C. Doubrovsky 1, F. Bouquet 1, C. Pasquier 1, P. Senzier 1 M. Greenblatt 3, S. Petit 2, G. Andre 2,...

C. Doubrovsky1, F. Bouquet1, C. Pasquier1, P. Senzier1

M. Greenblatt3, S. Petit2, G. Andre2, F. Damay2, P. Foury1

1 Laboratoire de Physique des Solides (LPS), Orsay, France2Labortaoire Léon Brillouin (CEA-CNRS), CEA Saclay, France3Wright – Rieman Laboratories, Rutgers University, New Jersey

phD director, Pascale Foury

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. 1 Multiferroics

1/11

Spintronic

I. 2 Origin of the magneto-electric coupling

Non colinear : Dzyaloshinskii-Moriya interaction

O2- ligands shifts

Colinear : Exchange interaction

Mn3+ ions shifts

P

Mn4+

Mn3+

R3+

D S Sij i j

2/11

Magnetostriction effect

S-W Cheong et al. Nature (2007)

3/11

(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+

J couplings in RMn2O5

Magnetic superexchange interactions Ji = 3,5 are shown by double sided arrows.

P G Radaelli et al. J. P Condens. Matter (2008)

I. 3 Rare earth influence in RMn2O5

Gal case R = Y, Tb, Ho, Er, Tm 3 to 4 transitions (<50K)

Lighter Rare Earth ?

non magnetic R R= Bi (½ 0 ½) CP - ferroelectricR=La (00 ½) CP - not ferroelectric

1 1;0;2 4

q

1 1;0;2 4

q zx

1 1;0;2 4

q zx

4/11

TbMn2O5

Noda et al. J. P. Condens. Matter (2008)

Specific heat on a PrMn2O5 powder

LPS, PPMS Quantum design.

II.1 Thermodynamic Properties

5/11

Transitions at 20K and 25K

Syntheses, Rutgers University

6/11

25K

II.2 Magnetic Properties

Susceptibility of a PrMn2O5 powder

(SQUID, Rowan University, NJ)

Curie Law: θc = 132KC ~1.46 10-2 emu.K.g-1.Oe-1 3,5 µB (<µeff >= <µMn4+ + µMn3+ + µPr3+ > = 4,1 µB )

25K transition AFM20K transition not visible (small rearangement of the magnetic moment)

TN1

132K

TC

Cp (

pF

)

II.3 Dielectric Properties

7/11

Dielectric constant of PrMn2O5 and TbMn2O5 powders (LPS, Orsay)

No ferroelectric transition20K effect ? electromagnon as suggested in TbMn2O5?

T(K)

III.1 Nuclear structure of PrMn2O5

Powder X-ray diffraction pattern taken at 10 and 70K of a polycristalline sample Cristal beam line (SOLEIL)

8/11

Centrosymmetric Pbam structure confirmedNo structural variation (> 10-3) between 50 & 10K

No significant magneto-striction effect

Magnetic spectra of PrMn2O5 powder,

recorderd by elastic neutron diffraction (G4.1, Orphée LLB)

III.2 Magnetic structure of PrMn2O5

9/11

λ= 2,4226 A

2nd - order commensurate magnetic transitions at :• 25K : q1 (1/2 00)• 20K : q2 (001/2) Origin : Another PrMn2O5 phase?

Integrated Intensity of the 2 sets of satelites peaks

10/11

III.2 Magnetic structure of PrMn2O5

• Similar to TbMn2O5 and other RMn2O5• All magnetic atoms play part in the magnetic structure

TbMn2O5

P

q (1/2 01/4)25K - q1 (1/2 00)

PrMn2O5

Pr3+

Mn4+

Mn3+

O2-

b

a

G. R. Blake, Physical Review B (2005)

Perspectives Mesure and Modelisation of spinwaves J

coupling values in PrMn2O5 & TbMn2O5 (Inelastic neutron diffraction)

Understanding the low –T transition

11/11

TbMn2O

5

Thank you for your attention

Interplay between spin, charge and lattice in multiferroics RMn2O5

I. Magnetoelectric coupling1.Multiferroics2.Origin of the magnetoelectric coupling 3.Rare earth influency in RMn2O5

II. PrMn2O5caracterisation

1.Synthesis of RMn2O5

2.Properties of PrMn2O5

III. Nuclear and magnetic structures of PrMn2O5

2/9

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’

16

Solid State Chemistry

Ref. : H. Satoh, S. Suzuki, K. Yamamoto, N Kamegashira, Phase Stabilities of LnMn2O5 (Ln = rare earth), Alloys and Compounds (1995)

600°C 1100°C O2

Pr6O11 + 12Mn 6 PrMn2O5

Mn (metal basis) washed in dilute HCl, dissolved in HNO3

XR- Results

6/12

Susceptibility

18

PrMn2O5 Electrolysis

1 mm

a//H

b//H

c//H

0 10 20 30 40 50

Plan (ab) Along c direction

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)

b

a

TbMn2O5 CM magnetic structure

O2-

Mn3+

Mn4+

Tb3+

Mn4+

Mn3+

Other magnetic Structure of RMn2O5

Magnetic frustration

along b

TbMn2O5

b

a

Loops of 5 spins :

AFM order cannot be estblished

AFM along a

Reversible flipping of electric polarization in TbMn2O5

21