liu.seSearch for publications in DiVA
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Magnetism in systems with reduced dimensionality and chemical disorder: the local environment effects
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
Theoretical Physics Department, Moscov Steel and Alloys Institute, Moscow, Russia.
2006 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 300, no 1, 211-215 p.Article in journal (Refereed) Published
Abstract [en]

We study influence of the local chemical environment, the so-called local environment effects, on the electronic structure and properties of magnetic systems with reduced dimensionality and chemical disorder, and show that they play a crucial role in a vicinity of magnetic instability. As a model, we consider Fe–Ni Invar. We present results obtained from ab initio calculations of the electronic structure, magnetic moments, and exchange interactions in random fcc Fe–Ni alloy, for a single monolayer alloy film on a Cu (0 0 1) substrate as well as in the bulk. We analyze the difference between the film and the bulk magnetization, which is found to be most pronounced for dilute alloys. We also analyze a sensitivity of the individual magnetic moments and effective exchange parameters to the local chemical environment of the atoms.

Place, publisher, year, edition, pages
Elsevier , 2006. Vol. 300, no 1, 211-215 p.
Keyword [en]
Local environment effects, Invar alloys, First-principles calculations
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-17428DOI: 10.1016/j.jmmm.2005.10.065OAI: oai:DiVA.org:liu-17428DiVA: diva2:209237
Available from: 2009-03-24 Created: 2009-03-24 Last updated: 2017-12-13
In thesis
1. Thermal Expansion and Local Environment Effects in Ferromagnetic Iron-Based Alloys: A Theoretical Study
Open this publication in new window or tab >>Thermal Expansion and Local Environment Effects in Ferromagnetic Iron-Based Alloys: A Theoretical Study
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Nobel Prize for Physics 1920 was awarded to C.-E. Guillaume for his discovery of properties of nickel steels. He had previously observed that certain iron-nickel alloys exhibit the Invar effect i.e. an extremely low thermal expansion coefficient over a wide range of temperature. The decades since then have seen the observation of similar phenomena in other iron-based materials such as iron-platinum and iron-palladium. Moreover, there has been a great deal of theoretical work on the mechanism behind the Invar anomaly in the above-mentioned systems. However, despite many years of intensive research, a widely accepted microscopic theory of the effects is still lacking.

The present thesis aims at providing an insight into the physical nature of the thermal expansion of ferromagnetic random face-centered cubic iron-nickel, ironplatinum and iron-palladium bulk solids.

First, the thermal expansion coefficient is modeled as a function of temperature. The theory relies on the disordered local moment (DLM) formalism. However, contrary to all the previous models, the mapping between equilibrium states and partially disordered local moment (PDLM) states involves the probability that an iron-iron nearest-neighbour pair shows anti-parallel local magnetic moments, and the average lattice constant of the system at a finite temperature is calculated by minimization of an energy. The approach is applied to iron-nickel alloys. The model qualitatively reproduces several experimentally observed properties of disordered fcc iron-nickel solids. This includes Guillaume’s famous plot of the thermal expansion coefficient at room temperature as a function of concentration.

Second, for the purpose of studying the origin of the anomalous expansion, the anomalous and normal contributions to the thermal expansion coefficient are defined, then evaluated for iron-nickel alloys. The results support the idea that the peculiar behaviour of the expansivity, , originates solely from the anomalous contribution,αa.

Subsequently, the anomalous contribution is modeled for iron-nickel systems. In formulating the model, the following observation is taken into account; the average lattice spacing of an Fe100−xNix alloy at temperature T in a partially disordered local moment state is strongly negatively correlated with the probability that a nearest-neighbour pair has each of its two sites occupied by an iron atom and exhibits anti-ferromagnetically aligned magnetic moments (XFFAP). The quantity αa(x, T ) is estimated for several couples of values of the parameters x and T . Model results are found to agree qualitatively and quantitatively well with data obtained from the definition of αa. Thus, the model can successfully explain the basic process leading to the anomalous thermal expansion. It is consistent with the theory that the coefficient αa is controlled by the temperature derivative of XFFAP. Finally, the anomalous contribution to the thermal expansion coefficient of Fe72Pt28 and Fe66Pd34 solids is modeled as that of Fe65Ni35. A good agreement between the model results and experimental data for the expansivity as a function of temperature is noted. In conclusion, the Invar effects in disordered fcc iron-nickel, iron-platinum and iron-palladium alloys may have a common origin.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 49 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1245
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-17433 (URN)978-91-7393-682-8 (ISBN)
Public defence
2009-04-03, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2009-03-24 Created: 2009-03-24 Last updated: 2009-03-24Bibliographically approved
2. Theoretical Considerations of Local Environment Effects in Alloys
Open this publication in new window or tab >>Theoretical Considerations of Local Environment Effects in Alloys
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is devoted to a theoretical study of local environment effects in alloys. A fundamental property of a disordered system is that all chemically equivalent atoms are different due to their different chemical environments, in contrast to an ideal periodic solid where all the atoms that occupy equivalent positions in the crystal have exactly the same physical properties. The local environment effects have been largely ignored in earlier theories of disordered systems, that is the system has been treated as a whole and average properties have been derived. Moreover, inhomogeneous systems, such as surfaces and interfaces, induce local environment effects that are not necessarily present in the bulk.

