Laboratory for Neutronen ScatteringETH Zurich & Paul Scherrer Institute

Jochen Stahn

Antiphase magnetic proximity effect

in perovskite

superconductor / ferromagnet multilayers

SFB 491 Seminar 23. 02. 2006Ruhr-Universitat Bochum

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 12π λ2δ(

z)·1

06z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

0

-1

-2

-3

0.01 0.02 0.03 0.04 0.05 0.06 0.07

qz/A−1

reflec

tivi

tylo

g[R

(qz)]

|+〉

|−〉

above TCurie

question: What is the magnetic induction

(profile) in HTSC /FM

multilayers?

method: polarised neutron reflectometry

allows for the determination of

ρ(z) and B‖(z)

answers: FM layers magnetised parallel

net magnetic moment in SC

at the interfaces, antiparallel

to FM magnetisation

SC creates and aligns domain

walls in FM

essence

1

1 LNS, ETHZ & PSI2 MPI-FKF, Stuttgart3 Universitat Fribourg

4 RUB / ILL5 FZ Julich

samples

G. Cristiani 2

HU. Habermeier 2

J. Hoppler 1

S. Pekarek 1

C. Niedermayer 1

E. Kenzinger 5

J. Chakhalian 2

analysis measurements

T. Gutberlet 1

U. Rucker 5

M. Wolff 4

interpretation

C. Bernhard 3

B. Keimer 2

cooperators:

2

general idea: the close contact of materials with different (alternative)

properties might lead to new phenomena

e.g. – interface of SrTiO3/LaTiO3 (insulators) is metallic

a multilayer reduces the dimension and forces the interaction

coupling phenomena might show up

e.g. – RKKY-interaction

– collosal magnetoresistance

– changed characteristic temperatures

present case: multilayers of a FM with a HTSC (both metals) seem to

show an metal/insulator transition in ellipsometry transition

for small periods — but stay superconducting / magnetic

so: what happens with the magnetisation and the

superconduction order parameter?

interfaces and layered systems “new physics” and “spintronics”?

3

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 12π λ2δ(

z)·1

06z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

0

-1

-2

-3

0.01 0.02 0.03 0.04 0.05 0.06 0.07

qz/A−1

reflec

tivi

tylo

g[R

(qz)]

|+〉

|−〉

above TCurie

question: What is the magnetic induction

(profile) in HTSC /FM

multilayers?

method: polarised neutron reflectometry

allows for the determination of

ρ(z) and B‖(z)

answers: FM layers magnetised parallel

net magnetic moment in SC

at the interfaces, antiparallel

to FM magnetisation

SC creates and aligns domain

walls in FM

overview

4

0 20 40 60 80 100 120 1400

10

20

30

40

100

150

200

Tc

Inte

rne

s M

ag

ne

tfeld

(G

)Temperatur (K)

Im Supraleiter Im Ferromagneten

Niederenergetische Myonen

0 50 100 150 2000.0

2.0x10-5

4.0x10-5

6.0x10-5

8.0x10-5

1.0x10-4

0.1 T 0.5 T 5 T

Mom

ent [

emu]

Temperature [K]

spring 2003:

C. Niedermayer presents nice µSR and

magnetisation measurements at PSI

enhanced magnetism below Tc

coexistence of FM and SC in RuSrCuGdO

→ competitive order parameters

artificial multilayers to investigate

– interaction of FM and SC at the interfaces and

– coupling through the layer

motivation / history:

5

0 20 40 60 80 100 120 1400

10

20

30

40

100

150

200

Tc

Inte

rne

s M

ag

ne

tfeld

(G

)Temperatur (K)

Im Supraleiter Im Ferromagneten

Niederenergetische Myonen

0 50 100 150 2000.0

2.0x10-5

4.0x10-5

6.0x10-5

8.0x10-5

1.0x10-4

0.1 T 0.5 T 5 T

Mom

ent [

emu]

Temperature [K]

spring 2003:

C. Niedermayer presents nice µSR and

magnetisation measurements at PSI

enhanced magnetism below Tc

method of choice

(for a neutron scatterer):

neutrons!

in particular polarised n-reflectometry

motivation / history:

