Effect of swift heavy ion irradiation in Fe/W multilayer structures

Sharmistha Bagchia, S. Potdara, F. Singhb, and N. P. Lallaa

a) UGC-DAE Consortiums for Scientific Research, Khandwa Road, Indore 452001. INDIAb) Inter University Accelerating Center (IUAC), Aruna Asaf Ali Marg, New Delhi 110067. INDIA

Abstract

The present study reports the effect of swift heavy ion irradiation on structural and magnetic properties of sputtered Fe/W multilayer structures (MLS) having bilayer compositions of [Fe(20Å)/W(10Å)]5BL and [Fe(20Å)/W(30Å)]5BL. These MLS were subjected to 120 MeV Au9+ ion irradiation up to fluence of 4×1013 ions/cm2. Pristine and irradiated MLS were subjected to structural and magnetic characterization employing wide-angle x-ray diffraction (WAXD), cross-sectional transmission electron microscopy (X-TEM) and magneto optical Kerr effect (MOKE).

Tailoring the properties of functional materials at atomic scale represents the ultimate goal in material science research. The most desirable approach is to artificially fabricate the structures with atomic precision, i.e. in layer-by-layer growth. For GMR application interface quality plays a decisive role in achieving the optimum performance. In order to optimize and understand these properties; structural studies regarding interface stability, against swift heavy ion-irradiation are done. To the best of our knowledge there is almost no reports of swift heavy ion irradiation study on immiscible systems like W/Fe [1, 2].

E-mail –bagchi.sharmistha@gmail.com

EXPERIMENTAL-DETAILES

W/Fe multilayer with composition [W(10,20,30)Å/Fe(20)Å]×5BL were deposited on Si-substrates by ion beam sputtering technique. The sample were irradiated by 120 MeV Au9+ ions at fluences between 5×1012 to 4×1013 ions/cm2. The irradiation was performed using the 15UD Pelletron accelerator at IUAC, New Delhi.The specimens were characterized before and after irradiation, using WAXD, XRR, X-TEM and MOKE.

E. Majkova, S. Luby, M. Jergel, A. Anopchenko, Y. Chushkin, G. Barucca, A. Cristoforo, P. Mengucci, E. D. Anna, A. Luches, M. Martino and H. Y. Lee Materials Science and Engineering C 19, (2002) 139. E. Majkova, S. Luby, M. Jergel, Y. Chushkin, E. D. Anna, A. Luches, M. Martino, P. Mengucci, G. Majni, Y. Kuwasawa and S. Okayasu Applied Surface Science 208, (2003) 394. S. Bagchi and N. P. Lalla, Thin Solid Films 515, (2007) 5227. S. Bagchi, S. Potdar, F. Singh and N. P. Lalla J. App. Phys. 102, (2007) 074310.S. Bagchi and N. P. Lalla. J. Phys.: Condens. Matter 20, (2008) 235202.

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IRRADIATION - STUDIES

The W-Fe system, with increasing bilayer thickness shows a weakly textured multilayer structure consisting of W layers oriented along [110] direction.

The SHI affects the inter-layer and intra-layer features in different ways. On irradiation the Fe-layers of the multilayer recrystallized of the individual layers into randomly oriented nano-crystals.

MOKE results show the change in coercivity and saturation value with irradiation dose, which is also consistence with the X-TEM data.

For direct observation and better understanding of the irradiation-induced microstructural changes, plane and cross-sectional TEM investigation on pristine as well as irradiated multilayer of W/Fe was carried out The observed alternate black and white layer-contrast is Z-contrast due to W and Fe layers [3, 4, 5].

INTRODUCTION OF SWIFT HEAVY ION IRRADIATION

REFERENCES

CONCLUSION

INTRODUCTION

This dominates at an energy of 1 keV

This dominates at an energy of 1 MeV or

more

Electronic Energy Loss (dE\dx)e

Nuclear Energy Loss (dE\dx)n

Thermal Spike Model

Energetic Ions

Coulomb Explosion

Magnetic Field (Oe)-1000 -500 0 500 1000

Pristine(a)

(c)

4x1013 ions/cm2

(b)

Ker

r int

ensi

ty (a

rb. u

nits

)

5x1012 ions/cm2

FeW10-5BL-Si FeW20-5BL-Si FeW30-5BL-Si

0.1 0.2 0.3 0.4 0.5

(a)

FeW10-5BL

4x1013 ions/cm2

5x1012 ions/cm2

pristine

Re

fle

ctivity

q(Å)-1

0.1 0.2 0.3 0.4

(b)

4x1013 ions/cm2

5x1012 ions/cm2

Pristine

FeW30-5BL

Ref

lect

ivity

q(Å)-1

Ref

lect

ivity

527101FeW30- 4×1013

35442FeW30- 5×1012

584132 FeW30- Pristine

59168FeW10- 4×1013

32959FeW10- 5×1012

46082 FeW10- Pristine

Saturation Field Value (Oe)

Coercivity Hc (Oe)

Multilayer Structure

FeW20-5BL

W(220)

W(110)/Fe(110)

W(200)W(211)/Fe(200)

W(321)W(400)

(b)(a)

1st

10nm

1st

(c) 10nm

W(220)W(211)

(d)

W(110)/Fe(110)W(200)

W(321)W(400)

W(110)/Fe(110)

W(200)W(211)

(f)

(a)

1st2nd

10nm

(d)

W(110)/Fe(110)

W(211)

W(110)/Fe(110)

Fe(200)

W(211)

(b)

W(110)/Fe(110)

W(200)

W(211)

(f)

(c)10nm

1st

2nd

(e)20nm

1st

(e)20nm

1st

2nd

Irradiated MLS

36 38 40 42 44 46

(a)

5x1012 ions/cm2

4x1013 ions/cm2

Pristine

Inte

nsi

ty (

arb

. u

nits

)

2 (Degree)

FeW10-5BL

38 40 42 44 46 48

Pristine

5x1012 ions/cm2

FeW30-5BL

4x1013 ions/cm2

Inte

nsi

ty (

arb

. u

nits

)

2 (Degree)

40 45

Inte

nsi

ty (

arb

. units

)FeW20-5BL

4x1013 ions/cm2

5x1012 ions/cm2

Pristine

2(degree)

FeW10

FeW10

Irradiated

FeW20 FeW20

Irradiated

FeW30

Irradiated

FeW30