1

Structure-related changes in magnetoresistance of Co90Fe10/Cu and Co90Fe10/Cu85Ag10Au5 multilayers

D. RafajaInst. of Physical Metallurgy, TU Bergakademie

FreibergJ. Ebert, G. Miehe, N. Martz, M. Knapp, B. Stahl, M. Ghafari, H. Hahn and H. Fuess

Inst. of Materials Science, TU DarmstadtP. Schmollengruber, P. Farber and H.Siegle

Robert Bosch GmbH, Stuttgart

2

GMR multilayers Co90Fe10/(Cu,Ag,Au)

Si (111)

SiO2 (750 m)

Fe (4.4 nm)

Co90Fe10 (1.1 nm)

Cu (2.2 nm)20x

Si (111)

SiO2 (750 m)

Fe (4.4 nm)

Co90Fe10 (1.1 nm)

Cu85Ag10Au5 (2.2 nm)

Co90Fe10/Cu Co90Fe10/Cu85Ag10Au5

Soft annealing: 1 hour at 220-360°C

substrate

buffer

3

Magnetoresistance

-100 -50 0 50 100

0

5

10

15

20

25

B (mT)

-100 -50 0 50 1000

5

10

15

20

25

GM

R (

%)

B (mT)

Co90Fe10/Cu Co90Fe10/Cu85Ag10Au5

200 250 300 3505

10

15

20

25

GM

R (

%)

T (°C)

Co90Fe10/Cu

Co90Fe10/ Cu85Ag10Au5

4

Anomalous X-ray scattering

iii

iii

e

fcffcf

fffr

n

;

21 0

2

T.Bigault, F.Bocquet, S.Labat, O.Thomas and H.Renevier, Phys.Rev.B 64 (2001) 125414.

26Fe 27Co 28Ni 29Cu

47Ag

79Au

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

1.0

1.5

2.0

2.5

3.0

Cu

Co 90Fe 10

Cu

Cu 85Ag10Au5

Re

al(

1-n

)*1

05

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Co 90Fe 10

Cu 85Ag10Au5

Ima

g(n

)*1

06

Wavelength (Å)

5

Experimental set-up (conventional)

X-ray tubeCuK

Göbel mirror

Sample

Secondary graphite monochromator

Detector

Slit 0.1mm

Slit 0.05 mm

= 1.5418 Å

Seifert – PTS

6

Experimental set-up (HASYLAB)

Mirror

Sample

Secondary graphite monochromator

Detector

Slit 0.1mm

Slit 0.05 mmBeamline B2

2xGe(111)

PETRA

= 1.13 Å = 1.37 Å = 1.39 Å

Huber – Eulerian cradle

7

Virgin multilayer (Co90Fe10/Cu)20

0.0 0.1 0.2 0.3 0.4 0.5100

101

102

103

104

105

106

107

108

109

1010

-4 -2 0 2 410

1

102

103

104

Inte

nsi

ty (

a.u

.)

qx (10

-3Å

-1)

Inte

nsi

ty (

a.u

.)

qz = 4 sin (1 /Å)

0 10 20 30 40

0.2

0.4

0.6

0.8

1.0

1.2

Ele

ctro

n d

en

sity

Number of layer (from top)

0 10 20 30 40

5

10

15

20

25

Th

ickn

ess

(Å

)

0 10 20 30 40

0

5

10

15

20

25

30

35 J415, 1 .37Å

J415, 1 .39Å

J415, 1 .54Å

Ro

ug

hn

ess

(Å

)

-4 -2 0 2 410

1

102

103

104

Inte

nsi

ty (

a.u

.)

qx (10-3Å-1)

[Å]

1.5418

1.39

1.37

1.13

8

TEM and SAED

TEM at a strong overfocus

SAED(diameter 250 nm)

9

Annealed multilayer (Co90Fe10/Cu)20

t (CoFe) [nm] t (Cu) [nm]

20°C (1.16±0.12) (2.06±0.11)235°C (1.16±0.12) (2.04±0.15)340°C (1.19±0.13) (2.02±0.20)

(CoFe) [nm] (Cu) [nm]

20°C (0.73±0.21) (0.88±0.20)235°C (0.83±0.27) (1.03±0.20)340°C (0.87±0.30) (1.15±0.30)

Refined parameters

0 1 2 3 4 510

0

101

102

103

104

105

106

107

108

109

1010

-4 -2 0 2 4

101

102

103

104

Inte

nsi

ty (

a.u

.)

