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Magnetism and Structure of Thin 3d Transition Metal Films: XMCD and EXAFS using Polarized Soft X-Rays
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this Thesis the magnetic and structural properties of thin epitaxial Fe, Co, and Ni films are discussed. Some of the in-situ prepared samples were used to characterize the degree of circular polarization of the newly installed beamline D1011 at MAX-lab. By means of x-ray magnetic circular dichroism (XMCD) and utilizing the associated magneto optic sum rules, the orbital (ml) and spin (ms) moments are determined directly in mB/atom with elemental specificity. The extended x-ray absorption fine structure (EXAFS) measurements yield site specific information on the local crystallographic structure.

These measurements were performed using the circular x-rays of several beamlines. The influence of the degree of spatial source coherence lspat of the x-rays was characterized by means of Fresnel diffractometry. A correlation between enhanced XAS white line intensities and higher values of lspat was established for 20 ML Fe, Co, and Ni films on Cu(100).

The degree of circularly polarized x-rays (Pc) at beamline D1011 at MAX-lab was characterized by studying Fe films on Cu(100) by means of XMCD. The maximum value of Pc is experimentally determined to Pc =0.85.

The Au/Co/Au trilayer system was studied as a function of Co thickness, temperature, and Au cap thickness. A 10 mono-layer (ML) Co film, with an Au cap of 20 Å, shows a spin reorientation transition (SRT) from an in-plane to an out-of-plane easy direction as the temperature is lowered from 300 K to 200 K. The magnetic properities of these Co films are very different to what is found for bulk samples due to, in particular, the broken symmetry at the interfaces.

The thickness dependent spin reorientation transition in the Fe/Ag(100) system was characterized by means of XMCD and EXAFS measurements. 3 ML Fe films show an out-of-plane easy direction with an 125% enhanced orbital moment as compared to the 25 ML Fe in-plane film. Simulations of the Fe L-edge EXAFS indicate the bulk Fe bcc structure for film thicknesses of 6-25 ML Fe. For 3 ML Fe strong deviations from this bcc phase is observed.

Ultrathin Co films deposited on flat and vicinal Cu(111) in the thickness region 1-25 ML were studied by means of XMCD and scanning tunneling microscopy (STM). The vicinal Cu(111) Co deposition leads to the formation of elongated islands preferentially oriented along the step edges. In connection to this particular Co growth mode we observe an increase of both the orbital and the spin moment on the vicinal Cu(111) of about 25% relative to what was observed for Co on flat Cu(111).

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2003. , p. 64
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 840
Keyword [en]
Physics, thin film, xmcd, exafs, anisotropy, coherence, circular polarization, magnetism, Fe, Co, Ag
Keyword [sv]
Fysik
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:uu:diva-3407ISBN: 91-554-5632-4 (print)OAI: oai:DiVA.org:uu-3407DiVA, id: diva2:162702
Public defence
Polhemsalen, Ångströmlaboratoriet, Uppsala
Opponent
Supervisors
Available from: 2003-04-29 Created: 2003-04-29 Last updated: 2013-07-05Bibliographically approved
List of papers
1. A comparative study of x-ray absorption spectroscopy at various synchrotron facilities and the effect of transverse source coherence
Open this publication in new window or tab >>A comparative study of x-ray absorption spectroscopy at various synchrotron facilities and the effect of transverse source coherence
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2000 In: Journal of Electron Spectroscopy and Related Phenomenas, Vol. 113, p. 67-77Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90364 (URN)
Available from: 2003-04-29 Created: 2003-04-29Bibliographically approved
2. Magnetic x-ray circular dichroism on in situ grown 3d magnetic thin films on surfaces
Open this publication in new window or tab >>Magnetic x-ray circular dichroism on in situ grown 3d magnetic thin films on surfaces
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2001 (English)In: Journal of Synchrotron Radiation, Vol. 8, p. 120-125Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-90365 (URN)
Available from: 2003-04-29 Created: 2003-04-29 Last updated: 2012-03-15Bibliographically approved
3. Quantitative analysis of L-edge white line intensities: the influence of saturation and transverse coherence
Open this publication in new window or tab >>Quantitative analysis of L-edge white line intensities: the influence of saturation and transverse coherence
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2001 (English)In: Journal of Synchrotron Radiation, Vol. 8, p. 437-439Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-90366 (URN)
Available from: 2003-04-29 Created: 2003-04-29 Last updated: 2012-03-15Bibliographically approved
4. A circularly polarized x-ray study of the temperature-dependent spin-reorientation transition of thin Co films
Open this publication in new window or tab >>A circularly polarized x-ray study of the temperature-dependent spin-reorientation transition of thin Co films
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2001 In: Journal of Magnetism and Magnetic Materials, Vol. 226-230, p. 1675-1677Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90367 (URN)
Available from: 2003-04-29 Created: 2003-04-29Bibliographically approved
5. Cap layer influence on the spin reorientation transition in Au/Co/Au
Open this publication in new window or tab >>Cap layer influence on the spin reorientation transition in Au/Co/Au
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2002 In: Physical Review B: Condensed Matter and Materials Physics, Vol. 66, p. 172401-04Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90368 (URN)
Available from: 2003-04-29 Created: 2003-04-29Bibliographically approved
6. Ultrathin Co films on flat and vicinal Cu(111) surfaces: Determination of per atom orbital and spin moments
Open this publication in new window or tab >>Ultrathin Co films on flat and vicinal Cu(111) surfaces: Determination of per atom orbital and spin moments
2002 In: Journal of Applied Physics, Vol. 91, p. 6881-83Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90369 (URN)
Available from: 2003-04-29 Created: 2003-04-29Bibliographically approved
7. Structure and magnetism on in-situ ultrathin epitaxial films: XMCD and EXAFS on Fe/Ag(100)
Open this publication in new window or tab >>Structure and magnetism on in-situ ultrathin epitaxial films: XMCD and EXAFS on Fe/Ag(100)
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2003 (English)In: Proceedings of the 7th International Conference on Nanometer-Scale Science and Technology and the 21st European Conference on Surface Science, 2003, Vol. 532-535, p. 76-81Conference paper, Published paper (Refereed)
Abstract [en]

