thin film laser ablation group in tifrpratap/laser ablation.pdf · ayyub (ferroelectrics and...
TRANSCRIPT
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Thin Film Laser Ablation Group in TIFR
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External Users (in the last 1 year)
1. Sundar Manoharan, IIT Kanpur2. R. Kuberkar, Sourashtra University
3. Neeraj Khare, NPL Delhi4. Indranil Das, SINP Kolkata
5. Prabhat Mandal, SINP Kolkata6. S. M. Hussain, S. V. University, Tirupati
Internal Users
1. Pratap Raychaudhuri (CMR and HTSC films)2. V. Palkar (Ferroelectric and magnetoferroelectric materials)
3. P. Ayyub (Ferroelectrics and antiferroelectrics)
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Transport and magnetic properties of the new electron doped manganite La1-xCexMnO3
Pratap Raychaudhuri
Tata Institute of Fundamental Research Mumbai.
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Plan of the talk
• Why electron doped manganites?The symmetry between electron and hole doped manganites
• Is La1-x
CexMnO
3 electron doped?
X-ray absorption
• Transport and magnetic properties of La1-x
CexMnO
3
Phase diagram for x≤0.3
• Spectroscopy using ferromagnetic tunnel junctions of electron and hole doped manganites
The band structure jigsaw
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Collaborators:
C. MitraUniversity of Cambridge, UK
S. Wirth
MPI Dresden, Germany
C. Hu, S. Csiszar and L.H. Tjeng and C. T. Chen Universitat zu Koln, Germany
R. PintoTIFR, Mumbai
P. MandalSaha Institute of Nuclear Physics, Calcutta, India.
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LaMnO3Αntiferromagnetic charge transfer insulator
Mn: Mn3+ valence state
La(3+)1-xCa(2+) xMnO3
Mn: Mn3+/Mn4+
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La(3+)MnO3
Electron HoleLa(3+)
1-xCe(4+) xMnO3 La(3+)1-xCa(2+) xMnO3
Mn4+Mn3+Mn2+
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Inherent symmetry between electron and hole dopingMn2+/Mn3+ instead of Mn3+/Mn4+
Zener Double exchange
Jahn-Teller effect
Mn2+ Mn3+
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The layered perovskite compound R2+x
A1-x
Mn2O
7
R=rare-earth A=bivalent cationParent material: La
2CaMn
2O
7
Hole doping:La
2-xCa
1+xMn
2O
7
Electron doping:(La,Y)
2.3Ca
0.7Mn
2O
7
Tc~160K
Ms~4.33µ
B/Mn ion P.Raychaudhuri et al., JPCM 10, L191
(1998)
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The perovskite compound La0.7
Ce0.3
MnO3
Ce: Ce4+ Mn: Mn2+/Mn3+
P. Mandal and S. Das, PRB 56, 15073 (1997)
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Epitaxial thin film of La0.7
Ce0.3
MnO3
on LaAlO3 through Pulsed Laser Deposition
P. Raychaudhuri et al., JAP 86, 5718 (1999)
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Rietveld refinement showed the existence of >20% unreacted CeO2 in bulk
X-ray diffraction pattern
CeO2
bulk
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XRD of epitaxial and polycrystalline film grown through Pulsed Laser Deposition
Epitaxial film on LaAlO3
Polycrystalline film on YSZ
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Pulsed Laser deposition
Mn2+ is a large ion which does not get incorporated in the lattice easily• Fast process (20-30ns)• High energy (0.1GW)
Pulsed laser deposition can be used to stabilise compounds which are not easily synthesized in bulk.
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Metal-insulator transition and morphology
100 mTorr
200 mTorr
400 mTorr
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Is La0.7Ce0.3MnO3 an electron doped manganite?
• Is Ce is Ce4+ state?• Oxygen stoichiometry? (overoxygenation≡hole doping)
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X-ray absorption spectroscopy
Mn2+
Mn3+
Mn4+
Ce3+
Ce4+
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La1-x
CexMnO
3 (0≤x≤0.3)
x<0.15: Ferromagnetic insulator x≥0.15: Ferromagnetic metal
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Magnetic Properties at Low Doping
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Which kind of Ferromagnet ?
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Conventional probe: Meservey Tedrow technique
Fabricating tunnel junction between a ferromagnet and a superconductor with low spin orbit coupling
Al
Ferromagnetic tunnel junction
- Juliere's Formula
MR<0 if P1 and P
2 have same sign
MR>0 if P1 and P
2 have different sign
MR��2P1 P2
1�P1 P2
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(Ferromagnetic) Tunnel junction between hole doped and electron doped manganites
Both electrode ferromagnetic below 250 K.La0.7Ca0.3MnO3 (Majority spin carrier) is used as a spin analyser.
C. Mitra, P. Raychaudhuri et al., Phys. Rev. Lett. (in press)
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Zero magnetic field
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Negative MR at low bias
Positive MR at high bias
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Magnetic field 20kOe
T<<Tc
Positive MR (all bias)
The ground state of La0.7Ce0.3MnO3 has a minority spin character
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Speculation: Band diagram
4.33 electrons in the 3d shell
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Band diagram
Low T
High T??
cf
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Conclusion
(La,Ce)MnO3 is a electron doped manganite with negative spin polarisation.
Future Directions
The symmetry between electron and hole doping: Why this symmetry?
Higher electron doping: Charge ordering at x≈≈≈≈0.5??
Other electron doped manganites: (La,Sn)MnO3
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This presentation was made solely using the freefreefreefreefreefreefreefreefreefree software
StarOffice 5.2.