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Structure and magnetism on in-situ ultrathin epitaxial films: XMCD and EXAFS on Fe/Ag(100)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
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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, 76-81 p.Conference 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.

Place, publisher, year, edition, pages
2003. Vol. 532-535, 76-81 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-90370DOI: 10.1016/S0039-6028(03)00112-2OAI: oai:DiVA.org:uu-90370DiVA: diva2:162697
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
In thesis
1. Magnetism and Structure of Thin 3d Transition Metal Films: XMCD and EXAFS using Polarized Soft X-Rays
Open this publication in new window or tab >>Magnetism and Structure of Thin 3d Transition Metal Films: XMCD and EXAFS using Polarized Soft X-Rays
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. 64 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 840
Keyword
Physics, thin film, xmcd, exafs, anisotropy, coherence, circular polarization, magnetism, Fe, Co, Ag, Fysik
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-3407 (URN)91-554-5632-4 (ISBN)
Public defence
Polhemsalen, Ångströmlaboratoriet, Uppsala
Opponent
Supervisors
Available from: 2003-04-29 Created: 2003-04-29 Last updated: 2013-07-05Bibliographically approved
2. Exploring the Magnetism of Ultra Thin 3d Transition Metal Films
Open this publication in new window or tab >>Exploring the Magnetism of Ultra Thin 3d Transition Metal Films
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis the magnetic and structural properties of ultra-thin 3d transition metals films have been investigated, in particular Fe, Ni and Co films. X-ray Magnetic Circular Dichroism (XMCD) has provided element specific spin (ms ) and orbital (ml ) moments per atom by utilizing the magneto optic sum-rules. Element specific hysteresis curves have been measured by means of X-ray Resonant Magnetic Scattering (XRMS), and the local crystallographic structure has been investigated using Extended X-ray Absorption Fine Structure (EXAFS).

By performing XMCD on Fe/Ag(100) we observe a spin reorientation from in-plane to out-of-plane as the Fe thickness is lowered. At temperatures below 300K it occurs around 5-7 mono layers (ML) of Fe. While reorienting the magnetization out-of-plane the orbital moment increases with 125% but only a minor increase (5%) of the spin moment is observed. Extended X-ray Absorption Fine Structure (EXAFS) measurements indicate that films 6 ML and thicker have a bulk-like bcc structure. For the thin out-of-plane films, the local crystallographic structure is more complicated.

The spin reorientation of the Au/Co/Au tri-layer system has been studied as a function of temperature, Co layer and Au cap thickness. An unexpected behavior of the orbital moment upon spin reorientation is found in these systems. An ex-situ prepared sample shows a smooth spin reorientation from an in-plane to an out-of-plane easy magnetization direction as the temperature is lowered from 300K to 200K. In-situ prepared samples have also been investigated and a novel phase diagram has been identified. The Au/Co interface has been explored during the Au capping by means of photoemission measurements.

In the bi- and tri-layer system of Fe and Ni we have been able to manipulate the spin reorientation by varying the Fe and Ni thickness. A novel non-collinear interlayer exchange interaction for 3d ferro magnets in direct contact has been discovered for a set of samples. This exchange interaction is found to be strongly dependant on the preparation conditions.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. v + 47 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 175
Keyword
Physics, thin film, xmcd, xrms, exafs, anisotropy, magnetism, Fe, Ni, Co, Ag, Cu, Fysik
Identifiers
urn:nbn:se:uu:diva-6836 (URN)91-554-6554-4 (ISBN)
Public defence
2006-05-24, Polhemsalen, Ångströmlabratoriet, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2006-05-03 Created: 2006-05-03 Last updated: 2013-09-18Bibliographically approved

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Karis, OlofArvanitis, Dimitri

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