dynamic phase separation in manganites

35
Dynamic Phase Separation in Manganites Luis Ghivelder IF/UFRJ – Rio de Janeiro Francisco Parisi CNEA – Buenos Aires

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Dynamic Phase Separation in Manganites. Luis Ghivelder IF/UFRJ – Rio de Janeiro Francisco Parisi CNEA – Buenos Aires. Where was this research carried out ?. Low Temperatures Laboratory, Physics Institute Federal University of Rio de Janeiro. Extraction Magnetometer - 9 T PPMS. - PowerPoint PPT Presentation

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Page 1: Dynamic Phase Separation in Manganites

Dynamic Phase Separation in Manganites

Luis GhivelderIF/UFRJ – Rio de Janeiro

Francisco ParisiCNEA – Buenos Aires

Page 2: Dynamic Phase Separation in Manganites

Where was this research carried out ?

Low Temperatures Laboratory, Physics InstituteFederal University of Rio de Janeiro

Page 3: Dynamic Phase Separation in Manganites

Extraction Magnetometer - 9 TPPMS

VSM – 14 T SQUID - 6 T Cryogenics

Page 4: Dynamic Phase Separation in Manganites

Why are manganites so interesting ?

Colossal Magnetoresistanc

e

CMR

Started with

Page 5: Dynamic Phase Separation in Manganites

1114 citations !

Page 6: Dynamic Phase Separation in Manganites

FM

CO

AF CAF

FI

CO

CAF

Ca x

Tem

pera

ture

(K

)

x = 1/8

3/84/8

5/8

7/8

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

Phase Diagram of La1-xCaxMnO3

Complexity in Manganites:

Page 7: Dynamic Phase Separation in Manganites

Main ingredient for understanding the Manganites

Ferromagnetic metallic

t2g

eg

Mn4+Mn3+

Antiferromagnetic Charge ordered

insulating

competition between

and

Micrometer or Nanometer scale

Phase Separation (PS)

Page 8: Dynamic Phase Separation in Manganites

Qualitative (naïve) picture

AFM-COinsulating

FMmetallic

H = 0H

CMRPhase

Separation

Page 9: Dynamic Phase Separation in Manganites

La5/8-xPrxCa3/8MnO3

Prototype compound for studying Phase Separation in manganites

0 50 100 150 200 250 300

0.1

1

TN

(AFM)

TCO

(CO)

TC

(FM)

x = 0.6Pr rich

x = 0.1La rich

H = 1 T

M

(B

/ Mn)

T(K)

0 50 100 150 200 250 300

0.1

1

FCW

FCC PhaseSeparation

0.6

x = 0.4

x = 0.3

x = 0.1

H = 1 T

M

(B

/ M

n)

T(K)

Page 10: Dynamic Phase Separation in Manganites

x = 0.4 La0.225Pr0.40Ca0.375MnO3

0 50 100 150 200 250 300

0.1

1 FCW

FCC

H = 1 T

M(

B /

Mn

)

T(K)PM

COAFM-CO

FM

FCC curve mostly FM at low temperatures

0 50 100 150 200 250 300

0.1

1

ZFC

FCW

FCC

H = 1 T

M(

B /

Mn

)

T(K)

ZFC curve metastable frozen state at low temperatures

Magnetic Glass

TCO

TN

TCTB

TC

Blocking temperature

Page 11: Dynamic Phase Separation in Manganites

Correlation between magnetic and transport properties

0 50 100 150

100

101

102

103

104

0.0

0.4

0.8

1.2

(.

cm)

T (K)

H = 1 T

ZFC FCC FCW

M ( B

/Mn)

0 50 100 150

100

101

102

103

104

0.0

0.4

0.8

1.2

(.

cm)

T (K)

H = 1 T

virgin magnetization

ZFC FCC FCW

M ( B

/Mn)

Page 12: Dynamic Phase Separation in Manganites

Dynamics of the phase separated

state

Relaxation measurements

0 50 100 150 200 2500.0

0.3

0.6

0.9

M

( B

/ M

n)

H = 1 T, FCC

T (K)

0 50 100 150 200 2500.0

0.3

0.6

0.9

M

( B

/ M

n)

H = 1 T, FCC

T (K)

0 50 100 150 200 2500.0

0.3

0.6

0.92 hours

M

( B

/ M

n)

H = 1 T, FCC

T (K)

Page 13: Dynamic Phase Separation in Manganites

Thermal cycling

0 20 40 60 800.0

0.3

0.6

0.9

H = 1 T, ZFC

M ( B

/Mn)

T (K)

0 20 40 60 800.0

0.3

0.6

0.9

H = 1 T, ZFC

M ( B

/Mn)

T (K)

0 20 40 60 800.0

0.3

0.6

0.9

H = 1 T, ZFC

M ( B

/Mn)

T (K)

0 20 40 60 800.0

0.3

0.6

0.9

H = 1 T, ZFC

M ( B

/Mn)

T (K)

0 20 40 60 800.0

0.3

0.6

0.9

H = 1 T, ZFC

M ( B

/Mn)

T (K)

Page 14: Dynamic Phase Separation in Manganites

ZFC Relaxation

0 2000 4000 6000 8000

1.0

1.2

1.4

1.6

1.8

10 K

M/M

(0)

t (sec)

