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

1

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

3

δ=0

0<δ<0.15

0.15≤ δ

4

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

4

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

6

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

12

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.

13

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

14

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

15

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.

)(

11

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.

18

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

19

Acknowledgment

20

Thank you

Questions ?

21