of magnetic coupling between Fe-R and R-R is

much lower than that of Fe-Fe interaction. The various types of magnetic interaction between

Fe3+ and R3+ have the following hierarchical order: Fe–Fe, Fe–R and R–R with decreasing order

of strength.

In most of the orthoferrites there will be a change in the direction of easy axis of magnetization

from one crystallographic axis to another with the increase of temperature .These transitions are

referred to as spin reorientation transitions. In most of the orthoferrites, the easy direction of

spontaneous magnetization changes from the a axis to the c axis with the increase in temperature.

During this process, the magnetization stays in the ac plane, since the b plane is magnetically

hard

. [3]

These transitions can be described in two ways:

(1) The easy axis jumps abruptly in a first-order phase transition, possibly exhibiting thermal

hysteresis of the transition temperature;

(2) As the temperature is raised the easy axis starts to rotate at one definite temperature TL and

ceases rotation when it reaches a new orientation at another definite temperature TH. The second-

order phase transitions occur at TL and TH .

In orthoferrites, the spin-reorientation transition is observed to be of the second type and the net

moments of orthoferrites switches from c-axis to a-axis.

[1]

1.1 SmFeO3

Among the rare earth orthoferrites, SmFeO3 has excellent magnetic behaviour, with a band gap

of the semiconducting material of 2–3 eV. [4]. SmFeO3 has ABO3 type perovskite structure”,

where Sm3+ cations at the body centre and coordinate with twelve oxygen anions, while Fe3+

cations occupy the cube corner position and coordinate with six oxygen anions to form the

Structural, electric and magnetic study of Sm based orthoferrites

3

octahedron. The tilting of the octahedron mainly determines the magnetic properties of the

material in ABO3 structure.

The tilting or distortion in the structure can be explained through Goldschmidt tolerance factor

(t) which can be calculated from the following equation;

=

+

√ ( + )

where rA, rB and rO are the ionic radii of Sm3+ (1.24 Å), Fe3+ (0.645 Å) and O2- ion (1.35 Å)

respectively. In accordance with the Goldschmidt tolerance factor SmFeO3 adopts a distorted

orthorhombic perovskite structure and FeO6 octahedron is tilted towards the centre of the Sm

3+

ion to maintain the Sm3+- O2- bonding and this tilting mainly depends on the ionic radius of the

A-site cation, modifies the anisotropy and crystal field energies of Fe3+ ions, which in turn

influences the antiferromagnetic Neel temperature (TN).

[5] Dzyaloshinsky–Moriya anisotropic

exchange interaction is responsible for the improper ferroelectricity and weak ferromagnetic

behaviour in SmFeO3.[4] In this interaction, the magnetic moment of Fe3+ spins are not

completely antiparallel to those of the surrounding Fe3+ ions but rather are tilted by a small

angle, which leads to weak ferromagnetic behaviour. In rare earth orthoferrites the magnetic

properties arise due to the super exchange interaction of Fe3+–Fe3+, R3+–R3+ and R3+–Fe3+ via

O2_ ion [6].

SmFeO3 has got high magnetic ordering temperature (TN ~670 K)

[7] and the spin reorientation

transition occurs above the room temperature. The spin reorientation (SR) occurs at a

temperature between TSR1=450K and TSR2=480K, which is the highest spin reorientation

transition temperature of the whole RFeO3 family. The magnetostriction in SFO has a maximum

value near the SR temperature. Since the SR temperature lies above room temperature, SFO is of

particular interest for the magneto electric applications by utilizing its anomalous magnetoelastic

properties near SR temperature.[8]

Structural, electric and magnetic study of Sm based orthoferrites

4

CHAPTER 2

OBJECTIVE OF THE WORK

Recently, intensive research for multiferroic materials, mainly rare earth orthoferrites have been

carried out due to their promising applications in spintronics, sensor and catalysis applications.

