Post on 13-Jan-2016
description
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
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• 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’
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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
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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
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