We have made in situ investigations of epitaxial ultrathin Fe films on Ag(1 0 0). This system is known to exhibit a reorientation of the magnetization, dependent of Fe thickness and temperature. Our aim here is to correlate the local structure with the magnetic properties of this system. The X-ray absorption fine structure has been recorded in situ both in the near edge as well as in the extended X-ray absorption fine structure (EXAFS) range. Using X-ray magnetic circular dichroism we find that, below 300 K, films between 2 and 6 monolayers show an out-of-plane remanent magnetization whereas for thicker films the magnetization lies in-plane. By making use of the Fe L-edge EXAFS we obtain information on the local structure around the Fe atoms, such as the interatomic distances, the coordination number, and the mean square relative displacement of the first neighbor shells.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-90370 (URN)10.1016/S0039-6028(03)00112-2 (DOI)
Conference
7th International Conference on Nanometer-Scale Science and Technology and the 21st European Conference on Surface Science, 24-28 June, 2002, Malmo, Sweden
Available from: 2003-04-29 Created: 2003-04-29 Last updated: 2013-09-18Bibliographically approved
8. Ultrathin Co films on flat and vicinal Cu(111) surfaces: per atom determination of orbital and spin moments
Open this publication in new window or tab >>Ultrathin Co films on flat and vicinal Cu(111) surfaces: per atom determination of orbital and spin moments
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Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90371 (URN)
Available from: 2003-04-29 Created: 2003-04-29Bibliographically approved
9. The temperature-driven transition to perpendicular magnetization in a Co film studied by XMCD and XRMS based magnetometry
Open this publication in new window or tab >>The temperature-driven transition to perpendicular magnetization in a Co film studied by XMCD and XRMS based magnetometry
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Manuscript (Other academic)
Identifiers
urn:nbn:se:uu:diva-90372 (URN)
Available from: 2003-04-29 Created: 2003-04-29 Last updated: 2010-01-13Bibliographically approved
10. Structure and magnetism for ultra-thin epitaxial Fe on Ag(100)
Open this publication in new window or tab >>Structure and magnetism for ultra-thin epitaxial Fe on Ag(100)
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2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 13, p. 134423-Article in journal (Refereed) Published
Abstract [en]

We have made in-situ investigations of ultrathin films of Fe grown on a Ag(100) single crystal. This system is known to exhibit a reorientation of the magnetization, dependent on both Fe thickness and temperature. X-ray absorption fine structure has been recorded for samples prepared in-situ, both in the near edge and in the extended x-ray absorption fine structure (EXAFS) region. Using x-ray magnetic circular dichroism we found that Fe films between 2–5 monolayers show an out-of-plane remanent magnetization. For thicker films the magnetization lies in-plane. By applying the magneto-optical sum rules we found an enhancement of the orbital moment (ml) for the out-of-plane phase, whereas the spin moment (ms) is unchanged. From the Fe L-edge EXAFS, we obtain information on the local crystallographic structure. A strong correlation between the local crystallographic structure and the magnetic properties is found for the Fe∕Ag(100) system. Variations in the nearest neighbor distance of ∼0.15 Å are observed when comparing 3 ML and 25 ML films. By comparison to simulations performed with the FEFF 8.10 code, we can identify a bcc structure for 6–25 ML Fe on Ag(100). For the 3 ML Fe film our simulations indicate strong deviations from any structure derived along the Bain path. We conclude that intermixing and distortion are important to describe the structure in this thickness range.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-94434 (URN)10.1103/PhysRevB.73.134423 (DOI)
Available from: 2006-05-03 Created: 2006-05-03 Last updated: 2017-12-14Bibliographically approved
11. Elliptically polarized soft x-rays produced using a local bump in MAX II - Characterization of the degree of polarization
Open this publication in new window or tab >>Elliptically polarized soft x-rays produced using a local bump in MAX II - Characterization of the degree of polarization
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Manuscript (Other academic)
Identifiers
urn:nbn:se:uu:diva-90374 (URN)
Available from: 2003-04-29 Created: 2003-04-29 Last updated: 2010-01-13Bibliographically approved

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