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Rare-earth (RE) nanolaminates Mo4RE4Al7C3 featuring ferromagnetism and mixed-valence states
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Univ Grenoble Alpes, France.
Univ Grenoble Alpes, France.
Univ Grenoble Alpes, France.
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2018 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 2, no 11, article id 114401Article in journal (Refereed) Published
Abstract [en]

Rare-earth-based (RE) nanolaminates have attracted attention recently because of their complicated magnetism and their potential as precursors for strongly correlated two-dimensional materials. In this work, we synthesized a class of nanolaminates with a Mo4RE4Al7C3 chemistry, where RE = Ce or Pr. Powder samples of both phases were characterized with respect to structure and composition. Single crystals of Mo4Ce4Al7C3 were used for magnetization measurements. The crystal structure was investigated by means of x-ray diffraction and scanning transmission electron microscopy. Magnetization analysis reveals a ferromagnetic ground state with a Curie temperature of similar to 10.5 K. X-ray absorption near-edge structure provides experimental evidence that Ce is in a mixed-valence state. X-ray magnetic circular dichroism shows that only the Ce atoms with 4f(1) configuration occupying one of the two possible sites are ferromagnetically coupled, with a saturation moment of similar to 1.2 mu(B) per atom. We thus classify Mo4Ce4Al7C3 as a ferromagnetic, mixed-valence compound.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC , 2018. Vol. 2, no 11, article id 114401
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-153172DOI: 10.1103/PhysRevMaterials.2.114401ISI: 000450570100003OAI: oai:DiVA.org:liu-153172DiVA, id: diva2:1267317
Note

Funding Agencies|Knut and Alice Wallenberg (KAW) Foundation through a Fellowship [0358, KAW 2015.0043]; Swedish Research council [642-2013-8020]; Flag-ERA JTC; chair of excellence program of the Nanosciences Foundation (Universite Grenoble-Alpes Foundation); Federation Wallonie-Bruxelles through the Action de Recherche Concertee "3D nanoarchitecturing of 2D crystals" [16/21-077]; European Union [696656]; Belgium FNRS (Flag-ERA) [R. 50.01.18.F]; Fonds de la Recherche Scientifique de Belgique (F.R.S. -FNRS) [2.5020.11]; Linkoping Ultra Electron Microscopy Laboratory

Available from: 2018-12-01 Created: 2018-12-01 Last updated: 2020-02-21
In thesis
1. Synthesis and characterization of two- and three-dimensional nanolaminated carbides
Open this publication in new window or tab >>Synthesis and characterization of two- and three-dimensional nanolaminated carbides
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focused towards the synthesis and characterization of novel nanolaminated materials in primarily bulk (powder) form. Of particular interest is magnetic materials, or laminates that can be used as precursor for two-dimensional (2D) materials. 2D materials typically display a large surface-to-volume ratio, and as such they are very promising for applications within energy storage and catalysis. A more recently discovered family of 2D transition metal carbides/nitrides, called MXenes, are currently attracting a lot of attention. MXenes are produced by selective etching of parent 3D nanolaminates, so called MAX phases, facilitating removal of selected atomic layers, and formation of 2D sheets.

In my work on new nanolaminates as precursors for 2D materials, I have synthesized (Mo2/3Sc1/3)2AlC and have studied its crystal structure. It was found that Mo and Sc are chemically ordered in the metal layers, with the in-plane ordering motivating the notation i-MAX for this new type of MAX phase alloy. By selective etching of Sc and Al, we thereafter produced a 2D materials with ordered vacancies, Mo1.33C, and studied the electrochemical properties. It was found that the material displayed a high capacitance, ~1200 F cm-3, which is 65% higher that the counterpart without vacancies, Mo2C.

I also synthesized a previously not known out-of-plane ordered Mo2ScAlC2 MAX phase. By selective etching of Al, we produced a 2D material, Mo2ScC2, which is correspondingly ordered in the out-of-plane direction. Another related laminated material was also discovered and synthesized, Sc2Al2C3, and its crystal structure was determined. The material is potentially useful for conversion into a 2D material. I have also shown that Sc2Al2C3 is an example of a series of materials with the same crystal structure, with Sc replaced by other metals.

Magnetic materials are used in many applications, such as for data storage devices. In particular, layered magnetic materials are of interest due to their anisotropic structure and potential formation of interesting magnetic characteristics. I have been synthesizing and characterizing magnetic nanolaminates, starting with the (V,Mn)3GaC2 MAX phase in the form of an epitaxial thin film. Analysis of the magnetic behavior showed a ferromagnetic response above room temperature I thereafter showed that our previously discovered family of i-MAX phases could be expanded with a subclass of ordered nanolaminates based on rare earth (RE) elements, of the general formula (Mo2/3RE1/3)2AlC , where RE=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. I studied their crystal structure by scanning transmission microscopy (STEM), X-ray diffraction (XRD), and neutron diffraction. We found that these phases can crystalize in three different structures, of space group C2/m, C2/c, and Cmcm, respectively. The magnetic behavior was studied and the magnetic structure of two materials could be determined. We suggest that the complex behavior identified is due to competing magnetic interaction and frustration.

I also synthesized another rare earth-based nanolaminate, Mo4Ce4Al7C3. The crystal structure was investigated by single crystal X-ray diffraction and STEM. Magnetization analysis reveal a ferromagnetic ground state below 10.5 K. X-ray absorption near-edge structure provide evidence that Ce is in a mixed-valence state. X-ray magnetic circular dichroism shows that only one of the two Ce sites are magnetic. 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2020. p. 44
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2058
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-163847 (URN)10.3384/diss.diva-163847 (DOI)9789179298791 (ISBN)
Public defence
2020-03-26, F-building, Campus Valla, Linköping, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2020-03-02 Created: 2020-02-21 Last updated: 2020-03-11Bibliographically approved

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