1. AMnGe2O6 (A = Ca or Sr) : effect on the divalent cation in the pyroxene structure : how to induce multiferroicity?
Lei Ding, Céline Darie , Claire V. Colin , Julien Robert, Frédéric Gay, Pierre Bordet
INSTITUT NEEL, CNRS,
Univ Grenoble Alpes F Grenoble, France
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2. What does Multiferroic mean?
Two « ferroic » properties are present in the material.
TYPE I (ex: BiFeO3)
TYPE II (ex: TbMnO3)
Different origins for Magnetism & Ferroelectricity.
Low coupling between them.
Magnetism induces Ferroelectricity
Strong coupling between them
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3. GDRMEETIC_Bordeaux_28-31 Mars 2017
What is pyroxene compound?
Pyroxenes are one of the most common minerals in the earth crust.
Known for a long time :
First publication: 1900!: “On pyroxene from Latium” Zambomni
Zeitschrift Fur Krystallographie und Mineralogie
And famous : more than publications (mostly in the mineralogical and geological domains…)
Pyroxenes and Magnetism : 1996 ….
Pyroxenes
and Multiferroism : 2007
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4. GDRMEETIC_Bordeaux_28-31 Mars 2017
What is pyroxene compound?
Edge-sharing MO6 octahedra chain
General Formula: AMX2O6
A = alkali metal monovalent cation: Na+, Li+
or alkaline earth divalent cation: Ca2+
M = Transition metal cation:
M3+: Ti3(d1), V3+(d2), Cr3+(d3), Mn3+(d4), Fe3+(d5)
M2+: Mn2+(d5), Fe2+(d6), Co2+ (d7), Ni2+ (d8) …
X = Si4+ (natural) or Ge4+ (synthetic)
Clinopyroxene: monoclinic C2/c, P21/c
Z=4, a ≈ 10 Å, b≈ 9 Å, c≈ 5.4Å,  ≈105°
Intrachain M-M distance: 3.1Å
Interchain M-M distance: 5.9Å
Corner-sharing XO4 tetrahedra chain A
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5. What is pyroxene compound?
Low-dimensional magnetic subsystem with M-O-M angle close to 90° :
Competition between different contribution to intrachain exchange interaction (direct and SE)
Magnetic coupling depends on d-orbital occupancy O2 O1
General topology of exchange interaction is triangular-like (SSE) : it may be frustrated J J1 J2
Non-trivial structural/magnetic properties
Streltsov and Khomskii , PRB, 2008, 77,
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6. GDRMEETIC_Bordeaux_28-31 Mars 2017
Non trivial magnetic structures
Depending of the nature of A, M and X : A+
M3+
X4+
FM long range order: NaCrGe2O6
Commensurate AFM: NaCrSi2O6
Incommensurate AFM NaFeGe/Si2O6
Linear magnetoelectric effect : LiFeGe/Si2O6
Multiferrelectric effect : NaFeSi2O6
X4+
A2+
M2+
Less studies on 2:2
pyroxenes
Redhammer et al. Z. Kristallogr., 2013, 228, 140
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7. Why divalent-TM pyroxenes?
Known pyroxenes containing divalent cations A2+M2+T2O6 (T=Ge,Si)
Comp. SG
Propag. Vector
MSG
Magnetic structure: Intrachain
Inter-chain
Phy. Property
Ref.
CuMgSi2O6
P21/c -
Paramagnet
Ding, Mineral.Mag. 2015
CaCuGe2O6
Spin-singlet~40K
Behruzi, Z.Kristallogr., 1986
CaNiGe2O6
C2/c
(1,0,0)
C2’/c’ FM
AFM
TN=18K
Redhammer, JSSC, 2008
CaNiSi2O6
TN=22K
Durand., JSSC, 1996
CaCoGe2O6
JSSC, 2008
CaCoSi2O6
TN=10K
Durand, JSSC, 1996
CaFeGe2O6
TN=43K
Redhammer, Z.Kristallogr, 2013
CaFeSi2O6
TN=35K
CaMnGe2O6
(0,0,0)
C2’/c
TN=12K
CaMnSi2O6 ?
Nestola, Am. Mineral. 2010
SrMnGe2O6
Linear ME
Possible magnetic
frustration
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8. JMC15_MP3_Bordeaux_26 Aout 2016
AMn2+X2O6 J J1 J2
Edge-sharing MO6 octahedra chain
Intrachain : AFM
Interchain : FM
Corner-sharing XO4 tetrahedra chain
How to play with the interchain interaction ?
chemical substitution
X site : Ge4+ vs Si4+ and A site : Ca2+ vs Sr2+
CaMnGe2O6 / CaMnSi2O6 / SrMnGe2O6
JMC15_MP3_Bordeaux_26 Aout 2016

9. GDRMEETIC_Bordeaux_28-31 Mars 2017
CaMnGe2O6
Synthesis : SSR with intermediate regrinding 1200°C 96h
Impurity Ca3Mn2Ge3O (1) wt%
XRD : C2/c a= (3); b=9.1756(3); c=5.4714(2); b= (2)
NPD
RT NPD, 1.28Å,
TN=15K
~45K: Mn3O4 ferrimagnetic Impurity
Lei Ding et al PRB 2016,
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10. GDRMEETIC_Bordeaux_28-31 Mars 2017
CaMnGe2O6
Determination of the magnetic structure
Linear magneto-electric effect
Pyroelectric current measurement: ME annealing EH (pressed pellet)
Lei Ding et al PRB 2016,
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11. GDRMEETIC_Bordeaux_28-31 Mars 2017
CaMnSi2O6
Synthesis : solid state reaction under 5GPa, 1200°С, 3h.
XRD : C2/c a=9.9209(2); b=9.1370(2);
c=5.2747(1); b= (3)
NPD : magnetic structure
Linear magneto-electric effect
TN=12K
(no Mn3O4 impurity)
Pyroelectric current measurement: ME annealing EH (pressed pellet)
k=(0,0,0)
Space group C2‘/c
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12. GDRMEETIC_Bordeaux_28-31 Mars 2017
SrMnGe2O6
Synthesis : SSR with intermediate regrinding 1100°C 96h
XRD : C2/c a= (6); b=9.4204(5); c=5.5093(3); b= (2)
NPD : magnetic structure
TN=4.5K
4.5K
Lei Ding et al J. Mater. Chem C, 2016, 4, 4236
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13. GDRMEETIC_Bordeaux_28-31 Mars 2017
SrMnGe2O6
Cycloidal structure => multiferroicity of type II
Lei Ding et al J. Mater. Chem C, 2016, 4, 4236
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14. GDRMEETIC_Bordeaux_28-31 Mars 2017
SrMnGe2O6 : multiferroic of type II
Spontaneous electric polarization
appears at TN
Strong anomalous magnetostrictive
effect at TN
Lei Ding et al J. Mater. Chem C, 2016, 4, 4236
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15. GDRMEETIC_Bordeaux_28-31 Mars 2017
AMn2+X2O6: effect of A and X?
CaMnGe2O6
Property
Linear magneto-electric
CaMnSi2O6
SrMnGe2O6
Linear magneto-electric
Multiferroic Type II
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16. Thank you for your attention!
HP-HT
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17. GDRMEETIC_Bordeaux_28-31 Mars 2017