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

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

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)

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+

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 ?

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

II.2 Magnetic Properties 25K 132K Curie Law: θc = 132K C ~1.46 10-2 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)

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?

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

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?

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

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

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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 2/9

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’

Mn (metal basis) washed in dilute HCl, dissolved in HNO3 Solid State Chemistry 600°C 1100°C O2 Pr6O11 + 12Mn 6 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) 6/12

Susceptibility PrMn2O5 Electrolysis a//H b//H c//H 1 mm 0 10 20 30 40 50

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)

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

Reversible flipping of electric polarization in TbMn2O5