LOCAL PROBE STUDIES IN MANGANITES AND COMPLEX OXIDES
V.S. Amaral1, A.M.L. Lopes2, J.P. Araújo3, P.B. Tavares4, T.M. Mendonça3,5, J. S. Amaral1, J.N. Gonçalves1,5, J.G. Correia5,6 and IS390 Collaboration
1Dep. Física and CICECO, Univ. Aveiro, 3810-193 Aveiro, Portugal;2CFNUL, Univ. Lisboa, 1649-003 Lisboa, Portugal; 3Dep. Física and IFIMUP, Univ. Porto, 4169-007 Porto, Portugal;4CQ-VR, UTAD, 5001-801 Vila Real, Portugal; 5CERN EP, CH 1211 Geneve 23, Switzerland; 6ITN, E.N. 10, P-2685 Sacavém, Portugal
OUTLINEManganites and intrinsic complexity
Charge-ordering scenarios, phase separationMultiferroic systems
Local Probe StudiesHyperfine technique: Perturbed Angular Correlations
Probing electric fields in Pr1-xCaxMnO3 system
Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3
Multiferroics: RMnO3
Other oxide systems
Perspectives
Manganites
Electron doping (charge
and orbital)
Structure
Magnetic Interactions
AMnO3 ( A=La, Pr, Nd &Ca, Sr ...)base structure perovkite
Mixed valence: Mn3+ : Mn4+
Doping with divalent ions
(R-D)MnO3
Mn3+ 3d4
La3+
O2-
eg
t2g
crystal field splitting
JT effect
If only Mn3+ collective JT distortion
O
Introduction to Manganites
Pr1-xCaxMnO3
Magnetic - Electric Phase Diagram C
O/O
O s
igna
ture
s Small Ionic radii
Pr3+ =1.30 Å, Ca2+ =1.34 Å
-Orthorhombic structure for all x
Small overlap between Mn & O orbitals
-Insulator for all x
Charge Order is stabilized over a broad
range of compositions
Introduction to Manganites
Mn3+/Mn4+ localization in a ordered way
Phase separation and complexityAtomic-scale coexistence
Renner et al, Nature 416, 518 (2002)Bi0.24Ca0.76MnO3
Charge contrast: occupied and unnocupied states
Clusters with CE type arrangement in the paramagnetic phase
Ma et al, Phys Rev. Lett
95, 237210 (2005)
(La,Pr)5/8Ca3/8MnO3
20x10 nm
OUTLINEManganites and intrinsic complexity
Charge-ordering scenarios, phase separationMultiferroic systems
Local Probe StudiesHyperfine technique: Perturbed Angular Correlations
Probing electric fields in Pr1-xCaxMnO3 system
Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3
Multiferroics: RMnO3
Other oxide systems
Perspectives
Multiferroic materials•Inversion symmetry breaking (charge-orbital related) •Dislocated spin density waves•Magneto-electric coupling
Nature Materials 3, 164, (2004)
20
22
24
26
0 2 4 6 8
-40
-20
0
20
40
0 1000 2000 3000 4000
-40
-20
0
20
40
0
1
2
(b)
(c)
(a)
3 K
28 K
1 kHz
+
- -
+
-Pn
++
- -
+
-Pn
+
+Ha
bc
+ +
--Pn
-
++H
a
bc
+ +
--Pn
-
+P (
nC
/cm
2 ) 28 K
3 K
H (T)
P (
nC
/cm
2 )
Time (sec)
H (
T)
Tb/YMn2O5 Nature, 429, 392 (2004)
Magnetic field induces a sign reversal of the electric polarization
Multiferroic manganites
Van Aken , thesis univ. Groningen
Perovskite phasesoctahedra
Hexagonal phaseTrigonal bipyramid
AMnO3
Ferroelectricity due to Charge Ordering in Pr1-xCaxMnO3
New paradigm for ferroelectrics, but it has been hard to prove experimentally that electric polarization exists in CO Pr1-xCaxMnO3
(due to finite conductivity)
New scenario for the Charge Ordered State
