TRANSPORT PHENOMENA AND MAGNETIC/CRYSTALLINE...
Transcript of TRANSPORT PHENOMENA AND MAGNETIC/CRYSTALLINE...
TRANSPORT PHENOMENA AND
MAGNETIC/CRYSTALLINE
STRUCTURE OF MANGANITES
Presented by:
1. Hatem Mohamed Saad (Al Azhar University); 2. Ahmed El Ghazaly (The American University in Cairo); 3. Ahmed Hassan (Suez Canal University); 4. Mohamed Ahmed Ashmawy (Ain Shams University).
Supervisor : Dr . Vitalii Turchenko
Frank Laboratory of Neutron Physics
Joint Institute for Nuclear Research
Russia
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2
1 – Сa ;
2 – Ti ;
3 – O;
ABO3
A – rare-earth ions: La, Sm, Pr… and Ca, Sr, Ba, Pb…
B – transition metals: Mn, Cr, Fe…
Ideal Pervoskite Structure
Introduction Objectives Experimental
procedure
Results
CaTiO3
1950 – Jonker G. H., Van Santen J. H. Physica. Vol.16. (1950).
1) Chemical composition influence onto the type of crystal structure
PM
FM
AFM
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δ=0
0<δ<0.15
0.15≤ δ
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J.F. Mitchell et al. Phys. Rev. B 54, p.6172, (1996);
В.С. Захвалинский и др. ФТТ, т. 48, с.2175, (2006).
Zhen Fan et all, Scientific Reports 4, 2014
acb
O
2
:'
acb
O
2
:*
LaMnO3
+δ
Orthorhombic
Pseudo-cubic
Rhombohedral
Introduction Objectives Experimental
procedure
Results
LaMnO3+δ
cR3
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2) Oxygen stoichiometry
Conduction Mechanism
Double exchange
interaction
Transport properties depend on
• Transfer of electrons between Mn3+ and Mn4+ cations, via oxygen 2p orbitals
• The relative Mn3+/Mn4+ concentrations
• Strong coupling between t2g and eg for example: in Mn3+ very strong hybridized with oxygen 2p orbitals
• Mn-O-Mn Angle controlled by equation
Transport Phenomena
La1-xSrxMnO3
Re
sis
tiv
ity
(Ω
*cm
)
Temperature (K)
Introduction Objectives Experimental
procedure
Results 5
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1994 – the discovery of magnetoresistive effect in La-Ca-MnO films
Jin S., Tiefel T. H. et al. Appl. Phys. Lett. v. 64, (1994).
Magnetoresistive effect…
where R(H) and R(0) – resistance at certain
temperature with and without magnetic field;
Re
sis
tiv
ity
(Ω
*cm
)
Temperature (K)
Applications: • - Colossal Magnetoresistance Sensor (Hewlett-Packart ) for Ln1-yMyXO3; •- sensors and detectors of magnetic field sensitivity ~ 1 mkOe (firm NVE CBMP); •- detectors of magnetic field and current [Solid State Phenomena, v. 154, (2009)]; • - Magnetoresistive sensors (firm Honeywell); • - nonvolatile storage device (firm Motorola ).
Introduction Objectives Experimental
procedure
Results 6
Main aim of our work:
• Investigate the influence of chemical composition on: the changes of crystal structure and the parameters of
unit cell of perovskites; transport properties of manganites; of temperature factor on: the crystal and magnetic structures of double
perovskites;
• Learn to work with software (PowderCell and FullProf) for refinement of X-ray and neutron patterns.
Introduction Objectives Experimental
procedure
Results 7
• X-ray diffraction method at conventional diffractometer – information about phase composition and crystal structures.
• Neutron time-of-flight method (TOF-method) at High Resolution Fourier Diffractometer (HRFD), at nuclear reactor IBR-2M [1] (Dubna) – information about evolution of crystal and magnetic structures in a broad temperature range (20 – 470 K).
• Resistance and magnetoresistance were measured by four–probe method at magnetic fields H= 0 and 5 kOe, in temperature range from 77 to 400 К.
• Refinement of X-ray diffraction and neutron patterns were performed by PowderCell and FullProf software.
Experimental procedure :
[1] А.М. Balagurov // Neutron News, V. 16, №3, P.8, (2005).
