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Institute of Applied Physics
5 Academiei str.
Chisinau, MD-2028
MOLDOVA (Rep. of)
phone: +(373) 22 738150
fax: +(373) 22 738149
email: [javascript protected email address]

Project ANCD 20.80009.5007.19 New uni-, bi- and three-dimensional materials with controlled magnetic, optical and dielectric properties based on transition metals

Type : Project within the State Programs funded by the National Agency for Research and Development of the Republic of Moldova
Head : Leonid Kulyuk, Dr.Sc., prof., acad. ASM
Duration : 2020 - 2023
Division(s) : Laboratory of Physics of Semiconductor Compounds “Sergiu Radautsan”

The project was focused on preparation, characterization and modeling of new materials with adjustable magnetic, optical and semiconductor/dielectric properties for application in spintronics, opto- and nanoelectronics. The objects of study were bi- and tridimensional compounds containing transition metals: (i) polar magnetic materials with lacunar spinel structure AB4X8 (A=Ga, Al, Ge; B=V, Nb, Ta; X=S, Se) with spin-vortex nano-objects like skyrmions; (ii) magnetic compounds Me2Mo3O8 (Me=Mn, Fe, Co) with hexagonal structure; (iii) bulk layered crystals, two-dimensional (2D) exfoliated nanosheets and CVD deposited ultrathin films of transition metal dichalcogenides TX2 (T=Mo, W; X=S, Se), as grown, doped with other transition metals and intercalated by halogen molecules, as well as the van der Waals semiconductor heterostructures formed by 2D layers with different compositions; (iv) molecular systems manifesting spin transitions under external stimuli. The properties of the grown perfect bulk (3D) single crystals of magnetic and TX2 compounds and 2D nanosheets and van der Waals layered heterostructures were studied in order to elucidate the mechanisms of formation of skyrmion states, of exchange interactions, of the ground state and of the excited electronic states, of orbital and ferroelectric ordering, of the origin of the Mott memory, of the free and bound excitons, charge carriers recombination processes and of optical phenomena emerging at the interface of the layered systems. Advanced methods, such as SQUID magnetometry, ultrasound spectroscopy in high magnetic fields (up to 70T), neutron scattering, atomic force microscopy, optical spectroscopy (including IR and THz domains), Raman, magneto-optical and luminescence spectroscopies, as well as nonlinear-optical characterization techniques were applied. General theoretical models supported by DFT calculations were developed and employed for the explanation of magnetic and spectroscopic properties of new systems obtained during the project implementation as well as of switchable materials on the base of mono- , tri- and tetranuclear transition metal clusters manifesting charge transfer induced spin transitions or spin crossover. These models were properly take into account electron transfer, superexchange, vibronic coupling and cooperative interactions. The mechanisms of formation of switchable properties were elucidated. The project was combined efforts of experimenters and theorists led by wellrecognized researchers in solid state physics and materials science (including nano-materials), theory of magnetic interactions, vibronic effects, cooperative phenomena and quantum-mechanical calculations.

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