Among the rare earth orthoferrites, SmFeO3 has the highest spin reorientation transition

temperature, which is above the room temperature. The functional properties for example

dielectric, magnetic properties etc. of SmFeO3 are sensitive to any change in lattice. Therefore

the doping of different rare earth elements at A or B sites could modify its functional properties.

In the present work we have studied the effect of doping the rare earth element Gadolinium (Gd)

on the structural and functional properties of SmFeO3.

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Structural, electric and magnetic study of Sm based orthoferrites

5

CHAPTER 3

LITERATURE REVIEW

As discussed in previous section, different functional properties for example dielectric, magnetic

etc. of SmFeO3 are sensitive. The doping of different rare earth elements at A or B sites could

modify its functional properties. Few examples are described below.

Xiaoxiong Wang et.al (2017) had studied the effects of Er3+doping on the lattice structure”,

magnetic and ferroelectric properties of SmFeO3.Structural analysis of Erbium doped SmFeO3

shows a reduction in the lattice constant .Upon doping “,the smaller ionic radius of Er3+ ions

causes the peaks to shift to higher angles indicating that the interplanar spacing become smaller

and also the distortion become much more significant after doping .Among the rare earth

orthoferrites”,SmFeO3 has got the highest spin reorientation temperature. They also studied the

magnetic properties of Er3+ doped SmFeO3.It was observed from the magnetic hysteresis loop

that the coercive field value increases at low temperatures. [9] The enhancement of coercive field

at low temperature was attributed to exchange interaction between the polycrystalline grains.[10]

An overall increase in magnetic susepctibility and magnetic saturation was observed due to high

spin number of Er3+ion. Ferroelectric measurements were done at room temperature and it was

observed that the ferroelectricity of the system decreased with doping.

Shahid Husain, Ali O. A. Keelani (2017) studied the structural properties of Mn doped

SmFeO3.The samples were prepared by solid state reaction. XRD patterns revealed that the

samples are in single phase and have orthorhombic crystal structure. A slight decrease in lattice

parameter and unit cell volume with increase in Mn concentration is observed as the ionic radius

of Mn3+ is less than that of Fe3+. Mn doping at the Fe3+ site results in a distortion in the FeO6

octahedron. This distortion induces strain in the lattice, which results in the shifting of peak

towards higher values of 2θ. The strain and stress induced in the lattice were estimated using the

Williamson- Hall analysis. It is observed from the analysis that the crystallite size, lattice strain

and stress increases with increase in doping concentration.

Structural, electric and magnetic study of Sm based orthoferrites

6

Huazhi Zhao et.al (2013) reported the Ti-doping effects on the total magnetization of perovskite

SmFe1-x Tix O3 samples with x= 0.1, 0.2, and 0.3. Structural properties of the samples were

analyzed by Raman spectroscopy and XRD. It is observed that as the doping concentration of Ti

increases the lattice parameter b decreases and the oxygen octahedron is compressed along the b

axis. Thus Ti doping induces distortion in the lattice.[11] The Ti ions with empty d shell replaces

Fe ions with partially filled d shell. As the doping concentration increases, the total number of d

electrons in the sample decreases and Fe sublattice is diluted by the Ti doping. A strong interplay

between Sm-4f and Fe-3d electrons happens due to Ti doping, which weakens the total

magnetization and considerably suppresses the weak ferromagnetism of Fe sublattice starting

from 260 K.[12]

Structural, electric and magnetic study of Sm based orthoferrites

7

CHAPTER 4

EXPERIMENTAL TECHNIQUES

4.1 SAMPLE PREPARATION

 Sol-gel synthesis of Gd doped SmFeO3

Nanomaterials have extremely small size, having at least one dimension in the range of 100 nm

or less. These materials attained much attention in the recent years by virtue of their unusual

optical, electrical, mechanical and magnetic properties. These materials can be prepared in

different ways. The two main approaches for the preparation of nanoparticles include the top-

down approach and bottom- up approach. In top–down approach, the bulk materials disassemble

into finer particle, while in bottom–up approach the atoms or molecules arrange themselves in a

specific way to create the material. In the present work all the required samples are prepared by

a bottom–up approach, sol-gel autocombustion method where the particles aggregate together to

form a network.

