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Structure-Magnetic Relationships in the Fe-Mn-P-Si System for Energy Applications
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.ORCID iD: 0000-0001-7855-3308
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Demands for new, energy-efficient appliances have greatly increased in response to our growing need for a more environmentally friendly society. Magnetic refrigeration is a technique that utilizes the magnetocaloric effect, with possible energy savings of up to 30% compared to commercial gas compression refrigerators. A material appropriate for commercial magnetocaloric devices should be both cheap and non-toxic; it should also exhibit a first-order magnetic transitions close to room temperature. The magnetic properties of Fe2P-related materials can be relevant in this context, since their magnetic properties can be finely tuned through the substitution of Fe by Mn and P by Si, As, Ge or B to meet the general requirements for a magnetocaloric device.

An in-depth study has therefore here been made of the structural and magnetic properties of the (Fe,Mn)2(P,Si)-system. The phase diagram of the FeMnP1-xSix-system has been carefully re-examined. It is found to contain two single-phase regions: an orthorhombic Co2P-type structure (x < 0.15) and a hexagonal Fe2P-type structure (0.24 ≤ x < 0.50). Selected compounds within the Fe2P-type region of the phase diagram have been shown to exhibit potential for use in magnetic refrigeration applications.

Neutron powder diffraction has here been used to determine the magnetic structures of selected crystalline compositions within the FeMnP1-xSix-system to gain a better understanding of its magnetic properties. The Fe2P-type region is mainly ferromagnetic, but an incommensurate antiferromagnetic structure has also been identified close to the Co2P/Fe2P-type phase border for x ≈ 0.25.

The so-called ''virgin effect'' in the Fe2P-type region of the FeMn(P,Si) phase diagram is found to be accompanied by an irreversible structural phase transition induced by magnetostriction. This new phase is found to be preserved during successive cooling-heating cycles. Furthermore, the magnetic properties of the substituted Fe2P-type structure changes significantly for metal:non-metal ratios away from 2:1. Such deviations could well explain the apparently conflicting structure-property relationships described in earlier literature for the FeMnP1-xSix-system.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. , 74 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1197
Keyword [en]
Magnetocaloric, X-ray powder diffraction, Neutron powder diffraction, Magnetization measurements, Phase diagram, Crystal structure, Magnetic structure, Incommensurate structure, Ferromagnetic, Antiferromagnetic, Fe2P, Fe-Mn-P-Si.
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-234516ISBN: 978-91-554-9091-1 (print)OAI: oai:DiVA.org:uu-234516DiVA: diva2:757701
Public defence
2014-12-12, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2014-11-20 Created: 2014-10-20 Last updated: 2015-02-03
List of papers
1. The crystal and magnetic structure of the magnetocaloric compound FeMnP0.5Si0.5
Open this publication in new window or tab >>The crystal and magnetic structure of the magnetocaloric compound FeMnP0.5Si0.5
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2011 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 184, no 9, 2434-2438 p.Article in journal (Refereed) Published
Abstract [en]

The crystal and magnetic structure of the magnetocaloric compound FeMnP0.5Si0.5 has been studied by means of neutron and X-ray powder diffraction. Single phase samples of nominal composition FeMnP0.5Si0.5 have been prepared by the drop synthesis method. The compound crystallizes in the Fe2P-type structure (P-62m) with the magnetic moments aligned along the a-axis. It is found that the Fe atoms are mainly situated in the tetrahedral 3g site while the Mn atoms prefer the pyramidal 3f position. The material is ferromagnetic (TC=382 K) and at 296 K the total magnetic moment is 4.4 µB/f.u. It is shown that the magnetic moment in the 3f site is larger (2.5 µB) than in the 3g site (1.9 µB).

