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Correlation between magnetic state and bulk modulus of Cr2AlC
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 21Article in journal (Refereed) Published
Abstract [en]

The effect of magnetism on the bulk modulus (B0) of M2AlC (M  = Ti, V, and Cr) has been studied using first principles calculations. We find that it is possible to identify an energetically favorable magnetic Cr2AlC phase without using any adjustable parameter, such as the Hubbard U. Furthermore, we show that an in-plane spin polarized configuration has substantially lower B0 as compared to the non-magnetic model. The existences of local magnetic moments on Cr atoms considerably improve agreement between theory and experiment regarding trends in B0 for M2AlC phases.

Place, publisher, year, edition, pages
American Institute of Physics (AIP) , 2013. Vol. 113, no 21
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-96430DOI: 10.1063/1.4808239ISI: 000320674500104OAI: diva2:641924

Funding Agencies|European Research Council under the European Community|258509|Swedish Research Council (VR)|621-2012-4425621-2011-4417|

Available from: 2013-08-20 Created: 2013-08-19 Last updated: 2014-02-25
In thesis
1. Materials Design from First Principles: stability and magnetism of nanolaminates
Open this publication in new window or tab >>Materials Design from First Principles: stability and magnetism of nanolaminates
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, first-principles calculations within density functional theory are presented, with a principal goal to investigate the phase stability of so called Mn+1AXn (MAX) phases. MAX phases are a group of nanolaminated materials comprised of a transition metal (M), a group 12-16 element (A), and carbon or nitrogen (X). They combine ceramic and metallic characteristics, and phase stability studies are motivated by a search for new phases with novel properties, such as magnetism, and for the results to be used as guidance in attempted materials synthesis in the lab.

To investigate phase stability of a hypothetical material, a theoretical approach has been developed, where the essential part is to identify the set of most competing phases relative to the material of interest. This approach advance beyond more traditional evaluation of stability, where the energy of formation of the material is generally calculated relative to its single elements, or to a set of ad hoc chosen competing phases. For phase stability predictions to be reliable, validation of previous experimental work is a requirement prior to investigations of new, still hypothetical, materials. It is found that the predictions from the developed theoretical approach are consistent with experimental observations for a large set of MAX phases. The predictive power is thereafter demonstrated for the new phases Nb2GeC and Mn2GaC, which subsequently have been synthesized as thin films. It should be noted that Mn is used for the first time as sole M-element in a MAX phase. Hence, the theory is successfully used to find new candidates, and to guide experimentalists in their work on novel promising materials. Phase stability is also evaluated for MAX phase alloys. Incorporation of oxygen in different M2AlC phases are studied, and the results show that oxygen prefer different sites depending on M-element, through the number of available non-bonding M d-electrons. The theory also predicts that oxygen substituting for carbon in Ti2AlC stabilizes the material, which explains the  experimentally observed 12.5 at% oxygen (x = 0.5) in Ti2Al(C1-xOx).

Magnetism is a recently attained property of MAX phase materials, and a direct result of this Thesis work. We have demonstrated the importance of choice of magnetic spin configuration and electron correlations approximations for theoretical evaluation of the magnetic ground state of Cr2AC (A = Al, Ga, Ge). Furthermore, alloying Cr2AlC with Mn to obtain the first magnetic MAX phase have been theoretically predicted and experimentally verified. Using Mn2GaC as model system, Heisenberg Monte Carlo simulations have been used to explore also noncollinear magnetism, suggesting a large set of possible spin configurations (spin waves and spin spirals) to be further investigated in future theoretical and experimental work.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 81 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1571
National Category
Natural Sciences
urn:nbn:se:liu:diva-104764 (URN)10.3384/diss.diva-104764 (DOI)978-91-7519-411-0 (print) (ISBN)
Public defence
2014-03-14, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 09:15 (English)
Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2014-02-25Bibliographically approved

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