DEPARTMENT OF MAGNETIC AND ELASTIC PROPERTIES OF SOLIDS

Structure and magnetoelastic properties of low-dimensional systems
in the region of low temperature phase transitions

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Staff of Research Group

Valentina A. Sirenko sireeghataruslpostnko@ileghataruslpostt.khareghataruslpostkov.ua Scopus ResearcherID GScholar ORCID	Head of Group, Leading Research Fellow, Prof., DrSc.
Ivan S. Bondar ibondeghataruslpostar@ileghataruslpostt.khareghataruslpostkov.ua Scopus ResearcherID GScholar ORCID	Junior Research Fellow, Dr.rer.nat., PhD.

Main directions of studies

• Structural investigations of magnetics and superconductors at low temperatures.
• Magnetostriction phenomena in magnetics and superconductors in the region of low temperature phase transitions.
• Nanotubes of the transition metals dichalcogenides.
• The structural research of low-dimensional non-organic conductors,as well as electronic charactestistics of low-dimensional graphene-based nanostructures, caused by crystallographic nonhomogeneities of studied materials.
• The study of the features of temperature dependences of lattice parameters and vibrational characteristics of niobium layered diselenide in the region of low-temperature electronic phase transitions.

Main results

• Identification and investigation of quantum magnetization and magnetostriction oscillations in the mixed state of superconductors.
• Revealing of the twining structure appearance under formation of the antiferromagnetic dielectric phase in  Nd_0.5Sr_0.5MnO₃ manganite.
• The detection and explanation of the low-temperature anomaly of the temperature dependence of the coefficients of linear thermal expansion along different directions: in layered crystals formed both by monoatomic layers (graphene nanofilms) and multilayered "sandwiches" (EuBaCuO, 2H-NbSe₂).
• Obtaining of the reproducible closed nanoformations of 2H-NbSe₂ (nanotubes and nanowires).
• Development and construction of the autonomous compact helium combi-cryostat for X-ray studies in temperature region 10-300 K.
• Detection and explanation of the low-temperature anomalies of thermal expansion in EuBaCuO compounds along the c crystal axis, substantially below the Debye temperature.
• The change in the electron and phonon spectra of graphene materials with the formation of the chirality boundary "zigzag" is analyzed analytically and numerically and it is shown that such a defect leads to a significant increase in the number of electrons with energies near the Fermi energy and the number of quasi-bending phonons with frequencies near that one which corresponds to the K-point of the first band Brillouin.

Experimental equipment

• X-rays diffractometer equipped with a low temperature chamber compatible with originally designed cryostat intended for measurements in stationary magnetic fields up to 5 T at 10 ÷ 300 K and helium combi cryostat (bath + continuous flow) for all kinds of X-ray measurements in temperature region 10 ÷ 300 K (sample in vacuum).
• Universal X-ray unit "УРС-55А".