Introduction Objectives Experimental
procedure
Results 8
Difference between X-ray and neutrons:
X-Ray Diffraction Neutron Diffraction
Electromagnetic wave Particle
X-ray photons interact with the
electron shells
Neutrons interact with the nucleus
No mass, spin 1, no magnetic dipole
moment
Mass, Spin 1/2, Magnetic dipole
moment
There is strong/line dependence of X-
ray scattering vs atomic number
There is not dependence of neutron
scattering vs atomic number
Magnetic structures cannot be investigated Magnetic structures can be investigated
Lower amounts of sample needed Large amounts of sample needed
Stronger absorption Lower absorption
Light elements hard to detect Light elements can be seen
High availability (lab instrument) Low availability (nuclear reactor)
Introduction Objectives Experimental
procedure
Results 9
a
c
b
Peak
shapes
X-ray or neutron powder Diffraction Pattern
10 20 30 40
2
PowderCell 2 .0
Atomic
distribution in
the unit cell
Peak relative
intensities
Symmetry
and size of
unit cell
Peak
positions
Crystallite size
and microstrain
FWHM
Introduction Objectives Experimental
procedure
Results 10
FullProf Suite: how does it work ?
Refinement of structure through
minimization of functional:
where yi - experimental meanings of intensities in i-th point,
yc,i – calculated meanings of intensities in i-th point,
wi – statistical weight of i-th point, as rule wi=1/yi (i=1,2,…n)
=( 1 2 … p), refinement parameters
Introduction Objectives Experimental
procedure
Results 11
Refinement Strategy
Introduction Objectives Experimental
procedure
Results
oi
cioi
py
yyR
Unweighted residual errors R (pattern)
2/1
2
2
oii
cioii
wpyw
yywR
weighted residual errors R (pattern)
oi
iy
W12/1
2exp
ii yw
PNR
)(
)()( )()(
oiy
ciyoiyR
i
hklhkl
B
RB: R-Bragg factor
Rexp: R expected
Where : "N" number of
observed patteren
" P" is the number of
parameters refined.
"W" weight factor.
exWP RR /GoFFor a good Results, GoF must have a value between
1 and 3
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La1-xCdxMnO3±δ (x=0 – 0.5)
La0.5Cd0.5MnO3 δ
CdMn2O4
1. Rhombohedral structure does not change in all concentration range; 2. x=0 – 0.2 – homogeneous; 3. x=0.3 – 0.5 – inhomogeneous
r(La3+)=1.36 Å
r(Cd2+)=1.34 Å
[1] R.D. Shannon / Acta Cryst. (1969). B25, 925
[1]
x=0.5
homogeneous
inhomogeneous
r(Mn3+)=0.645 Å
r(Mn4+)=0.53 Å
Introduction Objectives Experimental
procedure
Results
Rhom.
Rhom. +Tetrago.
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La1-xCdxMnO3±δ (x=0 – 0.4): Transport properties
The value of specific resistance decreases The value of magnetoresistance increases
as the concentration of Cd ions is increased from x=0 up to x=0.2
Introduction Objectives Experimental
procedure
Results
-2
0
2
4
6
8
10
12
14
16
0 100 200 300 400 500
MR
Temp . K
MR Vs Temp.
cd 0.1
cd0.15
Cd 0.2
cd 0.4
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Neutron Diffraction of Ba2FeMoO6
Introduction Objectives Experimental
procedure
Results
=>GOF 3.42
=>Bragg R-factor: 6.954
=>RF-factor: 10.91
=>Rwp: 10.6
=>Rexp:5.72
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Neutron Diffraction of Ba2FeMoO6
1. Near the point Tc=300 K of phase transition ferro-paramagnetic the type of crystal
structure is changed from cubic (sp. gr. Fm-3m) to tetragonal (sp. gr. I4/m)
2. The volume of unit cell as well as lattice parameters decreases as the temperature
of investigated sample is decreased.
)(
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12
12
1 TT
VV
VdT
dV
V p
αV=4.893*10-5 1/K
Introduction Objectives Experimental
procedure
Results 16
- Ba/Sr
- O
- Fe
- Mo
Magnetic structure of Ba2FeMoO6
T= 473 K
MFe=3.34 μB/f.un.
T= 20 K
MFe= 0 μB/f.un.
Introduction Objectives Experimental
procedure
Results 17
Conclusion_1:
• The refinement of X-ray patterns of solid solutions La1-
xCdxMnO3 δ (x=0 – 0.5) were performed by Rietveld method
using PowderCell and FullProf software.
• It was found out inhomogeneous of solid solutions La1-
xCdxMnO3 δ as the concentration of Cd exceeds x=0.2.
• The decreasing of specific resistance of La1-xCdxMnO3 δ
samples was explained by increasing of concentration of
Mn4+ ions due to substitution of La3+ by Cd2+ ions.
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Conclusion_2:
• The crystal and magnetic structures of Ba2FeMoO6 (T= 20;
310; 410 and 473 K) were refined by Rietveld method using
FullProf software.
• Near the point of phase transition (Tc=300 K) ferro-
paramagnetic the type of crystal structure of Ba2FeMoO6 is
changed from cubic (sp. gr. Fm-3m) to tetragonal (sp. gr.
I4/m).
• The volume of unit cell as well as lattice parameters
decreases as the temperature of Ba2FeMoO6 sample is
decreased
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Acknowledgment
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Thank you
Questions ?
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