0 20 40 60 80 1000.0

0.3

0.6

0.9

1.2

ZFC, H = 1 T

M(

B)

T (K)0 20 40 60 80 100

0.0

0.3

0.6

0.9

1.2

ZFC, H = 1 T

M(

B)

T (K)0 20 40 60 80 100

0.0

0.3

0.6

0.9

1.2

ZFC, H = 1 T

M(

B)

T (K)

20 K

50 K

0 20 40 60 80 1000.0

0.3

0.6

0.9

1.2

ZFC, H = 1 T

M(

B)

T (K)0 20 40 60 80 100

0.0

0.3

0.6

0.9

1.2

ZFC, H = 1 T

M(

B)

T (K)

80 K

Magnetic Viscosity S(T)

)()1/ln()(),( 00 TMttTStTM

Page 15: Dynamic Phase Separation in Manganites

Phenomenological model

Hierarchical dynamic evolution

most probable event happens before the lesser probable

one

Collective behavior evolution is described in terms of a single variable

Time evolution through a hierarchy of energy barriers, which separates the

coexisting phases

Page 16: Dynamic Phase Separation in Manganites

Conventional activated dynamic functional with state-dependent energy

barriers.

T

HxU

eq

eq evxx

xx

dtdx ),(

0||

)(

)(Tx Normalized FM fraction

Proportional to the

Magnetization

EquilibriumFM fraction

Arrhenius-like activation

Diverging energy barriers

||

)(),(

xx

HUHxU

eq ),( HTxeq

Page 17: Dynamic Phase Separation in Manganites

dtevtxdttx T

THxU

][)()(),,(

0

)(Txeq Linear from 0)80( Kxeq 1)20( Kxequnti

l

Numerical simulation

Solid line: numerical simulation

Page 18: Dynamic Phase Separation in Manganites

Melting of the AFM-CO state

Metamagnetictransition

Alignment of the small FM fraction

Homogeneous and

irreversible FM state

Page 19: Dynamic Phase Separation in Manganites
Page 20: Dynamic Phase Separation in Manganites

See talk by De Lozzane tomorrow

Page 21: Dynamic Phase Separation in Manganites

Abrupt field-induced transition at low temperaturesAvalanche, Jumps,

Steps

At very low temperatures

T = 2.5 K

Ultrasharp metamagnetic

transition

Page 22: Dynamic Phase Separation in Manganites

Temperature variation of the magnetization jumps

Page 23: Dynamic Phase Separation in Manganites

Magnetization jumps Relaxation

enlarged view

H = 23.6 kOe

H = 23.8 kOe

H = 24.0 kOe

H = 23.6 kOe

Page 24: Dynamic Phase Separation in Manganites

Spontaneous metamagnetic transition

H = 23.6 kOe

Page 25: Dynamic Phase Separation in Manganites

Open Questions

What causes these magnetization jumps ?

Why it only happens at very low temperatures ?

Martensitic scenario vs.

Thermodynamical effect

Page 26: Dynamic Phase Separation in Manganites

Magnetocaloric effectHuge sample temperature rise at the magnetization

jump

heat generated when the non-FM fraction of the material is converted to the FM phase

k

0 20 40 60 80 1000.0

0.3

0.6

0.9

1.2

ZFC, H = 1 T

M(

B)

T (K)

Page 27: Dynamic Phase Separation in Manganites

La5/8-xNdxCa3/8MnO3 , x = 0.5

0 20 40 60 80

0

2

4

T = 2.5 K

M ( B

/Mn)

H (kOe)

0

3

6

9

12

15

18

21

Tsa

mpl

e (K

)

T = 2.5 K

0 20 40 60 80

0

2

4

M ( B

/Mn)

H (kOe)

T = 6 K

6.0

6.5

7.0

7.5

8.0

Tsa

mpl

e (K

)

Nd based manganite

Page 28: Dynamic Phase Separation in Manganites

Microscopic mechanisms promote locally a FM volume increase, which yield a local

temperature rise, and trigger the avalanche process.

Our model

The entity which is propagated is heat, not magnetic domain walls, so the roles of grain boundaries or strains

which exist between the coexisting phases are less relevant

PS and frozen metastable states are essential ingredients for the magnetization jumps

Page 29: Dynamic Phase Separation in Manganites

Constructing a ZFC phase diagram

M vs. T

M vs. H

Page 30: Dynamic Phase Separation in Manganites

H-T phase diagram

FMhomogeneous

AFM-COPS

dynamic

PS

frozen

Page 31: Dynamic Phase Separation in Manganites

x = 0.3 La0.325Pr0.30Ca0.375MnO3

data by M. Quintero

A different compound, with PS at intermediate temperatures

Page 32: Dynamic Phase Separation in Manganites

Magnetic field tuned

equilibrium FM fraction

Page 33: Dynamic Phase Separation in Manganites

Summary

Quenched disorder leads to the formation of inhomogeneous metastable states

ZFC process in phase separated manganites:

Dynamic nature of the phase separated state:

Equilibrium ground state is not reached in laboratory time

Large relaxation effects are observed in a certain temperature window

Page 34: Dynamic Phase Separation in Manganites

References of our work

Page 35: Dynamic Phase Separation in Manganites