qx (10

-3Å

-1)

Inte

nsi

ty (

a.u

.)

qz = 4 sin (1 /nm)

-4 -2 0 2 4

101

102

103

104

Inte

nsity

(a

.u.)

qx (10-3Å

-1)

XRR: = 1.37Å ; : = 1.39 Å

Interface discontinuity at 340°C

10

Annealed multilayer (Co90Fe10/Cu)20

35 40 45 50

50

100

150

200

250

300

Inte

ns

ity (

arb

.un

its)

Diffraction angle (o2)

As prepared

235°C

340°C

111 Cu

1 hour

= 1.5418Å

11

Virgin multilayer (Co90Fe10/Cu85Ag10Au5)20

0.0 0.1 0.2 0.3 0.4 0.510

0

101

102

103

104

105

106

107

108

109

Inte

nsi

ty (

a.u

.)

q = 4 sin (1/Å)

0.0 0.1 0.2 0.3 0.4 0.5100

101

102

103

104

105

106

107

108

109

1010

-4 -2 0 2 410

1

102

103

104

Inte

nsi

ty (

a.u

.)

qx (10

-3Å

-1)

Inte

nsi

ty (

a.u

.)

qz = 4 sin (1 /Å)

[Å]

1.5418

1.39

1.37

Co90Fe10/Cu

12

Virgin multilayer (Co90Fe10/Cu85Ag10Au5)20

0 10 20 30 40

0.2

0.4

0.6

0.8

1.0

1.2

Ele

ctro

n d

en

sity

Layer number (from top)

0 10 20 30 40

0

5

10

15

20

25

30

35

Th

ickn

es

s (Å

)

0 10 20 30 40

0

5

10

15

20

25

30

J327 , 1.37Å

J327 , 1.39Å

J327 , 1.54Å

Ro

ug

hn

es

s (Å

)

0 10 20 30 40

0.2

0.4

0.6

0.8

1.0

1.2

Ele

ctro

n d

en

sity

Number of layer (from top)

0 10 20 30 40

5

10

15

20

25

Th

ickn

ess

(Å

)

0 10 20 30 40

0

5

10

15

20

25

30

35 J415, 1 .37Å

J415, 1 .39Å

J415, 1 .54Å

Ro

ug

hn

ess

(Å

)

Co90Fe10/CuCo90Fe10/Cu85Ag10Au5

13

Annealed multilayer (Co90Fe10/Cu85Ag10Au5)20

Refined parameters

0 1 2 3 4 510

0

101

102

103

104

105

106

107

108

109

1010

-4 -2 0 2 410

0

101

102

103

104

105

Inte

ns

ity

(a.u

.)

qx (10

-3Å

-1)

Inte

nsi

ty (

a.u

.)

qz = 4 sin (1 /nm)

t (CoFe) [nm] t (CuAgAu) [nm] 20°C (1.14±0.13) (2.09±0.11)235°C (1.13±0.12) (2.08±0.12)340°C (1.09±0.14) (2.11±0.14)

(CoFe) [nm] (CuAgAu) [nm] 20°C (0.75±0.28) (0.89±0.20)235°C (0.75±0.30) (0.93±0.25)340°C (0.83±0.34) (1.07±0.23)

-4 -2 0 2 410

0

101

102

103

104

105

Inte

nsi

ty (

a.u

.)

qx (10

-3Å

-1)

No interface discontinuity at 340°C

14

Annealed multilayer (Co90Fe10/Cu85Ag10Au5)20

35 40 45 50

50

100

150

200

250

300

Inte

nsi

ty (

arb

.un

its)

Diffraction angle (o2)

As prepared

235°C

340°C

111 Cu

1 hour

15

Structure model for Co90Fe10/Cu

Cu

CoFe

Cu

CoFe

annealing

Cu

CoFe

Cu

Increase of interface roughness. Onset of interface discontinuity.

16

Structure model for Co90Fe10/Cu85Ag10Au5

Cu(Au)

CoFe

annealing

Cu

Ag Ag

Increase of interface roughness. Separation of gold and silver.

Au

17

Conclusions

Annealing at 235°C initiated out-diffusion of Co and Cu and an increase of the interface roughness in both systems still, the GMG effect was improved

Annealing at higher temperatures led to degradation of the multilayer structure and to the decrease of GMR:– Co90Fe10/Cu – discontinuity of interfaces

– Co90Fe10/Cu85Ag10Au5 – precipitation of Ag and Au at the surface (Ag) and within the layers (Au)