Theoretical work predicts the possibility of local electric dipole moments in CO manganites
Ferroelectricity
Inversion symmetry is broken
=
Site centred CO Bond centred CO
+
D.Efremov et al, Nature Materials, 3,853 (2004)J. Van den Brink, D.I. Khomskii, J. Phys. Cond. Matt 20, 434217 (2008)
Charge ordered manganites
OUTLINEManganites and intrinsic complexity
Charge-ordering scenarios, phase separationMultiferroic systems
Local Probe StudiesHyperfine technique: Perturbed Angular Correlations
Probing electric fields in Pr1-xCaxMnO3 system
Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3
Multiferroics: RMnO3
Other oxide systems
Perspectives
Two-Photon PERTURBED ANGULAR CORRELATIONTwo-Photon PERTURBED ANGULAR CORRELATION
Hyperfine splitting Electric field gradient / Magnetic hyperfine field
Vzz - EFG principal component
- Asymmetry parameter
Bhf - Magnetic hyperfine field
|Ii, mi ⟩ , Q
L2 |I, m ⟩
|If, mf ⟩
1
2
L1
E
Ei
E
Ef
Local Probe Studies / Technique
Time dependence gives access to splitting of hyperfine levels
Probe nucleus:
Q – quadrupolar moment
- magnetic moment
Two-Photon PERTURBED ANGULAR CORRELATIONTwo-Photon PERTURBED ANGULAR CORRELATION
Samples implanted with radioactive 111mCd @ ISOLDE/CERN
E=60 keV, Dose < 1012 at/cm2
111mCd: I=5/2 and t1/2= 85 ns
Q=0.83 b and =-0.766 n
Samples annealed @ T=700 ºC in air
CdCd @ Pr/CaPr/Ca site
Local Probe Studies / Technique
PROPOSAL TO THE ISOLDE COMMITTEE – INTC/P132 Add1
IS390-Studies of Colossal Magnetoresistive Oxideswith Radioactive Isotopes
Aveiro1, Dublin2, Leuven3, Lisboa4, Moscow5, Orsay6, Porto7, Sacavém8,
Stuttgart9, Tokyo10, Tsukuba11 Vila Real12 and the ISOLDE/CERN13 Collaboration
Spokesman: V. S. Amaral
Contact person: J.G. Correia
E. Alves8, T. Agne13, J.S. Amaral1, V.S. Amaral1, J.P. Araújo7, J. M. D. Coey2, N. A. Babushkina5, J.G. Correia8,13, H.-U. Habermeier9, A. L.
Lopes1, A.A.Lourenço1, J.G. Marques4,8, T. M. Mendonça7, M. S. Reis1, E. Rita8, J.C. Soares4, J.B. Sousa7, R. Suryanarayanan6, P.B. Tavares12, Y.
Tokura10,11, Y. Tomioka11, A. Vantomme3, J.M. Vieira1 and U. Wahl8.
OUTLINEManganites and intrinsic complexity
Charge-ordering scenarios, phase separationMultiferroic systems
Local Probe StudiesHyperfine technique: Perturbed Angular Correlations
Probing electric fields in Pr1-xCaxMnO3 system
Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3
Multiferroics: RMnO3
Other oxide systems
Perspectives
x=0.25 (NO CO) @ ≠ Temperature ≠ Ca (x) content @ RT
EXPERIMENTAL RESULTS
Pr1-xCaxMnO3 PAC Anisotropy Functions
Local Probe Studies / Pr1-xCaxMnO3 system
@ RT @ 896K
Vzz increases with decreasing T due to atomic vibrations (rms displacements)
High temperature linear slope ~ -1.5(1)10-4 K-1
Temperature dependence for samples outside CO region
EFG principal component Vzz
Local Probe Studies / Pr1-xCaxMnO3 system
Samples within CO region
Anomalous Vzz(T) dependence
approaching CO transition
Charge order driven by the softening of a vibration mode?
Softening of vibration modes?