Keyword
Magnetocaloric, Neutron powder diffraction, X-ray diffraction (XRD), Drop synthesis method, Magnetic refrigeration, Magnetic structure
National Category
Natural Sciences Engineering and Technology Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry; Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-159482 (URN)10.1016/j.jssc.2011.06.019 (DOI)000294835700019 ()
Available from: 2011-10-03 Created: 2011-10-03 Last updated: 2017-12-08
2. Strongly enhanced magnetic moments in ferromagnetic FeMnP0.5Si0.5
Open this publication in new window or tab >>Strongly enhanced magnetic moments in ferromagnetic FeMnP0.5Si0.5
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2011 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 99, no 15, 152502- p.Article in journal (Refereed) Published
Abstract [en]

The compound FeMnP(0.5)Si(0.5) has been studied by magnetic measurements, Mossbauer spectroscopy, and electronic structure and total energy calculations. An unexpectedly high magnetic hyperfine field for Fe atoms located at the tetrahedral Me(1) site in the Fe(2)P structure is found, The saturation moment derived from magnetic measurements corresponds to 4.4 mu(B)/f.u. at low temperatures, a value substantially higher than previously reported, but in accordance with the results from our electron structure calculations, This high saturation moment and the tunable first order ferromagnetic transition make the Fe(2-x)Mn(x)P(1-y)Si(y), system promising for magnetocaloric applications.

Keyword
electronic structure, iron alloys, magnetic moments, magnetic transitions, magnetocaloric effects, manganese alloys, Mossbauer effect, phosphorus alloys, silicon alloys, total energy
National Category
Physical Sciences Inorganic Chemistry Engineering and Technology
Research subject
Inorganic Chemistry; Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-161941 (URN)10.1063/1.3651272 (DOI)000295883800051 ()
Available from: 2011-11-23 Created: 2011-11-21 Last updated: 2017-12-08
3. Detailed study of the magnetic ordering in FeMnP0.75Si0.25
Open this publication in new window or tab >>Detailed study of the magnetic ordering in FeMnP0.75Si0.25
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2015 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 221, 240-246 p.Article in journal (Refereed) Published
Abstract [en]

Magnetic and crystallographic properties of FeMnP0.75Si0.25 in the hexagonal Fe2P-type structure have been investigated by X-ray powder diffraction, neutron powder diffraction and magnetic measurements. The room temperature diffractograms reveal co-existence of two distinct structural phases in the samples with small, but significant, differences only in the unit cell dimensions. The volume ratio between the two phases is governed by the annealing conditions. One of the phases orders ferromagnetically (TC = 250 K) and the other in an incommensurate antiferromagnetic structure at low temperatures (qx = 0.363(1), TN = 150 K).

Keyword
Magnetic structure, Incommensurate ordering, Neutron powder diffraction, X-ray powder diffraction (XRD), Magnetization
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-234509 (URN)10.1016/j.jssc.2014.10.013 (DOI)000347263700034 ()
Available from: 2014-10-20 Created: 2014-10-20 Last updated: 2017-12-05Bibliographically approved
4. 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
5. Phase diagram, structures and magnetism of the FeMnP1-xSix-system
Open this publication in new window or tab >>Phase diagram, structures and magnetism of the FeMnP1-xSix-system
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2015 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 5, no 11, 8278-8284 p.Article in journal (Refereed) Published
Abstract [en]

The magnetic properties of the (Fe,Mn)2(P,Si)-system have been shown to be readily manipulated by small changes in composition. This study surveys the FeMnP1−xSix-system (0.00 ≤ x ≤ 1.00) reporting sample syntheses and investigations of crystallographic and magnetic properties using X-ray powder diffraction and magnetic measurements. Two single phase regions exist: the orthorhombic Co2P-type structure (x < 0.15) and the Fe2P-type structure (0.24 ≤ x < 0.50). Certain compositions have potential for use in magnetocaloric applications.

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-234515 (URN)10.1039/C4RA15419C (DOI)000347720900065 ()
Available from: 2014-10-22 Created: 2014-10-20 Last updated: 2017-12-05Bibliographically approved

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