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Synthesis and characterization of magnetic nanolaminated carbides
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

MAX phases are a group of nanolaminated ternary carbides and nitrides, with a composition expressed by the general formula Mn+1AXn (ūĚĎõ = 1 ‚ąí 3), where M is a transition metal, A is an A-group element, and X is carbon and/or nitrogen. MAX phases have attracted interest due to their unique combination of metallic and ceramic properties, related to their inherently laminated structure of a transition metal carbide (Mn+1Xn) layer interleaved by an A-group metal layer.

This Thesis explores synthesis and characterization of magnetic MAX phases, where the A-group element is gallium (Ga). Due to the low melting point of Ga (T = 30 ¬įC), conventional thin film synthesis methods become challenging, as the material is in liquid form at typical process temperatures. Development of existing methods has therefore been investigated, for reliable/reproducible synthesis routes, including sputtering from a liquid target, and resulting high quality material. Routes for minimizing trial-and-error procedures during optimization of thin film synthesis have also been studied, allowing faster identification of optimal deposition conditions and a simplified transfer of essential deposition parameters between different deposition systems.

A large part of this Thesis is devoted towards synthesis of MAX phase thin films in the Cr-Mn-Ga-C system. First, through process development, thin films of Cr2GaC were deposited by magnetron sputtering. The films were epitaxial, however with small amount of impurity phase Cr3Ga, as confirmed by X-ray diffraction (XRD) measurements. The film structure was confirmed by scanning transmission electron microscopy (STEM) and the composition by energy dispersive X-ray spectroscopy (EDX) inside the TEM.

Inspired by predictive ab initio calculations, the new MAX phase Mn2GaC was successfully synthesized in thin film form by magnetron sputtering. Structural parameters and magnetic properties were analysed. The material was found to have two magnetic transitions in the temperature range 3 K to 750 K, with a first order transition at around 214 K, going from non-collinear antiferromagnetic state at lower temperature to an antiferromagnetic state at higher temperature. The Neél temperature was determined to be 507 K, changing from an antiferromagnetic to a paramagnetic state. Above 800 K, Mn2GaC decomposes. Furthermore, magnetostrictive, magnetoresistive and magnetocaloric properties of the material were iv determined, among which a drastic change in lattice parameters upon the first magnetic transition was observed. This may be of interest for magnetocaloric applications.

Synthesis of both Cr2GaC and Mn2GaC in thin film form opens the possibility to tune the magnetic properties through a solid solution on the transition metal site, by alloying the aforementioned Cr2GaC with Mn, realizing (Cr1-xMnx)2GaC. From a compound target with a Cr:Mn ratio of 1:1, thin films of (Cr0.5Mn0.5)2GaC were synthesized, confirmed by TEM-EDX. Optimized structure was obtained by deposition on MgO substrates at a deposition temperature of 600 ¬ļC. The thin films were phase pure and of high structural quality, allowing magnetic measurements. Using vibrating sample magnetometry (VSM), it was found that (Cr0.5Mn0.5)2GaC has a ferromagnetic component in the temperature range from 30 K to 300 K, with the measured magnetic moment at high field decreasing by increasing temperature. The remanent moment and coercive field is small, 0.036 őľB, and 12 mT at 30 K, respectively. Using ferromagnetic resonance spectroscopy, it was also found that the material has pure spin magnetism, as indicated by the determined spectroscopic splitting factor g = 2.00 and a negligible magnetocrystalline anisotropy energy.

Fuelled by the recent discoveries of in-plane chemically ordered quaternary MAX phases, so called i-MAX phases, and guided by ab initio calculations, new members within this family, based on Cr and Mn, were synthesized by pressureless sintering methods, realizing (Cr2/3Sc1/3)2GaC and (Mn2/3Sc1/3)2GaC. Their structural properties were determined. Through these phases, the Mn content is the highest obtained in a bulk MAX phase to date.

This work has further developed synthesis processes for sputtering from liquid material, for an optimized route to achieve thin films of controlled composition and a high structural quality. Furthermore, through this work, Mn has been added as a new element in the family of MAX phase elements. It has also been shown, that alloying with different content of Mn gives rise to varying magnetic properties in MAX phases. As a result of this Thesis, it is expected that the MAX phase family can be further expanded, with more members of new compositions and new properties.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. , p. 58
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1918
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-145679DOI: 10.3384/diss.diva-145679ISBN: 9789176853429 (print)OAI: oai:DiVA.org:liu-145679DiVA, id: diva2:1190688
Public defence
2018-04-16, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2018-03-15 Created: 2018-03-15 Last updated: 2019-09-30Bibliographically 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, p. 971-974Article 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
Keywords
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: 2018-03-15
2. 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, p. 89-93Article 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‚ÄďxMnx)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
Keywords
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: 2018-03-15Bibliographically approved
3. Large uniaxial magnetostriction with sign inversion at the first order phase transition in the nanolaminated Mn2GaC MAX phase
Open this publication in new window or tab >>Large uniaxial magnetostriction with sign inversion at the first order phase transition in the nanolaminated Mn2GaC MAX phase
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2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, no 1, article id 2637Article in journal (Refereed) Published
Abstract [en]

