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Longitudinal spin fluctuations of thermal and magnetic properties of TlCo2Se2-xSx
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
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2004 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, Vol. 281, no 2-3, 388-393 p.Article in journal (Refereed) Published
Abstract [en]

At isovalent substitution of Se for S, the layered chalcogenides TlCo2Se2−xSx (0⩽x⩽2) exhibit a change of magnetic order type, from an antiferromagnetic helix at low S content to a ferromagnet at high S content. The effective magnetic moments peff∼2 μB per Co, as estimated from the magnetic susceptibility at high temperatures, significantly exceed what would be the result of the Co magnetic moments μsat∼0.5 μB in both the ferromagnetic and antiferromagnetic phases. This signifies the crucial role of longitudinal spin fluctuations in the magnetic behaviour of these conducting compounds. The spin fluctuations reveal themselves also in specific heat measurements, leading to a diminution of the expected anomalies at the Curie/Néel temperatures and to an excess of heat capacity at high temperatures as compared to phonon contributions.

Place, publisher, year, edition, pages
2004. Vol. 281, no 2-3, 388-393 p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-93541DOI: 10.1016/j.jmmm.2004.05.002OAI: oai:DiVA.org:uu-93541DiVA: diva2:167049
Available from: 2005-10-07 Created: 2005-10-07 Last updated: 2015-09-14Bibliographically 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.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 97
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
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
Available from: 2005-10-07 Created: 2005-10-07 Last updated: 2013-09-13Bibliographically approved

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Berger, Rolf
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