6

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 12π λ2δ(

z)·1

06z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

0

-1

-2

-3

0.01 0.02 0.03 0.04 0.05 0.06 0.07

qz/A−1

reflec

tivi

tylo

g[R

(qz)]

|+〉

|−〉

above TCurie

question: What is the magnetic induction

(profile) in HTSC /FM

multilayers?

method: polarised neutron reflectometry

allows for the determination of

ρ(z) and B‖(z)

answers: FM layers magnetised parallel

net magnetic moment in SC

at the interfaces, antiparallel

to FM magnetisation

SC creates and aligns domain

walls in FM

overview

7

qz

q = kf − ki

ki kfz

V (z)

period

substrate

|+〉

|−〉

SCFM

ki kf

qzωω R

(ω)

layer thickness ratio 1:1⇒ extinction of evenBragg-peaks

interference of beams reflected from parallel interfaces

periodic structure ⇒ Bragg-condition for constructive interference

scattering potential:

V = Vnuc ± Vmag

= Vnuc + µB‖

reflectometry

8

YB

a 2Cu 3

O7

La 2

/3Ca 1

/3M

nO3

La

Ba

Y

Mn

Cu

O

materials: HTSC YBCO YBa2Cu3O7

FM LCMO La2/3Ca1/3MnO3

substr. STO SrTiO3

size: 10 × 10 mm2

(instead of 5 × 5 mm2)

produced: by Pulsed Laser Deposition

period: 200 A to 500 A

5 to 16 periods

ratios: 1 : 1 and 1 : 2

to cause extinction

non-rough interfaces

(otherwise used to tune Tc)

reflectometry tailored samples

9

sample holderwith absorber

closed cycle refrigerator8 K < T < 300 K

Helmholtz coilsH ≤ 1000 Oevol: 40 × 40 × 40 mm3

translation stages for alignment

ω-rotation stage

reflectometry sample environment (at SINQ):

10

detectordiaphragm

sample &environment

flipper & polariser

monochromator

ω2θ

qz

ω

R(ω

)

0

-1

-2

-3

0.01 0.02 0.03 0.04 0.05 0.06 0.07

qz/A−1

reflec

tivi

tylo

g[R

(qz)]

|+〉

|−〉

above TCurie

exam

ple

:

Mor

pheu

s@

SIN

Q

reflectometry

11

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 12π λ2δ(

z)·1

06z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

0

-1

-2

-3

0.01 0.02 0.03 0.04 0.05 0.06 0.07

qz/A−1

reflec

tivi

tylo

g[R

(qz)]

|+〉

|−〉

above TCurie

question: What is the magnetic induction

(profile) in HTSC /FM

multilayers?

method: polarised neutron reflectometry

allows for the determination of

ρ(z) and B‖(z)

answers: FM layers magnetised parallel

net magnetic moment in SC

at the interfaces, antiparallel

to FM magnetisation

SC creates and aligns domain

walls in FM

overview

12

0

-1

-2

-3

0.01 0.02 0.03 0.04 0.05 0.06 0.07

reflec

tivi

tylo

g[R

(qz)]

1st

2nd

3rd

above TCurie

|+〉 , 10 K

|−〉 , 10 K

��

��

��

��

��

���

��

��

��

��

��

��

��

���7

�����������������������

6

splitting of the edge of total reflection⇒ changed potential of the surface

no half-order Bragg-peak⇒ parallel alignment of B in the FM layers

intensity variation of the 1st Bragg-peak⇒ changed potential in the FM layersB‖ can be determined

appearance of a 2nd order Bragg-peak⇒ B‖(z) and Vnuc(z) have different symmetry

H = 100 Oe

field cooled

T = 10, 300 K

reflectometry direct interpretation

13

LCMOYBCO

(z)B

cosh-functions

off-sets with

constant B

simulations performed with EDXR by Petr Mikulık (no fitting)

bilayer structure has been broken down to

some 100 sublayers to pay respect to B(z).

analytic expressions for B(z):

decrease of layer thickness towards the borders taken into account

reflectometry simulations

14

zδ

δ(z)

zδ

δ(z)

|−〉 |+〉

LCMO

YBCO

STO

0

-1

-2

-3

reflec

tivi

tylo

g[R

(qz)]

