Scaling in the Roughness of Transition Metal Multilayers

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Scaling in the Roughness of Transition Metal
Multilayers

• Amir S. H. Rozatian
• In collaboration with
• A. T. G. Pym, T. P. A. Hase,
• B. K. Tanner, C. H. Marrows,
• S. Brown, L. Bouchenoire

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Acknowledgments

• Durham University, UK X-ray and Magnetism Group
• Leeds University, UK Prof. B J Hickey and his
  group
• Isfahan University, IRAN Department of Physics
• SRS, Station 2.3, Daresbury, UK
• ESRF, XMaS Beamline (BM 28), Grenoble, France
• Organizers of the 3rd SESAME Users Meeting

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Aims

• To study the in-plane and out-of-plane
  correlation lengths and scaling behaviour of the
  conformal interface roughness of sputtered Co/Pd
  and Co/Ru multilayers.

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Outline of Talk

• 1_ Introduction
• 2_ Theoretical Models KPZ and TAB models
• 3_ GISAXS and MAR CCD techniques
• 4_ Results
• 5_ Conclusions
• 6_ Future Work

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Introduction
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Evolution of the Interface Morphology

• The evolution of the interface morphology during
  the growth of thin films and multilayers has a
  major impact on the overall magnetic and
  transport properties. In particular, the
  mechanism of roughness propagation from the
  substrate to the surface has been the focus of a
  number of experimental and theoretical studies.

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Roughness Profile
Zero roughness
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Theoretical Models
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TAB Model

• Huygens Principle
• Columnar Structure
• Longer spatial
• wavelengths
• propagate more easily

Tang C, et al, Phys. Rev. Lett. 64 (1990) 772
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Parameters of a surface
?3
?1
?2
y1
y2
x2
x1
For a self-similar surface
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KPZ model

• The variation of the local height of the surface
  H(x,t)
• Interfacial tension
• Tends to smooth the interface, for

M. Kardar, G. Parisi, and Y. C. Zhang, Phys. Rev.
Lett., 56 (9), 889-892 (1986).
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KPZ model
Partially correlated system
Uncorrelated system
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KPZ model
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Magneto-Optical Disc (MOD)

• Writing The disc is heated locally by a pulse
  of a diode laser beam which is focused to a spot
  of about 1 ?m. The magnetization is reversed only
  in the area of the heated spot by applying a
  small field, which is smaller than the coercive
  field of the MO layer at room temperature but
  larger than the coercive field in the heated
  area.
• Reading The same laser reads back the written
  bits making use of the polar MOKE.

1 MOD? 500 DVD
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Experimental Techniques (determining roughness)
SR or Lab?
Do we have to take all samples to a 3rd
generation SR?
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X-ray Data Collection
Intensity
? ? h
Scattering vector
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GIXR and GIXS data and Simulations for Co/Pt
Multilayers (using BEDE software)
Fulthorpe et al, J. Phys. C., 11(43), (1999)
p8477 Rozatian et al, J. Mag. Magn. Mater. Vol.
256 (1-3), (2003) p365
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MAR CCD detector
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Comparison of CCD to conventional detector
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Results
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Co/Pd system(GIXR and GIXS results)
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Co/Pd multilayers(Relation between the
out-of-plane correlation length and N)

• High frequency components of roughness do not
  propagate well through Co/Pd layers.
• Low frequency components of the conformal
  roughness propagate well with a much longer out
  of plane correlation length.

The out-of plane correlation length of the
conformal roughness in Co-Pd multilayers,
submitted to Physica B.
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Co/Pd multilayers(Relation between the in-plane
correlation length and N)

• Scaling behaviour is observed in all the Co/Pd
  multilayers.
• Reasonable agreement with the TAB and KPZ models
  of film growth.
• Both approaches show that as the number of
  bilayer repeats increases, the interfaces become
  more two dimensional in character, as the Hurst
  fractal parameter h rises.

The in-plane Length Scale of the Conformal
Interface Roughness as a function of Bilayer
Repeat Number in Co/Pd Multilayers, submitted
to Journal of Physics D.
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Co/Pd multilayers(Relation between Keff and h)

• h?1 ? Higher Keff

The Relationship between Interface Structure,
Conformality and Perpendicular Anisotropy in
Co/Pd Multilayers, submitted to Journal of
Magnetism and Magnetic Materials.
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FWHM of 1st Bragg sheet for 15-bilayer Co/Ru
sample (MAR CCD data)
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Intensity of the first Bragg sheet for 15-bilayer
Co/Ru sample (MAR CCD data, integrated in qz)
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General Conclusions

• SR methods of determining h, ? , and ?.
• MAR CCD allows the data to be collected in very
  little time (but time consuming to analyse).

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Future Work (could be carried out at SESAME),
(using GIXR and GIXS techniques)

• Study of the magnetic multilayer thin films, spin
  valves, GMR devices in magnetic recording
  industry, Nano systems, Quantum dots, Lamellar
  structures, liquid surfaces, breast cancer,
• Theoretical models
• Computational modelling of the x-ray data

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SAXS Patterns from Different Breast Tissue Samples
Medical Applications of Synchrotron Radiation,
P. Suortti and W. Thomlinson, Phys. Med., Bio.,
48, (2003) R1
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Thank you for your attention