Same high temperature linear slope ~ -1.5(2)10-4 K-1
Local Probe Studies / Pr1-xCaxMnO3 system
TCO
CO region, Vzz vs Temperature
T*
Local Probe Studies / Pr1-xCaxMnO3 system
Sharp increase of Vzz @ T< TCO
Dropping @ T* (85 to 67 Vzz/Å-2 in 2K)
TCO
CO region, Vzz vs Temperature
T* TCO
T* TCO
T*
Local Probe Studies / Pr1-xCaxMnO3 system
Sharp increase of Vzz @ T< TCO
Dropping @ T*
EFG and magnetic susceptibility
Local Probe Studies / Pr1-xCaxMnO3 system
From NMR and PAC studies in Ferroelectrics
el20
zz βTχαPVVsZZ
Susceptibility Increase
LocalSpontaneous Polarization
TC
EFG sensitive to atomic vibrations and critical fluctuations
Local Probe Studies / Pr1-xCaxMnO3 system
compatible with first-order dielectric phase transition below Tco
Results Electric susceptibility / spontaneous polarization below TC
x=0.35 ->TEDO=206 K, x=0.4 ->TEDO=218 K,
x=0.85 -> TEDO=112 K
Local Probe Studies / Pr1-xCaxMnO3 system
A.M.L. Lopes et al., Phys. Rev. Lett. 100, 155702 (2008)
Piezoresponse Force Microscopy-hysteresis loop at room temperature:
The piezoelectric contrast points to the existence of a local polar state
Piezoelectric Force Microscopy in Pr1-xCaxMnO3 system
A. L. Kholkin, I.K. Bdikin, CICECO; Univ. Aveiro
Local Ferroelectric response in Pr0.6Ca0.4MnO3 single crystal
OUTLINEManganites and intrinsic complexity
Charge-ordering scenarios, phase separationMultiferroic systems
Local Probe StudiesHyperfine technique: Perturbed Angular Correlations
Probing electric fields in Pr1-xCaxMnO3 system
Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3
Multiferroics: RMnO3
Other oxide systems
Perspectives
LaMnOLaMnO3+3+
Orthorhombic (O’)
Strong JT distortion
Antiferromagnetic
Rhombohedric (R)
No collective JT distortion
Ferromagnetic
Mn3+/ Mn4+ MIX-VALENCE
Only Mn3+ collective JT distortion
Doping Mn3+1-2 / Mn4+
2 MIX-
VALENCE
(La3/(3+)Mn3/(3+ )
O3)
PAC anisotropy functions
@ RT
and Vzz as a function
of
Orth
orro
mb
ic O
rthorro
mb
ic
Rh
om
boh
ed
ricR
hom
boh
ed
ric
LaMnOLaMnO3+3+
LaMnOLaMnO3.123.12
Polarons ?Polarons ?
Polaron nature and evolution?
Polarons responsible for FM INSULATOR state?
Ferromagnetic Insulator state @ T<TC
Rhombohedric Orthorhombic phase transition ~ RT
Phase coexistence in a broad range of T
PAC anisotropy functions @ ≠ T O
rth
Rh
oO
rth
+R
ho31
8 K
19
7 K
Rho crystallographic phase (x-ray)
Orth crystallographic
Phase (x-ray)
MHF for T<TC (TC=145 K)
Coexistence of two local environments for all T
Macroscopic Rho + Orth
phase coexistence (x-ray)
% of u and d local environments
RhoOrt % Ort
High T X-rays do not see distorted phase Random distributed polaron clusters
Strong JT distortions in the Rho. Phase Polarons clusters start to form @ T*>776 K
R+Ox-ray
Smooth variation fu (and fd) Percolation
threshold
Percolation of the local environments
31%
Below percolation threshold distortions accommodate in a weakly JT distorted phase
and Vzz vs T
Lightly doped La-Ca manganite
The same physics?