1st

2nd

3rd|+〉

|−〉

above TCurie

cal c

ul a

t ed

-4

-3

-2

-1

0

0.01 0.02 0.03 0.04 0.05 0.06 0.07

qz/A−1

reflec

tivi

tylo

g[R

(qz)]

|+〉

|−〉

above TCurie

sample:

[YBCO(150 A)/LCMO(140 A)]5

reflectometry simulation specular, polarised

15

zδ

δ(z)

zδ

δ(z)

|−〉 |+〉

LCMO

YBCO

STO

0

-1

-2

-3

reflec

tivi

tylo

g[R

(qz)]

1st

2nd

3rd|+〉

|−〉

above TCurie

cal c

ul a

t ed

-4

-3

-2

-1

0

0.01 0.02 0.03 0.04 0.05 0.06 0.07

qz/A−1

reflec

tivi

tylo

g[R

(qz)]

|+〉

|−〉

above TCurie

too

si m

pl e

!

δmag(z) 6= δnuc(z) ×

0 for YBCO

const for LCMO

sample:

[YBCO(150 A)/LCMO(140 A)]5

reflectometry specular, polarised

16

0

-1

-2

-3

reflec

tivi

tylo

g[R

(qz)]

1st

2nd

3rd|+〉

|−〉

above TCurie

cal c

ul a

t ed

-4

-3

-2

-1

0

0.01 0.02 0.03 0.04 0.05 0.06 0.07

reflec

tivi

tylo

g[R

(qz)]

qz/A−1

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1

2π λ2δ(

z)·1

06

z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

sharp contrast at the interface

exponential decay into YBCO

AFM exponential decay into YBCO

penetration into YBCO

magnetically dead layer in LCMO

modelling magnetic profile at the interfaces

17

0

-1

-2

-3

reflec

tivi

tylo

g[R

(qz)]

1st

2nd

3rd|+〉

|−〉

above TCurie

cal c

ul a

t ed

-4

-3

-2

-1

0

0.01 0.02 0.03 0.04 0.05 0.06 0.07

reflec

tivi

tylo

g[R

(qz)]

qz/A−1

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1

2π λ2δ(

z)·1

06

z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

sharp contrast at the interface

exponential decay into YBCO

AFM exponential decay into YBCO

penetration into YBCO

magnetically dead layer in LCMO

modelling magnetic profile at the interfaces

18

0

-1

-2

-3

reflec

tivi

tylo

g[R

(qz)]

1st

2nd

3rd|+〉

|−〉

above TCurie

cal c

ul a

t ed

-4

-3

-2

-1

0

0.01 0.02 0.03 0.04 0.05 0.06 0.07

reflec

tivi

tylo

g[R

(qz)]

qz/A−1

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1

2π λ2δ(

z)·1

06

z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

sharp contrast at the interface

exponential decay into YBCO

AFM exponential decay into YBCO

penetration into YBCO

magnetically dead layer in LCMO

modelling magnetic profile at the interfaces

19

0

-1

-2

-3

reflec

tivi

tylo

g[R

(qz)]

1st

2nd

3rd|+〉

|−〉

above TCurie

cal c

ul a

t ed

-4

-3

-2

-1

0

0.01 0.02 0.03 0.04 0.05 0.06 0.07

reflec

tivi

tylo

g[R

(qz)]

qz/A−1

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1

2π λ2δ(

z)·1

06

z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

sharp contrast at the interface

exponential decay into YBCO

AFM exponential decay into YBCO

penetration into YBCO

magnetically dead layer in LCMO

modelling magnetic profile at the interfaces

20

0

-1

-2

-3

reflec

tivi

tylo

g[R

(qz)]

1st

2nd

3rd|+〉

|−〉

above TCurie

cal c

ul a

t ed

-4

-3

-2

-1

0

0.01 0.02 0.03 0.04 0.05 0.06 0.07

reflec

tivi

tylo

g[R

(qz)]

qz/A−1

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1

2π λ2δ(

z)·1

06

z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

sharp contrast at the interface

exponential decay into YBCO

AFM exponential decay into YBCO

penetration into YBCO

magnetically dead layer in LCMO

modelling magnetic profile at the interfaces

21

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1

2π λ2δ(

z)·1

06

z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1

2π λ2δ(

z)·1

06

z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

PNR at RT and below TCurie and Tc

exclude all models besides

AFM-region within LCMO

charge-injection from YBCO leads to

a doping of LCMO and thus to an

AFM ground state

antiphase magnetic proximity

effect

AF coupling of Mn and Cu moments

through oxygen

or

Cooper pairs penetrate into LCMO

and are polarised

⇒ antiparallel magnetisation in YBCO

resume

22

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1

2π λ2δ(

z)·1

06

z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1

2π λ2δ(

z)·1

06

z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

PRB 69, 174504 (2004):

