1. STUDY OF THE INTERPLAY BETWEEN SPIN, CHARGE AND LATTICE IN MULTIFERROIC OXIDES RMn2O5 (R= Nd, Pr)
C. Doubrovsky1, F. Bouquet1, C. Pasquier1, P. Senzier1
M. Greenblatt3, S. Petit2, G. Andre2, F. Damay2, P. Foury1
phD director, Pascale Foury
1 Laboratoire de Physique des Solides (LPS), Orsay, France
2Labortaoire Léon Brillouin (CEA-CNRS), CEA Saclay, France
3Wright – Rieman Laboratories, Rutgers University, New Jersey

2. I. 1 Multiferroics
Spintronic
Type I : Weakly coupled orders (BiFeO3) 4 states memory Type II : Strong coupling between orders leading to ferroelectricity (RMn2O5) Electrical writing/Magnetic reading
Issue : Microscopic origin of the magneto-electric coupling Dzyaloshinskii Moriya or Exchange interaction

3. I. 2 Origin of the magneto-electric coupling
Magnetostriction effect
Non colinear : Dzyaloshinskii-Moriya interaction
O2- ligands shifts
Colinear : Exchange interaction
Mn3+ ions shifts P
Mn4+
Mn3+
R3+
S-W Cheong et al. Nature (2007)

4. J couplings in RMn2O5 (ab) plane– Loops of 5 Mn spins –
Magnetic superexchange interactions Ji = 3,5 are shown by double sided arrows.
P G Radaelli et al. J. P Condens. Matter (2008)
(ab) plane– Loops of 5 Mn spins –
J3 Mn3+/Mn4+ J4 Mn3+/Mn4+ through O2- J5 Mn3+/Mn3+
Along c – Mn4+ chains –
J1 through R3+ J2 through Mn3+

5. Gal case R = Y, Tb, Ho, Er, Tm  3 to 4 transitions (<50K)
I. 3 Rare earth influence in RMn2O5 
Gal case R = Y, Tb, Ho, Er, Tm  3 to 4 transitions (<50K)
TbMn2O5
Noda et al. J. P. Condens. Matter (2008)
non magnetic R
R= Bi (½ 0 ½) CP - ferroelectric
R=La (00 ½) CP - not ferroelectric
Lighter Rare Earth ?

6. II.1 Thermodynamic Properties
Syntheses, Rutgers University
II.1 Thermodynamic Properties
Specific heat on a PrMn2O5 powder
LPS, PPMS Quantum design.
Transitions at 20K and 25K

7. II.2 Magnetic Properties
25K
132K
Curie Law:
θc = 132K
C ~ emu.K.g-1.Oe-1  3,5 µB
(<µeff >= <µMn4+ + µMn3+ + µPr3+ > = 4,1 µB )
TN1 TC
Susceptibility of a PrMn2O5 powder
(SQUID, Rowan University, NJ)
25K transition AFM
20K transition not visible (small rearangement of the magnetic moment)

8. II.3 Dielectric Properties
Cp (pF)
T(K)
Dielectric constant of PrMn2O5 and TbMn2O5 powders (LPS, Orsay)
No ferroelectric transition
20K effect ? electromagnon as suggested in TbMn2O5?

9. III.1 Nuclear structure of PrMn2O5
Powder X-ray diffraction pattern taken at 10 and 70K of a polycristalline sample
Cristal beam line (SOLEIL)
Centrosymmetric Pbam structure confirmed
No structural variation (> 10-3) between 50 & 10K
 No significant magneto-striction effect

10. III.2 Magnetic structure of PrMn2O5
Magnetic spectra of PrMn2O5 powder, recorderd by elastic neutron diffraction (G4.1, Orphée LLB)
Integrated Intensity of the 2 sets of satelites peaks
2nd - order commensurate magnetic transitions at :
25K : q1 (1/2 00)
20K : q2 (001/2) Origin : Another PrMn2O5 phase?

11. III.2 Magnetic structure of PrMn2O5
TbMn2O5 P
q (1/2 01/4)
Pr3+
Mn4+
Mn3+
O2- b a
25K - q1 (1/2 00)
G. R. Blake, Physical Review B (2005)
Similar to TbMn2O5 and other RMn2O5
All magnetic atoms play part in the magnetic structure

12. TbMn2O5
Perspectives
Mesure and Modelisation of spinwaves  J coupling values in PrMn2O5 & TbMn2O5 (Inelastic neutron diffraction)
Understanding the low –T transition

13. Thank you for your attention

14. Interplay between spin, charge and lattice in multiferroics RMn2O5
I. Magnetoelectric coupling
Multiferroics
Origin of the magnetoelectric coupling
Rare earth influency in RMn2O5
II. PrMn2O5caracterisation
Synthesis of RMn2O5
Properties of PrMn2O5
III. Nuclear and magnetic structures of PrMn2O5
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15. In the ‘proper’ ferroelectrics, structural instability towards the polar state, associated with the electronic pairing, is the main driving force of the transition.
On the other hand, if polarization is only a part of a more complex lattice distortion or if it appears as an accidental by-product of some other ordering, the ferroelectricity is called ‘improper’

17. Mn (metal basis) washed in dilute HCl, dissolved in HNO3
Solid State Chemistry
600°C
1100°C O2
Pr6O Mn PrMn2O5
Mn (metal basis) washed in dilute HCl, dissolved in HNO3
XR- Results
Ref. : H. Satoh, S. Suzuki, K. Yamamoto, N Kamegashira, Phase Stabilities of LnMn2O5 (Ln = rare earth), Alloys and Compounds (1995)
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18. Susceptibility PrMn2O5 Electrolysis a//H b//H c//H 1 mm

19. TbMn2O5 CM magnetic structure
Plan (ab)
Along c direction
Mn3+
Mn4+
Mn3+ b
O2-
Mn4+
Tb3+ a
Colinear moments on a same site, with quite strange directions. Tb moment shave zero value when it is between AF ordered Mn layers.
q (1/2 01/4)

20. Other magnetic Structure of RMn2O5
TbMn2O5 b a
Magnetic frustration along b
Loops of 5 spins :
AFM order cannot be estblished
AFM along a

21. Reversible flipping of electric polarization in TbMn2O5