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Structure-Magnetism Relations in Selected Iron-based Alloys: A New Base for Rare Earth Free Magnetic Materials
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.ORCID iD: 0000-0003-0336-2560
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Materials for energy applications are of great importance for a sustainable future society. Among these, stronger, lighter and more efficient magnetic materials will be able to aid mankind in many applications for energy conversion, for example generators for energy production, electric vehicles and magnetic refrigerators. Another requirement for the materials is that they should be made from cheap and abundant elements. For these reasons temperature induced magnetic transitions for three materials were studied in this work; one for permanent magnet applications and two magnetocaloric materials.

Fe5SiB2 has a high Curie temperature and orders ferromagnetically at 760 K, providing possible application as a permanent magnet material. The ordering of the magnetic moments were studied and found to be aligned along the tetragonal c-axis and Fe5SiB2 undergoes a spin transition on cooling through a transition temperature (172 K), where the spins reorient along the a-axis in an easy plane.

AlFe2B2 orders ferromagnetically at 285 K, making it a candidate for the active material in a magnetic refrigerator. The order of the magnetic transition has been studied as well as the magnetic structure. It was found that the magnetic moments are aligned along the crystallographic a-axis and that the magnetic transition is of second order.

FeMnP0.75Si0.25 undergoes a first order magnetic transition around 200 K and the transition temperatures on cooling are different for the first cooling/heating cycle than for following cycles. This so called ”virgin effect” has been studied and found to originate from an irreversible structure change on the first cooling cycle through the ferromagnetic transition temperature.

Place, publisher, year, edition, pages
Uppsala: Kph Trycksaksbolaget: Kph , 2015. , 47 p.
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-267575OAI: oai:DiVA.org:uu-267575DiVA: diva2:873648
Presentation
2015-12-17, 09:15 (English)
Opponent
Supervisors
Available from: 2015-12-02 Created: 2015-11-24 Last updated: 2015-12-02Bibliographically approved
List of papers
1. Magnetostructural transition in Fe5SiB2 observed with neutron diffraction
Open this publication in new window or tab >>Magnetostructural transition in Fe5SiB2 observed with neutron diffraction
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2016 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 235, 113-118 p.Article in journal (Refereed) Published
Abstract [en]

The crystal and magnetic structure of Fe5SiB2 has been studied by a combination of X-ray and neutron diffraction. Also, the magnetocrystalline anisotropy energy constant has been estimated from magnetisation measurements. High quality samples have been prepared using high temperature synthesis and subsequent heat treatment protocols. The crystal structure is tetragonal within the space group I4/mcm and the compound behaves ferromagnetically with a Curie temperature of 760 K. At 172 K a spin reorientation occurs in the compound and the magnetic moments go from aligning along the c-axis (high T) down to the ab-plane (low T). The magnetocrystalline anisotropy energy constant has been estimated to 03 MJ/m(3) at 300 K.

National Category
Inorganic Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-267572 (URN)10.1016/j.jssc.2015.12.016 (DOI)000370467900017 ()
Funder
Swedish Research Council
Available from: 2015-11-24 Created: 2015-11-24 Last updated: 2017-12-01Bibliographically approved
2. Magnetic structure of the magnetocaloric compound AlFe2B2
Open this publication in new window or tab >>Magnetic structure of the magnetocaloric compound AlFe2B2
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2016 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 654, 784-791 p.Article in journal (Refereed) Published
Abstract [en]

The crystal and magnetic structures of AlFe2B2 have been studied with a combination of X-ray and neutron diffraction and electronic structure calculations. The magnetic and magnetocaloric properties have been investigated by magnetisation measurements. The samples have been produced using high temperature synthesis and subsequent heat treatments. The compound crystallises in the orthorhombic crystal system Cmmm and it orders ferromagnetically at 285 K through a second order phase transition. At temperatures below the magnetic transition the magnetic moments align along the crystallographic a-axis. The magnetic entropy change from 0 to 800 kA/m was found to be - 1.3 J/K kg at the magnetic transition temperature.

National Category
Inorganic Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-267573 (URN)10.1016/j.jallcom.2015.12.111 (DOI)000369061700101 ()
Funder
Swedish Research Council
Available from: 2015-11-24 Created: 2015-11-24 Last updated: 2017-12-01Bibliographically approved
3. Irreversible structure change of the as prepared FeMnP1−xSix-structure on the initial cooling through the curie temperature
Open this publication in new window or tab >>Irreversible structure change of the as prepared FeMnP1−xSix-structure on the initial cooling through the curie temperature
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2015 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 374, 455-458 p.Article in journal (Refereed) Published
Abstract [en]

FeMnP0.75Si0.25 experiences a first order para- to ferromagnetic transition at about 200 K. In common with some other alloy compositions crystallizing in the Fe2P structure, the magnetic transition of the as prepared alloy occurs at a lower temperature than on subsequent cooling events. This virgin effect is found to be accompanied by a magnetostrictively induced irreversible structure change that persists on succeeding cooling heating cycles. These findings provide means to understand and control the thermal hysteresis of the (Fe1-xMnx)(2)P1-ySiy alloy system which is a promising material class for use in magnetocaloric refrigerators.

Keyword
FeMnP0.75Si0.25, First order ferromagnetic transition, Thermal hysteresis, Virgin effect, X-ray powder diffraction, Magnetocalorics
National Category
Inorganic Chemistry Engineering and Technology
Research subject
Chemistry with specialization in Inorganic Chemistry; Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-233462 (URN)10.1016/j.jmmm.2014.08.088 (DOI)000344949000073 ()
Funder
Swedish Research Council
Available from: 2014-10-07 Created: 2014-10-06 Last updated: 2017-12-05Bibliographically approved

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Cedervall, Johan

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