PNR at RT and below TCurie and Tc

exclude all models besides

AFM-region within LCMO

charge-injection from YBCO leads to

a doping of LCMO and thus to an

AFM ground state

resume

23

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

-1 -0.5 0 0.5 1

mag

net

isat

ion

10−

7A

m2

H/103 Oe

SQUID measurements by F. Treubel, Konstanz

T = 5 K

cooled in H = 100 Oe

coercitive field Hco ≈ ±400 Oe

exchange bias Heb ≈ −60 Oe

⇓

presence of an AFM coupling

at the FM-interface

but:

– magnetically dead layer might be an AFM

– B in YBCO might be an AFM with net magnetic moment

magnetometry

24

-4

-3

-2

-1

0

0.02 0.04 0.06 0.08 0.1

qz/A−1

log[

R(q

z)]

1st Bragg peak

2nd Bragg peak

200K

15K

0.5

1

1.5

2

2.5

3

0 50 100 150 200 250 300

T / K

R(T

)/R

(RT

)

1st Bragg peak

|+〉

|−〉2nd Bragg peak

|+〉

|−〉

Tc

T ′ TCurie

[YB

CO

(100

A)/

LCM

O(1

00A

)]7

[YB

CO

(200

A)/

LCM

O(2

00A

)]8

TCurie (160 → 270 K)

onset of FM: changed contrast

T ′ (≈ 140 K)

formation of 2nd peaks

B(z) and Vnuc(z) differ

Tc (60 → 90 K)

onset of SC

T dependence of R(qz)

25

-4

-3

-2

-1

0

0.02 0.04 0.06 0.08 0.1

qz/A−1

log[

R(q

z)]

1st Bragg peak

2nd Bragg peak

200K

15K

0.5

1

1.5

2

2.5

3

0 50 100 150 200 250 300

T / K

R(T

)/R

(RT

)

1st Bragg peak

|+〉

|−〉2nd Bragg peak

|+〉

|−〉

Tc

T ′ TCurie

[YB

CO

(100

A)/

LCM

O(1

00A

)]7

[YB

CO

(200

A)/

LCM

O(2

00A

)]8

Te

mp

era

ture

An

tife

rro

ma

gn

etic Pseudogap

Fermi liquid

Non Fermi liquid

Doping level (holes per CuO )2

Underdoped Optimally doped Overdoped

Superconducting

?

�

T ∗

T ′TCurie

TCurie (160 → 270 K)

onset of FM: changed contrast

T ′ ≈ T ∗ (≈ 140 K)

formation of 2nd peaks

B(z) and Vnuc(z) differ

Tc (60 → 90 K)

onset of SC

T dependence of R(qz)

26

0

0.5

1

1.5

2

2.5

3

3.5

4

120 140 160 180 200

T/K

R(T

)/R

(RT

)

1st Bragg peak

|+〉

|−〉2nd Bragg peak

|+〉 + |−〉T ′

TCurie

0.5

1

1.5

2

2.5

3

0 50 100 150 200 250 300

T / K

R(T

)/R

(RT

)

1st Bragg peak

|+〉

|−〉2nd Bragg peak

|+〉

|−〉

Tc

T ′ TCurie

[YPB

CO

(200

A)/

LCM

O(2

00A

)]8

Y0.6Pr 0

.4B

a 2Cu 3

O7

[YB

CO

(200

A)/

LCM

O(2

00A

)]8

Te

mp

era

ture

An

tife

rro

ma

gn

etic Pseudogap

Fermi liquid

Non Fermi liquid

Doping level (holes per CuO )2

Underdoped Optimally doped Overdoped

Superconducting

?

����

T ′

T ∗

T ′TCurie

T ′ ≈ T ∗ varies with doping!

