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Author: Prodan Lilian Degree: doctor of Physics Speciality:  01.04.10 - Semiconductors physics and engineering Year: 2019 Scientific adviser: Vladimir Ţurcan doctor habilitat, associate professor (docent), Institute of Applied Physics of the Institution: Institute of Applied Physics of the

Status The thesis was presented on the 11 March, 2019 Approved by NCAA on the 19 April, 2019 Abstract – 1.36 Mb / in romanian Thesis CZU 539.21:537.621(043.2) 7.29 Mb / in romanian 171 pages

Keywords

Summary

The dissertation has been completed at Chisinau, is written in Romanian language and contains the following parts: introduction, three chapters, general conclusions and recommendations, 183 references, 118 pages of the main text, 96 figures, 3 tables, and 7 annexes.

The dissertation corresponds to the research field of “Materials sciences and technology” and is dedicated to elaboration of the technology of preparation of poly- and single crystals of the magnetic compounds of AB2X4 and study of their physical properties. Using the chemical transport reactions method the perfect single crystals of the transition and rare-earth metals chalcogenides with composition AB2X4 (A = Mn, Hg, Co, Fe, Cu, Cd; B = Cr, Sc, Er, Yb; X = S, Se), have been successfully grown. The single crystalline samples of CdLn2Se4 (Ln = Er, Yb) lanthanides were grown for the first time. The structural analysis by X-rays powder diffraction confirmed the normal spinel structure and the absence of impurities. X-ray single crystalline analysis of FeSc2S4 samples confirmed pure spinel structure of the stoichiometric samples and the evidenced the secondary phase in the non-stoichiometric Fe1+xSc2-xS4 samples with iron excess. The excess Fe forms a second phase with a regular diffraction pattern corresponding to a vacancy ordered iron sulfide with composition close to the 5C polytype of pyrrhotite Fe9S10. Study of the magnetic properties in a large range of temperature (2 ² T ² 700 K), in static (up to 17 T) and pulse ( up to 120 T) magnetic fields allowed to obtain new information about the magnetic ground state of studied materials. The values of main magnetic parameters have been calculated and compared with the literature values. For the first time, the H-T phase diagrams of the frustrated magnetic compounds of ACr2S4 (A = Mn, Hg, Co), based on the magnetic and elastic data, were evidenced.

The obtained results were published in 24 scientific publication, 7 – articles in the international scientific journals, 17 – as abstracts at national and international scientific conferences.

Oficial Reviewers

• Anatol Sidorenco
  doctor habilitat, professor, Institute of the Electronic Engineering and Nanotechnologies
• Dumitru Ţiuleanu
  doctor habilitat, professor, Technical University of Moldova

Council's Members

• Leonid Culiuc, president
  doctor habilitat, professor, Institute of Applied Physics of the
• Alexandr Nateprov, secretary
  doctor, associate professor (docent)
• Sofia Clochişner, member
  doctor habilitat, professor
• Teodor Munteanu, member
  doctor habilitat, professor
• Dmitrii Nedeoglo, member
  doctor habilitat, professor, Moldova State University
• Emil Rusu, member
  doctor habilitat, associate professor (docent), Practical Scientific Institute of Horticulture and Food Technology
• Veaceslav Ursachi, member
  doctor habilitat, associate professor (docent), Institute of Applied Physics of the

 Theses