Structural, electric and magnetic study of Sm based
orthoferrites
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.
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.
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
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).
Structural, electric and magnetic study of Sm based orthoferrites
13
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).
12 Y. K. Jeong, Jung-Hoon Lee, Suk-Jin Ahn, and H. M. Jang, Solid State Commun. 152, 1112
(2012).
