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Magnetism of Co overlayers and nanostructures on W(001): A first principles study
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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2008 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, Vol. 320, no 6, 1173-1179 p.Article in journal (Refereed) Published
Abstract [en]

The magnetic properties of Co nanostructures and a Co monolayer on W(001) have been studied in the framework of density functional theory. Different geometries such as planar and three-dimensional clusters have been considered, with cluster sizes varying between 2 and 13 atoms. The calculations were performed using the real-space linear muffin-tin orbital method (RS-LMTO-ASA). With respect to the stability of the magnetic state, we predict an antiferromagnetic (AFM) structure for the ground state of the planar Co clusters and a ferromagnetic (FM) state for the three-dimensional clusters. For the three-dimensional clusters, one of the AFM arrangements leads to frustration due to the competing FM and AFM exchange interactions between different atoms in the cluster, and gives rise to a non-collinear state with energy close to that of the FM ground state. The relative role of the Co-Co and Co-W exchange interactions is also investigated.

Place, publisher, year, edition, pages
2008. Vol. 320, no 6, 1173-1179 p.
Keyword [en]
density functional calculations, nanoclusters, metal-metal magnetic heterostructures
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-94301DOI: 10.1016/j.jmmm.2007.11.011ISI: 000254416300066OAI: oai:DiVA.org:uu-94301DiVA: diva2:168102
Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2012-03-26Bibliographically approved
In thesis
1. A Theoretical Study of Magnetism in Nanostructured Materials
Open this publication in new window or tab >>A Theoretical Study of Magnetism in Nanostructured Materials
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A first-principles linear scaling real-space method for investigating non-collinear magnetic behaviour of nanostructured materials has been developed. With this method, the magnetic structures of small supported transition metal clusters have been examined. The geometric constraints imposed on the clusters by the underlying surface is found to cause non-collinear behaviour for V, Cr, and Mn clusters on Cu(111). Fe clusters supported on Cu and Ni have been studied and both spin and orbital moments are found to be enhanced for the Fe atoms, which is attributed to the recuced symmetry present at the surface. Atoms in Co clusters have been found to order antiferromagnetically, and some times in a non-collinear fasion, when deposited on a W surface. Small clusters of fcc Fe embedded in Cu have been examined and a new type of ordering, not present in larger fcc Fe systems was found.

Several theoretical studies of Fe and Co based nanostructures consisting of multilayers or embedded clusters have been conducted, with the aim of predicting high moment materials for use in data storage applications. In agreement with previous experiments an enhancement of the magnetic moment is found compared to the magnetic moment of bcc Fe. The enhancement has been shown to be caused by increased spin moments for Fe atoms in close proximity with Co atoms, and this enhancement depends on the number of Co neighbours. As a result of these studies, a possible method of increasing the magnetic moment of cluster based materials has been proposed.

Fermi surface analysis have been performed both on bulk materials, in order to investigate mechanisms for stabilizing non-collinear magnetic states, and in layered structures where the effect of the Fermi surface on the interlayer exchange coupling has been investigated.

In addition to the development of a real-space electronic structure method for non-collinear magnetism, a density matrix purification method has been implemented in the framework of linear muffin-tin orbitals.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. x + 78 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 167
Keyword
Physics, magnetism, clusters, non-collinear, multilayers, first-principles theory, electronic structure, high-moment materials, exchange interactions, linear scaling methods, Fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-6763 (URN)91-554-6527-7 (ISBN)
Public defence
2006-05-05, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
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Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2012-03-27Bibliographically approved

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Bergman, AndersNordström, LarsEriksson, Olle

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