R to O* transitions on cooling
Intermediate JT-orbital ordering transition to O structure
J. B. Goodenough, 2003
La0.95Ca0.05MnO3
100 200 300 400 500 600 700 800 900 100040
53
66
79
93
106
119
132
Vzz
(V
/Å2 )
T (K)
RO*O
100 200 300 400 500 600 700 800 900 1000
0
20
40
60
80
100
F1
, F2
(%
T (K)
RO*O
T>900K One fraction; low
T<900K Two fractions: high/low VzzChange ratio at T~750KOnly minoritary fraction sensitive to JT transition
T=900K R to O* transition
100 200 300 400 500 600 700 800 900 1000
0
20
40
60
80
100
F1
, F2 (%
T (K)
RO*O
La0.95Ca0.05MnO3
PAC very sensitive to charge distribution changes:Disproportionation?
OUTLINEManganites and intrinsic complexity
Charge-ordering scenarios, phase separationMultiferroic systems
Local Probe StudiesHyperfine technique: Perturbed Angular Correlations
Probing electric fields in Pr1-xCaxMnO3 system
Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3
Multiferroics: RMnO3
Other oxide systems
Perspectives
RMnO3 vs. R ionic radius
0.00
0.07
0.0
0.6
0.000.0
0.000.0
0.00 0.0
0.000.0
0.000.0
0 50 100 150
0.00400 800
0.0
Increasin
g io
nic rad
ius
LuMnO3
YMnO3
YbMnO3
Inten
sity
R(t)
(Mrad/s)
time (ns)
HoMnO3
ErMnO3
GdMnO3
EuMnO3
Single phase RMnO3 samples
(excepting LuMnO3 with traces of Lu2O3)Lu2O3
0.00
0.05
0.0
0 50 100 150 200 250
0.00
0 200 400 600 8000.0
1123K
0.0
0.7
0.00
973K
0.0
0.00
293K
573K
0.0
0.00
10K
R(t)
Time (ns)
Frequency (Mrad/s)
YMnO3 vs. Temperature
100
150
200
0 200 400 600 800 1000 1200
0.3
0.6
Temperature (K)
Mrad/s
ParamagneticFerroelectric
AFMFE
Paraelectric
Two EFG’s present in YMnO3 samples
EFG1
f1~70%w0~120 Mrad/s
EFG2
f2~30%w0~180 Mrad/sHexagonal structure
EuMnO3 vs. Temperature
0.00
0.06
0 50 100 150 200 2500.00
200 400 600 8000.00
293K
773K
968K
0.00
0.62
0.00
150K
573K 0.00
0.00
53K
0.00
0.00
30K
20K
0.00
0.00
0.00
0.00
15K
12K
Time (ns) Frequency (Mrad/s)
0.00
0.000.00
0.000.00
0.00
0.00
0.00
10K 0.00
R(t)
Two EFG’s present in EuMnO3 samples
EFG1
f1~35-40%w0~120 Mrad/s
EFG2
f2~60-65%w0~180 Mrad/s
Inversion of the main EFG below 20K
120
180
(Mrad/s)
0 200 400 600 800 10000.2
0.4
0.6
Temperature (K)
AFM Paramagnetic and Paraelectric
Orthorhombic structure
OUTLINEManganites and intrinsic complexity
Charge-ordering scenarios, phase separationMultiferroic systems
Local Probe StudiesHyperfine technique: Perturbed Angular Correlations
Probing electric fields in Pr1-xCaxMnO3 system
Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3
Multiferroics: RMnO3
Other oxide systems
Perspectives
AgCrO2 (111In probe): a new multiferroic
294.5K
48.6K
21.4K
19.2K
Ag2NiO2 and analogous: Orbital physics vs Charge Order
Like AgCrO2 111Ag and 111Cd/In probes for the 2 sites: more complete mapping of charge distributions
Valence(charge) changes in Ag and Ni avoiding Jahn-Teller distortion
CONCLUSIONS
- Combined with other techniques and theoretical modeling, PAC brings new insights on current cutting edge research on solid state physics: correlated electrons systems.
-The availability of different probes at Isolde allows tackling different situations: chemical compatibility and environments.