Title: Coexistence of magnetism and ferroelectricity in Pr,CaMnO3 near half doping: a first principles inve
1Coexistence of magnetism and ferroelectricity in
(Pr,Ca)MnO3 near half doping a first principles
investigation G. Colizzi, A. Filippetti and
V. Fiorentini CNR-INFM SLACS and Department of
Physics University of Cagliari
FOxE - Functional Oxides for Electronics Villa
Angelina, Massa Lubrense, Sorrento (NA)? 25-27
Marzo 2009
2PCMO phase diagram
After B.Raveau et al. j. mater. Chem. 2001, 11
29-36
Our Regions of interest
3A debated question CE-ordering or Zener
Polaron?
CE-ordering
Zener-polaron
After A. Doud-Aladine et al. PRL. 89 , 2002
After A. Trokiner et al. PRB. 74 , 2006
4An even more exotic phenomenology is predicted
!!!!
Mn3
Mn4
0.4 doping ZP -ord.
0.5 dopingCE-ordering
0.45 dopingFE !!!
D. Efremov et al. Nat. Mat. 3, 853 (2004)?
5Pr0.5Ca0.nO3 crystal(high-T)?
- Computational details
- Large supercell 80 atoms(necessary for
simulating AF-CE )? - Structural and magnetic point group C2h
(centrosymmetric) - Ab initio density functional theory (DFT)? VASP
code and GGAU8 (Anisimov et al. PRB 1997)
Polarization within the Berry phase formalism - All atoms relaxed !!!!
- Anisimov results well reproduced with some
exceptionInsulating, OO and (small) CO ok but
the Magn.-Mom.disproportion of Mn present only
after relaxation otherwise all Mn atoms Are
equivalent !
- Orthorhombic crystal space group Pbnm (Z. Jirak
et al. 1985)20 atoms primitive cell - Rotated and tilted almost undistorted MnO6 oxygen
octahedra
- Zener polarons never realized together with AF-CE
magnetic phase even when starting from a inizial
structure made of Mn-O-Mn ZP trimers
6Pbnm structure relaxed Ferroelectric!!!
- Atoms which are struct.-elect. magn.-ly
equivalent show similar displacements but ...
because of the OO in Mn atoms no exactly equal
!!! gt A small polarization appears!!! -
- Because of the Orbital Ordering The Polarization
is not exactly parallel to a crystal axis (b in
our picture) as predicted by Efremov et al. - This polarization grows dramatically to 0.77
mC/m2 if just a system with a slightly less
omogeneous Ca and Pr distribution is considered
Ptot 0.89mC/m2 (Pion0.55mC/m2,Pel0.34mC/m2)
7Conclusions
- According to DFT Pr0.5Ca0.5MnO3 Pbnm crystal
8Ackowledgments
- Special thanks to Pietro Delugas now
- at IMM-CNR Catania for all his precious
suggestion - Alessandra Lehmann and her group who introduced
us to PCMO physics - All the organizers of FoxE
- All of you for your attention
FOxE - Functional Oxides for Electronics Villa
Angelina, Massa Lubrense, Sorrento (NA)? 25-27
Marzo 2009
9Pbnm structure relaxed
- Atoms which are struct.-elect. magn.-ly
equivalent show similar displacements - Intrachain O's mainly move parallel to the
Mn-O-Mn bond approaching their Mn-corner atom - O-Mn-O AF trimers are formed strong Mn-O
hybrydization and Mn atoms deeply hybridized!!!! -
- Interchain O's move less and mainly
perpendicularly - to the Mn-O-Mn bond
- Charge-Ordering(CO) all Mn's have very similar
electric charge, ?q0.05e- more relevant the
difference for Mn's magnetic moment ?m0.30uB a
similar CO also for O's where ?q0.03e- and also
played by the - MnO6 octahedra of two types distorted(side-chain
centred) and undistorted (corner-chain centred) - Ab initio density functional theory (DFT)? VASP
code and GGAU8 (Anisimov et al. PRB 1997)? - All atoms relaxed !!!!
- Anisimov results well reproduced with some
exceptionInsulating, OO and (small) CO ok but
the Magn.-Mom.disproportion of Mn present only
after relaxation otherwise all Mn atoms Are
equivalent !