In Sol-gel process the evolution of inorganic network occurs through the formation of a

colloidal suspension (sol) and gelation of the sol to form a network in a continuous liquid phase

(gel). Subsequent combustion of the aqueous solution after the formation of the gel yields a

voluminous and fluffy product with large surface area. In this technique the vital elements for the

combustion process include oxidizing metal salt and combustion agent. The flow chart for the

synthesis of Gd doped SmFeO3 is shown in fig4.1.

In the present work Iron (III) Nitrate Nonahydrate [Fe (NO3)3.9H2O] was used as the

oxidizing metal salt and glycine serves as fuel during the reaction, being oxidized by nitrate

ions. Nitrates are chosen as metal precursors, not only for providing the metal ion, but also

because of their great water solubility, allowing a greater homogenization. The samples at

varying doping concentrations were prepared by mixing the calculated amount of Sm2O3″,Gd2O3″,

Fe(NO3)3.9H2O and glycine in a beaker and then heating it at 180°C till gellification happens.

After the formation of the gel, the temperature is increased to 220°C till fluffy powder is formed.

The combustion can be considered as a thermally induced redox reaction. The energy relaesed from

the exothermic reaction is high enough for the formation of fine particle. The generation of gases

also helps to limit interparticle contact, resulting in a more powdery product.

Structural, electric and magnetic study of Sm based orthoferrites

8

Fig 4.1: Flow chart for the synthesis of Gd doped SmFeO3 nanoparticles by sol-gel method

The main advantages of sol-gel method are:

 Low temperature process.

 Uses a solution at the initial step so that the reactants are well dispersed, providing a

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homogeneous mixture.

 The crystalline size of the final product will be in the nanometer range.

 Better control of stoichiometry.

 Exothermic reaction produces the product instantaneously.

Structural, electric and magnetic study of Sm based orthoferrites

9

CHAPTER 5

CHARACTERISATION TECHNIQUES AND RESULT

5.1 X-RAY DIFFRACTION

X-ray diffraction is a versatile and non-destructive technique for the study of crystal structures

and atomic spacing. X-rays having wavelength in the range of 0.5-2.5Å are used for diffraction.

Powder XRD is a rapid analytical technique primarily used for phase identification of a

crystalline material and can provide information on unit cell dimensions and size of the particles

in the sample. The basic principle behind X-Ray diffraction is the Bragg’s Law, which gives us

the geometrical conditions under which a diffracted beam can be observed.

Fig 5.1: Illustration of Bragg’s Law

Fig 5.1 shows the rays diffracted from different lattice planes and in order for constructive

interference, the path difference should be an integral multiple of wavelength. Bragg’s law can

be expressed as

2dSinθ = nλ

Where λ is the wavelength of the X-rays, d is the inter planar spacing and θ is the Bragg’s angle.

The value of n in Bragg’s law is always taken as unity. This law relates the wavelength of

electromagnetic radiation to the diffraction angle and the lattice spacing in a crystalline sample.

These diffracted X-rays are then detected, processed and are converted to a count rate which is

then output to a device such as a printer or computer monitor.

Structural, electric and magnetic study of Sm based orthoferrites

10

Each crystalline material has a set of unique d-spacing. Identification of the crystalline sample is

achieved by the conversion of the diffraction peaks to d-Spacing. This is achieved by comparison

of d-spacing with standard reference patterns.

5.2 XRD PATTERN OF Gd DOPED SmFeO3

XRD pattern of the Gd doped SmFeO3 samples with varying doping concentrations of Gd (0.2″,

0.4, 0.6, 0.8), which are calcined at 800°C is shown in Fig5.2.