In 2013, a new class of inherently nanolaminated magnetic materials, the so called magnetic MAX phases, was discovered. Following predictive material stability calculations, the hexagonal Mn2GaC compound was synthesized as hetero-epitaxial films containing Mn as the exclusive M-element. Recent theoretical and experimental studies suggested a high magnetic ordering temperature and non-collinear antiferromagnetic (AFM) spin states as a result of competitive ferromagnetic and antiferromagnetic exchange interactions. In order to assess the potential for practical applications of Mn2GaC, we have studied the temperature-dependent magnetization, and the magnetoresistive, magnetostrictive as well as magnetocaloric properties of the compound. The material exhibits two magnetic phase transitions. The N√©el temperature is T N ‚ÄČ~‚ÄČ507‚ÄČK, at which the system changes from a collinear AFM state to the paramagnetic state. At T t ‚ÄČ=‚ÄČ214‚ÄČK the material undergoes a first order magnetic phase transition from AFM at higher temperature to a non-collinear AFM spin structure. Both states show large uniaxial c-axis magnetostriction of 450 ppm. Remarkably, the magnetostriction changes sign, being compressive (negative) above T t and tensile (positive) below the T t . The sign change of the magnetostriction is accompanied by a sign change in the magnetoresistance indicating a coupling among the spin, lattice and electrical transport properties.

Place, publisher, year, edition, pages
London: Nature Publishing Group, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-145680 (URN)10.1038/s41598-018-20903-2 (DOI)
Available from: 2018-03-15 Created: 2018-03-15 Last updated: 2018-03-15Bibliographically approved
4. 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, p. 4495-4502Article 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¬†őľB 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
Keywords
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: 2018-03-15Bibliographically approved
5. Magnetic Anisotropy in the (Cr0.5Mn0.5)(2)GaC MAX Phase
Open this publication in new window or tab >>Magnetic Anisotropy in the (Cr0.5Mn0.5)(2)GaC MAX Phase
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2015 (English)In: MATERIALS RESEARCH LETTERS, ISSN 2166-3831, Vol. 3, no 3, p. 156-160Article in journal (Refereed) Published
Abstract [en]

Magnetic MAX phase (Cr0.5Mn0.5)(2)GaC thin films grown epitaxially on MgO(111) substrates were studied by ferromagnetic resonance at temperatures between 110 and 300 K. The spectroscopic splitting factor g = 2.00 +/- 0.01 measured at all temperatures indicates pure spin magnetism in the sample. At all temperatures we find the magnetocrystalline anisotropy energy to be negligible which is in agreement with the identified pure spin magnetism.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS INC, 2015
Keywords
Magnetic MAX Phase; Ferromagnetic Resonance; g-Factor; Magnetic Anisotropy
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-127070 (URN)10.1080/21663831.2015.1036324 (DOI)000372219300006 ()
Note

Funding Agencies|EC [280670]; UDE; ERC [258509]; Swedish Research Council (VR) [642-2013-8020]; SSF synergy grant FUNCASE

Available from: 2016-04-13 Created: 2016-04-13 Last updated: 2018-03-15
6. Toward Structural Optimization of MAX Phases as Epitaxial Thin Films
Open this publication in new window or tab >>Toward Structural Optimization of MAX Phases as Epitaxial Thin Films
2016 (English)In: MATERIALS RESEARCH LETTERS, ISSN 2166-3831, Vol. 4, no 3, p. 152-160Article in journal (Refereed) Published
Abstract [en]

Prompted by the increased focus on MAX phase materials and their two-dimensional counterparts MXenes, a brief review of the current state of affairs in the synthesis of MAX phases as epitaxial thin films is given. Current methods for synthesis are discussed and suggestions are given on how to increase the material quality even further as well as arrive at those conditions faster. Samples were prepared to exemplify the most common issues involved with the synthesis, and through suggested paths for resolving these issues we attain samples of a quality beyond what has previously been reported.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS INC, 2016
Keywords
MAX Phase; Thin Films; Reproducible Materials Synthesis; Sample Quality
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-132496 (URN)10.1080/21663831.2016.1157525 (DOI)000385011000004 ()
Note

Funding Agencies|European Research Council under the European Community Seventh Framework Program (FP7)/ERC Grant [258509]; Swedish Research Council (VR); Knut and Alice Wallenberg (KAW) Fellowship program; SSF synergy grant FUNCASE

Available from: 2016-11-13 Created: 2016-11-12 Last updated: 2018-03-15

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