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Synthesis and characterization of Ga-containing MAX phase thin films
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The study of magnetic Mn+1AXn (MAX) phases (n = 1 − 3, M – a transition metal, A – an A group element, X – C or N) is a recently established research area, fuelled by theoretical predictions and first confirmed experimentally through alloying of Mn into the well-known Cr2AlC and Cr2GeC. Theoretical phase stability investigations suggested a new magnetic MAX phase, Mn2GaC, containing Ga which is liquid close to room temperature. Hence, alternative routes for MAX phase synthesis were needed, motivating a further development of magnetron sputtering from liquid targets.

In this thesis, (Cr1-xMnx)2GaC 0 ≤ x ≤ 1  MAX phase thin films have been synthesized from elemental and/or compound targets, using ultra high vacuum magnetron sputtering. Initial thin film synthesis of Cr2GaC was performed using elemental targets, including liquid Ga. Process optimization ensured optimal target size and crucible geometry for containing the Ga. Films were deposited at 650 °C on MgO(111) substrates. X-ray diffraction and transmission electron microscopy confirms the growth of epitaxial Cr2GaC MAX phase with minor inclusions of Cr3Ga.

To explore the magnetic characteristics upon Mn alloying, synthesis of (Cr0.5Mn0.5)2GaC thin films was performed from elemental Ga and C and a composite Cr/Mn target of 1:1 composition. Films were deposited on MgO(111), Al2O3(0001) (with or without NbN seed layer), and 4° off-cut 4H-SiC(0001) substrates. The films are smooth and of high structural quality as confirmed by X-ray diffraction and transmission electron microscopy. The film composition measured by high resolution energy dispersive X-ray spectroscopy confirms a composition corresponding to (Cr0.5Mn0.5)2GaC. The magnetic response, as measured with vibrating sample magnetometry, displays a ferromagnetic component, however, the temperature dependence of the magnetic moments and saturation fields suggests competing magnetic interaction and possible non-collinear magnetic ordering.

Finally, inspired by theoretical predictions, a new member of the MAX phase family, Mn2GaC, was synthesized. This is the first MAX phase containing Mn as a sole M element. X-ray diffraction and transmission electron microscopy confirms the characteristic MAX phase structure with a 2:1:1 composition. Theoretical work suggests that the magnetic ground state is almost degenerate between ferromagnetic and anti-ferromagnetic. Vibrating sample magnetometry shows ferromagnetic response with a transition temperature Tc of 230 K. However, also for this phase, complex magnetism is suggested. Altogether, the results indicate a new family of magnetic nanolaminates with a rich variation of magnetic ground states.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 29 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1680
National Category
Physical Sciences Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-110764DOI: 10.3384/lic.diva-110764ISBN: 978-91-7519-224-6 (print)OAI: oai:DiVA.org:liu-110764DiVA: diva2:748742
Presentation
2014-10-23, Planck, Fysikhuset, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2014-09-22 Created: 2014-09-22 Last updated: 2017-10-17Bibliographically approved
List of papers
1. Phase stability of Crn+1GaCn MAX phases from first principles and Cr2GaC thin-film synthesis using magnetron sputtering from elemental targets
Open this publication in new window or tab >>Phase stability of Crn+1GaCn MAX phases from first principles and Cr2GaC thin-film synthesis using magnetron sputtering from elemental targets
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2013 (English)In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 7, no 11, 971-974 p.Article in journal (Refereed) Published
Abstract [en]

Ab-initio calculations have been used to investigate the phase stability and magnetic state of Crn+ 1GaCn MAX phase. Cr2GaC (n = 1) was predicted to be stable, with a ground state corresponding to an antiferromagnetic spin configuration. Thin-film synthesis by magnetron sputtering from elemental targets, including liquid Ga, shows the formation of Cr2GaC, previously only attained from bulk synthesis methods. The films were deposited at 650 degrees C on MgO(111) substrates. X-ray diffraction and high-resolution transmission electron microscopy show epitaxial growth of (000) MAX phase.