Fig 5.2: XRD pattern of Gd doped SmFeO3 samples at varying doping concentrations of Gd

It is observed from the XRD pattern that the samples obtained after calcination at 800°C are of

pure phase with orthorhombic structure which are in accordance with the standard data (JCPDS

NO.: 74-1474 ). No other characteristic peaks of impurities were detected. A slight shifting of the

peak towards the higher angles is observed from the pattern. Gd has got smaller ionic radius

(2.38Å) when compared to Sm (2.42Å). Doping of Gd 3+ ion having smaller ionic radius results

in the shifting of peak towards higher angles. This indicates that the interplanar spacing become

smaller and also the distortion become significant after doping.

Structural, electric and magnetic study of Sm based orthoferrites

11

CHAPTER 6

CONCLUSION AND FUTURE WORK

In the present work we have analyzed the structural characteristics of Gd doped SmFeO3.It is

observed that no other characteristic peaks for impurities were detected. Slight shifts in the peak

towards higher angles were observed, which reflects the decrease in lattice parameter. This also

indicates significant distortion in the structure of SmFeO3 after doping Gd. In future the

functional properties of the samples such as dielectric analysis, magnetization measurement etc.

will be analysed.

Structural, electric and magnetic study of Sm based orthoferrites

12

REFERENCES

1 S.C. Parida, S.K. Rakshit, Ziley Singh, “Heat capacities, order–disorder transitions, and

thermodynamic properties of rare-earth orthoferrites and rare-earth iron garnets”, Journal of

Solid State Chemistry 181 (2008) 101–121.

2 R.G. Burns, in: A. Navrotsky, D.J. Weidner (Eds.), Geophysical Monograph 45, “ Perovskite:

A Structure of Great Interest to Geophysics and Materials Science”, American Geophysical

Union”,Washington, DC, 1981, p. 81.

3

T. Yamaguchi, “Theory of Spin Reorientation Rare -Earth orthochromites and orthoferrites””,

J. Phys. Chem. Solids. 1974, Vol. 35. pp. 479-500.

4 Subramanian Yuvaraja, Samar Layek, S. Manisha Vidyavathy, Selvaraj Yuvaraj, Danielle

Meyrick, R. Kalai Selvan”,, “Electrical and magnetic properties of spherical SmFeO3 synthesized

by aspartic acid assisted combustion method”, Materials Research Bulletin 72 (2015) 77–82.

5 Zhiqiang Zhou , Li Guo , Haixia Yang , Qiang Liu , Feng Ye , “Hydrothermal synthesis and

magnetic properties of multiferroic rare-earth orthoferrites”, Journal of Alloys and Compounds

583 (2014) 21–31.

6 Adhish Jaiswal, Raja Das, Suguna Adyanthaya, and Pankaj Poddar, “Surface Effects on

Morin Transition, Exchange Bias, and Enchanced Spin Reorientation in Chemically Synthesized

DyFeO3 Nanoparticles”, J. Phys. Chem. C (2011), 115, 2954–2960.

7 E. N. Maslen, V. A. Streltsov, and N. Ishizawa, Acta Crystallogr. Sect. B52, 406 (1996).

8 Anju Ahlawat”,S. Satapathy, V. G. Sathe”,R. J. Choudhary, and P. K. Gupta, “Strong

magnetoelectric and spin phonon coupling in SmFeO3/PMN-PT composite” applied physics

letters 109, 082902 (2016).

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9 Xiaoxiong Wang, Jing Yu, Jun-cheng Zhang, Xu Yan, Chao Song, Yunze Long, Keqing Ruan”,

Xiaoguang Li, “Structural evolution, magnetization enhancement, and ferroelectric properties of

Er3+-doped SmFeO3”, Ceramics International (2017).

10 J. Goodenough, “A theory of domain creation and coercive force in polycrystalline

ferromagnetics”, Phys. Rev. 95 (1954) 917.

11 Huazhi Zhao, Shixun Cao, Ruoxiang Huang”,Wei Ren”,Shujuan Yuan”,Baojuan Kang, Bo Lu”,

and Jincang Zhang, “Enhanced 4f-3d interaction by Ti-doping on the magnetic properties of

perovskite SmFe1-xTixO3””,Journal of applied physics 114, 113907 (2013).

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