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A neutron powder diffraction study of the helimagnetic structure of TlCo2Se2−xSx
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
2010 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, Vol. 322, no 6, 681-685 p.Article in journal (Refereed) Published
Abstract [en]

The magneti clayer structure of TlCo2Se2-xSx has been thoroughly re-investigated with neutron powder diffraction. The cobalt magnetic moments are ferromagnetically arranged with in the layers, but the interlayer coupling differs profoundly with varying composition (x): the spins in TlCo2Se2 form a helix along the c-axis with a turning-angle of similar to 119 degrees at 1.4 K. This kind of helical structure prevails for 0 <= x <= 1.5 with a gradual decrease of the angle with increasing sulphur content, down to 34 degrees, showing an almost linear relationship with the interlayer distance of Co-Co. For x >= 1.75 the interlayer couplingchanges to ferromagnetic. Unexpectedly, two helices were found to coexist at x = 0.5 and x = 1.0. The interaction between adjacent cobalt layers is there characterized by an incommensurate angle (106 degrees, resp., 73 degrees) together with a commensurate angle of 90 degrees. The magnetic structures have been refined as two magnetic phases, each having a characteristic wave vector. A tentative model where the symmetry of the structure and the interlayer distance compete is considered for explaining the simultaneous occurrence of the two kinds of diffraction profile satellites.

Place, publisher, year, edition, pages
2010. Vol. 322, no 6, 681-685 p.
Keyword [en]
Layered magnetic structure; ThCr2Si2 type; Coexisting magnetic helix; TlCo2S2; TlCo2Se2
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-93543DOI: 10.1016/j.jmmm.2009.10.040ISI: 000273434300022OAI: oai:DiVA.org:uu-93543DiVA: diva2:167051
Available from: 2005-10-07 Created: 2005-10-07 Last updated: 2011-03-28Bibliographically approved
In thesis
1. Chemical Tuning of the Magnetic Interactions in Layer Structures
Open this publication in new window or tab >>Chemical Tuning of the Magnetic Interactions in Layer Structures
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Thin metal films have found their use in many magnetic devices. They form pseudo two-dimensional systems, where the mechanisms for the magnetic interactions between the layers are not completely understood. Layered crystal structures have an advantage over such artificial systems, since the layers can be strictly mono-atomic without any unwanted admixture. In this study, some model systems of layered magnetic crystal structures and their solid solutions have been investigated by x-ray and neutron diffraction, Mössbauer and electron spectroscopy, heat-capacity and magnetic measurements, and first-principle electronic structure calculations, with the goal of deepening our understanding through controlled chemical synthesis.

The compounds TlCo2S2, TlCo2Se2 and their solid solution TlCo2Se2-xSx, all containing well separated cobalt atom sheets, order with the moments ferromagnetically aligned within the sheets. In TlCo2S2, the net result is ferromagnetism, while TlCo2Se2 exhibits antiferromagnetism. The inter-layer distance is crucial for the long-range coupling, and it was varied systematically through Se-S substitution. The incommensurate helical magnetic structure found for TlCo2Se2 (x = 0) prevails in the composition range 0 ≤ x ≤ 1.5 but the pitch of the helix changes. The accompanying reduction in inter-layer distance on sulphur substitution varies almost linearly with the coupling angle of the helix. An additional competing commensurate helix (90°) appears in the medium composition range (found for x = 0.5 and 1.0).

The systems TlCo2-xMexSe2 show helical magnetic ordering for Me = Fe or Cu, while a collinear antiferromagnetic structure occurs for Me = Ni. Magnetic order is created by iron substitution for copper in the Pauli paramagnetic TlCu2Se2, but now with the moments perpendicular to the metal sheets.

TlCrTe2 forms a quite different crystal structure, with intra-layer ferromagnetic alignment and net collinear antiferromagnetism. In contrast to the other phases, the values of the moments conform well to a localised model for Cr3+.

Place, publisher, year, edition, pages
Uppsala: Institutionen för materialkemi, 2005. 63 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 97
Keyword
Inorganic chemistry, neutron powder diffraction, magnetometry, layered magnetic structure, incommensurate helical structure, ThCr2Si2 type structure, antiferromagnetism, ferromagnetism, electronic structure calculations, Oorganisk kemi
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-5973 (URN)91-554-6357-6 (ISBN)
Public defence
2005-10-28, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2005-10-07 Created: 2005-10-07 Last updated: 2013-09-13Bibliographically approved

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