Place, publisher, year, edition, pages
Wiley-VCH Verlag, 2013
Keyword
MAX phases; ab-initio calculations; magnetron sputtering; epitaxial thin films
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-103307 (URN)10.1002/pssr.201308025 (DOI)000328321700009 ()
Available from: 2014-01-16 Created: 2014-01-16 Last updated: 2017-12-06
2. Synthesis and characterization of magnetic (Cr0.5Mn0.5)2GaC thin films
Open this publication in new window or tab >>Synthesis and characterization of magnetic (Cr0.5Mn0.5)2GaC thin films
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2015 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 50, no 13, 4495-4502 p.Article in journal (Refereed) Published
Abstract [en]

Growth of (Cr0.5Mn0.5)2GaC thin films from C, Ga, and compound Cr0.5Mn0.5 targets is reported for depositions on MgO (111), 4H-SiC (0001), and Al2O3 (0001) with and without a NbN (111) seed layer. Structural quality is found to be highly dependent on the choice of substrate with MgO (111) giving the best results as confirmed by X-ray diffraction and transmission electron microscopy. Phase pure, high crystal quality MAX phase thin films are realized, with a Cr:Mn ratio of 1:1. Vibrating sample magnetometry shows a ferromagnetic component from 30 K up to 300 K, with a measured net magnetic moment of 0.67 μB per metal (Cr + Mn) atom at 30 K and 5 T. The temperature dependence of the magnetic response suggests competing magnetic interactions with a resulting non-collinear magnetic ordering.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2015
Keyword
magnetism, thin films, magnetron sputtering, MAX phase
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-118837 (URN)10.1007/s10853-015-8999-8 (DOI)000354093500005 ()
Note

At the time for thesis presentation publication was in status: Manuscript

Funding Agencies|European Research Council under the European Community [258509]; Swedish Research Council (VR) [642-2013-8020, 621-2012-4425]; KAW Fellowship program; SSF synergy grant FUNCASE; Icelandic University Research fund

Available from: 2015-06-08 Created: 2015-06-04 Last updated: 2017-12-04Bibliographically approved
3. A Nanolaminated Magnetic Phase: Mn2GaC
Open this publication in new window or tab >>A Nanolaminated Magnetic Phase: Mn2GaC
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2014 (English)In: Materials Research Letters, ISSN 2166-3831, Vol. 2, no 2, 89-93 p.Article in journal (Refereed) Published
Abstract [en]

Layered magnetic materials are fascinating from the point of view of fundamental science as well as applications. Discoveries such as giant magnetoresistance (GMR) in magnetic multilayers have revolutionized data storage and magnetic recording, and concurrently initiated the search for new layered magnetic materials. One group of inherently nanolaminated compounds are the so called Mn+1AXn (MAX) phases. Due to the large number of isostructural compositions, researchers are exploring the wide range of interesting properties, and not primarily functionalization through optimization of structural quality. Magnetic MAX phases have been discussed in the literature, though this is hitherto an unreported phenomenon. However, such materials would be highly interesting, based on the attractive and useful properties attained with layered magnetic materials to date. Here we present a new MAX phase, (Cr1–xMnx)2GeC, synthesized as thin film in heteroepitaxial form, showing single crystal material with unprecedented structural MAX phase quality. The material was identified using first-principles calculations to study stability of hypothetical MAX phases, in an eort to identify a potentially magnetic material. The theory predicts a variety of magnetic behavior depending on the Mn concentration and Cr/Mn atomic conguration within the sublattice. The analyzed thin films display a magnetic signal well above room temperature and with partly ferromagnetic ordering. These very promising results open up a field of new layered magnetic materials, with high potential for electronics and spintronics applications.

Place, publisher, year, edition, pages
Taylor & Francis, 2014
Keyword
MAX phases, sputtering, transmission electron microscopy (TEM), ab initio calculation
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-77774 (URN)10.1080/21663831.2013.865105 (DOI)
Note

On the day of the defence date the status of this article was previous Manuscript. The original title of the Manuscript was Magnetic nanoscale laminates from first principles and thin film synthesis.

Available from: 2012-05-29 Created: 2012-05-29 Last updated: 2017-11-03Bibliographically approved

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