The importance and presence of local environment effects are illustrated by calculating observable physical properties in various systems. In particular, by employing the complete screening picture the effects of local environments on the core-level binding energy shifts as well as Auger shifts in random alloys are in- vestigated. This so-called disorder broadening effect has recently been observed experimentally. It is shown that there are different contributions to the disorder broadening that vary with the local chemical environment. Furthermore, the influ- ence of inhomogeneous lattice distortions on the disorder broadening of the core- level photoemission spectra are considered for systems with large size-mismatch between the alloy components.

The effects of local chemical environments on physical properties in magnetic systems are illuminated. A noticeable variation in the electronic structure, local magnetic moments and exchange parameters at different sites is obtained. This reflects the sensitivity to different chemical environments and it is shown to be of qualitative importance in the vicinity of magnetic instability.

The local environment effects due to the presence of surfaces and interfaces are also considered. The effect is explicitly studied by considering the concentration profile of a thin Ag-Pd film deposited on a Ru substrate. Two computational approaches are utilized to calculate the relative composition in each layer of the thin film as a function of temperature in a theoretically consistent way. It is shown that, opposed to the situation in the bulk, where a complete solubility between Ag and Pd takes place, a non-uniform distribution of the alloy components across the film is observed.

In another study it is investigated whether the presence of TiN interfaces changes the dynamical and thermodynamic stability of B1 SiN. Phonon calcula- tions show that TiN interfaces have a stabilization effect on the lattice dynamics. On the other hand, calculations of the Si vacancy formation energy show that the structures are unstable with respect to composition variations.

 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 86 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1353
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-63443 (URN)978-91-7393-285-1 (ISBN)
Public defence
2010-12-17, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2010-12-27 Created: 2010-12-19 Last updated: 2010-12-27Bibliographically approved
3. First-principles study of spin-flip transition in Fe-Ni invar alloys
Open this publication in new window or tab >>First-principles study of spin-flip transition in Fe-Ni invar alloys
2006 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

More than a hundred years ago, Guillaume discovered that the alloy Fe65Ni35, at equilibrium under normal pressure, was invar. Indeed, its thermal expansion coefficient was anomalously small over a wide temperature interval. It is now known that the invar effect in this alloy is related to magnetism.

Recently, the ground state spin configuration was computed using spin-density functional theory and supercell methods. According to these calculations, the ground state spin configuration was ferromagnetic at atomic volumes bigger than a specific critical atomic volume. At the critical atomic volume, a few spins flipped. The aim of this licenciate project was to study the spin-flip transition which happens in the random fcc Fe50Ni50, using computer codes based on spin-density functional theory and supercell methods.

During the first part of the project, I characterized the chemical environment of the Fe sites where the spins flipped. These sites were in an Fe-rich environment. I computed the effective exchange parameters of the classical Heisenberg hamiltonian of the random fcc Fe50Ni50. The sign of the effective exchange parameter at any site where a spin flipped changed at the critical atomic volume, whereas the sign of the exchange parameter at any other site remained constant. The dispersion in the effective exchange parameters increased, as the atomic volume decreased from a specific atomic volume towards the critical atomic volume.

In the second part of the project, I computed the relaxed ionic positions. For any type of bond, the dispersion in the nearest neighbour bond length was much bigger than the change, due to the ionic positions relaxation, in the average value of the nearest neighbour bond length. Also, I investigated the effect of the ionic positions relaxation on the local magnetic moments. This effect was found to be relatively small.

After I found these results, I wondered what the effect of the ionic positions relaxation on the dispersion of the effective exchange parameters was and if the change of the dispersion in the effective exchange parameters with the atomic volume could provide an explanation for the invar effect in Fe-Ni invar alloys.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2006. 32 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1232
Series
LIU-TEK-LIC, 13
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-33066 (URN)19031 (Local ID)91-85497-25-8 (ISBN)19031 (Archive number)19031 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-11-25

Open Access in DiVA

No full text

Other links

Publisher's full textLink to Ph.D. Thesis

Authority records BETA

Abrikosov, IgorLiot, FrancoisMarten, Tobias

Search in DiVA

By author/editor
Abrikosov, IgorLiot, FrancoisMarten, Tobias
By organisation
Theoretical PhysicsThe Institute of Technology
In the same journal
Journal of Magnetism and Magnetic Materials
Natural Sciences

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 308 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf