local probe studies in manganites and complex oxides

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







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







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.







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


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


TCO

CO region, Vzz vs Temperature

T*


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*


Sharp increase of Vzz @ T< TCO

Dropping @ T*

EFG and magnetic susceptibility


From NMR and PAC studies in Ferroelectrics

el20

zz βTχαPVVsZZ

Susceptibility Increase

LocalSpontaneous Polarization

TC

EFG sensitive to atomic vibrations and critical fluctuations


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


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







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?







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







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.

local probe studies in manganites and complex oxides

Documents

electric fields

charge ordering

perturbed angular correlations

manganites charge

magnetic field

polaron dynamics

pr1xcaxmno3 new paradigm

ordered wayphase separation