T dependence of R(qz)

27

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 12π λ2δ(

z)·1

06z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

0

-1

-2

-3

0.01 0.02 0.03 0.04 0.05 0.06 0.07

qz/A−1

reflec

tivi

tylo

g[R

(qz)]

|+〉

|−〉

above TCurie

question: What is the magnetic induction

(profile) in HTSC /FM

multilayers?

method: polarised neutron reflectometry

allows for the determination of

ρ(z) and B‖(z)

answers: FM layers magnetised parallel

net magnetic moment in SC

at the interfaces, antiparallel

to FM magnetisation

SC creates and aligns domain

walls in FM

overview

28

k0

kR,in−plane off−specular

kR,specular

kR,out−of−plane off−specular

qxz

qzqxyz

in our cases:resolution in x : ≈ 0.01◦

resolution in y : > 1◦

⇒ integrated over y

inclined surface facetts ⇒ ∆ω

height-variation ⇒ phase-shifts in kR

⇒ damping of R(qz > qc)

neutron scattering probes

a potential parallel to q

if q 6= q(z) also lateral

structure is accessible

here:

lateral and vertical

correlation length of

(magnetic) inhomogeneities

off-specular scattering principle

29

|+〉 , |+〉 |−〉 , |−〉 |+〉 , |−〉

10

0

10

20

0 10 2010

0

10

20

0 10 2010

0

10

20

0 10 20

10

0

10

20

0 10 2010

0

10

20

0 10 2010

0

10

20

0 10 20

10

0

10

20

0 10 2010

0

10

20

0 10 2010

0

10

20

0 10 20

exit

angl

eα

f/

mra

d

20

10

0

-10

20

10

0

-10

20

10

0

-10

angle of incidence αi / mrad0 10 20 0 10 20 0 10 20

ab

c

d

eXXXXXX

T=

200

KT

=16

0K

T=

130

K

No off-specular sheets at RT or 200 K⇒ no structural roughness detectable

Increase of the Bragg sheet at 1st

Bragg peak (d) below 160 K⇒ magnetic roughness, correlatedvertically

Appearance of sheets in the spin-flipchannel (e)⇒ magnetic moments not parallel tothe neutron spins

Interpretation (of all measurements):Magnetic domains of similar size (≈ 5to 10µm) are formed in the LCMOlayers. These are correlated throughYBCO over the whole stack.

off-specular scattering measured on HADAS@Julich

30

50100150200250

-1 -0.5 0 0.5 1

T/

K

qx / 10−4A−1

1

2

3

4

0 50 100 150 200 250

T / K

log[

R(q

z)]

integratd over qx

at peak positions

Tc

TCurie -4

-3

-2

-1

0

0.02 0.04 0.06 0.08 0.1

qz/A−1

reflec

tivi

tylo

g[R

(qz)]

1st Bragg peak

200 K

15 K

non-polarised, various T

sample: [YBCO(100 A)/LCMO(100 A)]7

magnetic domains shrink below Tc

from 10 µm to 5 µm when cooling

off-specular scattering ω-scans

31

TCurie

T ′

Tc

B‖

• all LCMO layers are magnetised parallel

• interface effect of B(z) of the order of10 A is measuredat Tc < T ′ ≈ 140 K < TCurie

– magnetic dead layer or antiphase

proximity effect

• simultaneous appearance of Bragg-sheets

– vertical correlation of magnetic domains

• increase of off-specular scattering belowTc

– shrinking of magnetic domains/ characteristic lengthscale

• correlation of domain size with T < Tc

and XMCD measurements support theantiphase proximity effect

conclusion:

32

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 12π λ2δ(

z)·1

06z/d in one period

YBCO LCMO

|+〉

nuc

|−〉

mag

LCMO

0

-1

-2

-3

0.01 0.02 0.03 0.04 0.05 0.06 0.07

qz/A−1

reflec

tivi

tylo

g[R

(qz)]

|+〉

|−〉

above TCurie

question: What is the magnetic induction

(profile) in HTSC /FM

multilayers?

method: polarised neutron reflectometry

allows for the determination of

ρ(z) and B‖(z)

answers: FM layers magnetised parallel

net magnetic moment in SC

at the interfaces, antiparallel

to FM magnetisation

SC creates and aligns domain

walls in FM

essence

33

THE END