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Magnetic short-range order in the new ternary phase Mn8Pd15Si7
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
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2005 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, Vol. 403, no 1-2, 19-28 p.Article in journal (Refereed) Published
Abstract [en]

A new compound, Mn8Pd15Si7, is reported to crystallize in a face centered cubic unit cell of dimension a = 12.0141(2) Å, space group, and can thus be classified as a G-phase. The crystal structure was studied by single crystal X-ray diffraction, X-ray and neutron powder diffraction and electron diffraction. A filled Mg6Cu16Si7 type structure was found, corresponding to the Sc11Ir4 type structure. The magnetic properties were investigated by magnetization measurements and Reverse Monte Carlo modeling of low temperature magnetic short-range order (SRO). Dominating near neighbor antiferromagnetic correlations were found between the Mn atoms and geometric frustration in combination with random magnetic interactions via metal sites with partial Mn occupancy were suggested to hinder formation of long-range magnetic order.

Place, publisher, year, edition, pages
2005. Vol. 403, no 1-2, 19-28 p.
Keyword [en]
Intermetallics, Neutron powder diffraction, X-ray diffraction, Magnetic measurements
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-93495DOI: 10.1016/j.jallcom.2005.04.202OAI: oai:DiVA.org:uu-93495DiVA: diva2:166986
Available from: 2005-09-22 Created: 2005-09-22 Last updated: 2013-05-29Bibliographically approved
In thesis
1. Tunable Magnetic Properties of Transition Metal Compounds
Open this publication in new window or tab >>Tunable Magnetic Properties of Transition Metal Compounds
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The magnetic properties of transition metal compounds have been studied using SQUID-magnetometry, magnetic force microscopy and Lorentz transmission electron microscopy. New magnetic materials have been found and their magnetic properties have been determined. How the magnetic properties of a material can be changed through e.g. chemical substitution of magnetic and nonmagnetic atoms and shape and size effects have also been studied. Three different sets of samples have been investigated: three new Mn-compounds, two substitution series of layered magnetic structures and ferromagnetic micronsized thin film elements.

The three Mn-compounds, Mn3IrSi, IrMnSi and Mn8Pd15Si7, show different magnetic ordering. Mn3IrSi orders 'antiferromagnetically' at 210 K. IrMnSi forms a double cycloidal spin spiral below 460 K. Mn8Pd15Si7 only shows short-range magnetic ordering.

Substituting Se with S in TlCo2Se2-xSx changes the magnetic order from a spin spiral to a colinear ferromagnet for a composition of x=1.75. An intermediate region exists where the compound is neither a pure ferromagnet, nor purely a spin spiral, as evidenced by the magnetization versus field measurements for the x=1.3 and 1.5 samples. This is also seen in the temperature dependent susceptibility measurements. For the TlCu2-xFexSe2 compounds it was found that the ordering temperature and saturation magnetic moment per Fe-atom changed with composition x.

Ferromagnetic micronsized thin film elements in permalloy, Fe20Ni80, and epitaxial Fe/Co multilayers were studied. For the Fe/Co multilayer thin film elements it was found that it is possible to change the magnetization reversal process, by aligning the easy shape anisotropy axis with either the easy or the hard magnetocrystalline anisotropy axis. In the permalloy elements the effect of inter-elemental distance was found to determine the interval of fields where multidomain states were stable, so that for shorter inter-elemental distances multidomain states were stable for a shorter interval of fields. The domain structure of permalloy elements in rotating magnetic fields was also studied. Higher applied fields led to a broader interval of angles in which saturated states were stable.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. viii, 58 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 95
Keyword
Magnetic properties, Transition metal compounds, Magnetic structure, Domain structure, SQUID-magnetometry, MFM
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-5939 (URN)91-554-6346 (ISBN)
Public defence
2005-10-14, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00
Opponent
Supervisors
Available from: 2005-09-22 Created: 2005-09-22 Last updated: 2015-09-14Bibliographically approved
2. The Structural Basis for Magnetic Order in New Manganese Compounds
Open this publication in new window or tab >>The Structural Basis for Magnetic Order in New Manganese Compounds
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Materials with new or improved properties are crucial for technological development. To provide the foundation for future successful products, it is important to prepare and characterise new chemical compounds that could show unusual properties. The properties of magnetic materials are closely related to their crystal, magnetic and electronic structures. This thesis focuses on the novel synthesis and structural characterisation of a number of new ternary or pseudo-ternary silicides and germanides of manganese with iridium, cobalt or palladium. To provide a more complete picture of the complex magnetic properties, crystal and magnetic structure refinements by the Rietveld method of X-ray and neutron powder diffraction data are complemented by single-crystal X-ray diffraction, electron diffraction, magnetisation measurements and Reverse Monte Carlo simulations of magnetic short-range order. The experimental results are corroborated by first-principles electronic structure and total energy calculations.

A commensurate non-collinear antiferromagnetic structure is found for most compounds of the solid solution Mn3Ir1-yCoySi1-xGex. The non-collinearity is a result of geometric frustration in a crystal structure with magnetic Mn atoms located on a three-dimensional network of triangles. The close structural similarity to the β-modification of elemental manganese, which does not order magnetically, inspired a closer theoretical comparison of the Mn3Ir1-yCoySi1-xGex propertieswith β-Mn.

Magnetic frustration is also observed for Mn4Ir7-xMnxGe6, and is an important factor underlying the dramatic change from commensurate antiferromagnetic order to spin glass properties induced by a small variation in Mn concentration. Magnetic short-range order with dominant antiferromagnetic correlation is observed for Mn8Pd15Si7, and results from a random distribution of Mn atoms in-between the geometrically frustrated magnetic moments on the Mn octahedra.

An incommensurate cycloidal magnetic structure, observed for IrMnSi, is stabilised by an electronic structure effect, which also accounts for the non-collinearity of the Mn3IrSi type magnetic structure.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. 65 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 42
Keyword
Inorganic chemistry, Crystal structure, Magnetic structure, Manganese compounds, Transition metal silicides, Transition metal germanides, Magnetic frustration, Neutron powder diffraction, X-ray diffraction, Magnetisation measurements, DFT, Oorganisk kemi
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-5746 (URN)91-554-6215-4 (ISBN)
Public defence
2005-05-12, Häggsalen, The Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2005-04-19 Created: 2005-04-19 Last updated: 2013-06-20Bibliographically approved

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Eriksson, ThereseNordblad, PerGustafsson, TorbjörnAndersson, Yvonne

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