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
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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).
• 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.