Main fields of research:
- Phenomenological and symmetry analyses of the ferroelastic phase transitions in the layered trigonal and rhombic crystals.
- Spontaneous and magnetic field induced Jahn -Teller type phase transitions.
- Low-energy dynamics of the layered crystal lattice and its role in the mechanisms of ferroelastic and Jahn-Teller type phase transitions at low temperatures.
- Magnetic resonance properties of low-dimensional magnets, nano- and metal-organic systems.
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The most important recent results:
- Using Raman and far-infrared spectroscopies, spontaneous ordering of the Jahn-Teller type has been observed in the rare-earth-based system KDy(MoO4)2. As it was shown, the ordering of quadrupoles in the electron subsystem is accompanied with the appearance of energy nonequivalent distortions of rare-earth ions in the ordered phase. A mean-field theory explaining the onset of a type of ordering has been constructed, which can be applied to describe the phase transitions of the Jahn-Teller type in the whole class of the rhombic crystals (A.A. Zvyagin, K. Kutko, D. Kamenskyi, A.V. Peschanskii, S. Poperezhai, N.M. Nesterenko Phys. Rev. B 98, 2018, 064406(5pp)).
- The far-infrared transmission spectra in layered systems KY(MoO4)2, KDy(MoO4)2, KEr(MoO4)2, and KTm(MoO4)2 have been measured and shown that the low energy lattice vibrations in double molybdates is well described within the quasi-one-dimensional model. The developed model describes the measured far-infrared spectra, and results of our calculations agree with previous Raman and ultrasound studies (S. Poperezhai, P. Gogoi, N. Zubenko, K. Kutko, V.I. Kutko, A.S. Kovalev, D. Kamenskyi Journal of Physics: Condensed Matter, 2017, Vol.29, p. 095402).
- The quasi-one dimensional microscopic model has been developed for describing dispersion of shear vibrational modes over the Brillouin zone in layered crystals (S.M. Poperezhai, N.S. Bondar, V.I.Kut’ko, A.S. Kovalev Fiz. Nizk. Temp, 2014, Vol.40, p. 1093).
- Raman spectroscopy investigations which permit to construct the phenomenological approaching of the ferroelastic phase transitions in the trigonal double molybdates have been added by the EPR data, and X-Ray analysis in the vicinity of the phase transition region. The new data show that the incommensurate phase is possible in the KSc(MoO4)2 (W. Zapart, M.B. Zapart, N.M. Nesterenko Ferroelectrics, 2014, 462, p. 110).
- The non-monotonic dependencies of magnetoresonance parameters in the series of the samples of multilayer system Co/Cu, in which the variable parameter is the thickness of the nonmagnetic copper layer have been found. It was found that the change of nonmagnetic copper layer thickness affects on the formation of the magnetic anisotropy of the studied system by two mechanisms. One of them is connected with changes interface roughness between magnetic and nonmagnetic layers. The second mechanism is caused by changes of pseudomorphic distortions values of the cobalt layer lattice (K. Kutko, A.I. Kaplienko, E. Nikolova et.al. Fiz. Nizk. Temp, 2009, Vol.35, p. 1114).
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Experimental equipment:
- Far-infrared spectrometer for measurements of the absorption and reflection spectra in polarized light, spectral range 10 – 200 cm-1, temperature interval 2 – 300 K.
- Spectral setup for measurements of the absorption and reflection spectra of polarized light in the spectral range 440-800 nm (range 12500 - 22500cm-1), temperature interval 1.6-300 K (optical gas cryostat)
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- Equipment for magneto-optical spectral studies (absorption, birefringence, dichroism) on the basis of the double monochromator MDR6 from temperature (interval 6 - 300 K) and magnetic field (interval ± 7 T) in the range 300-1000 nm (range 10000 – 30000 cm-1)(optical vacuum cryostat with warm windows).
- Magnetic resonance spectrometer with a resonator cavity of the appropriate frequency region 1 – 2.5 cm-1 (30 – 75 GHz), superconducting solenoid with a maximum of magnetic field 5 T, temperature interval 2 – 30 K.
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International collaboration:
- High Field Magnet Laboratory (HFML–EMFL), Radboud University, Nijmegen, The Netherlands. www
- Department of Condensed Matter Physics, Institute of Physics, Faculty of Science, Univerzita Pavla Jozefa Safarika, Kosice, Slovak Republic. www
- Institute for Low Temperature and Structure Research, Polish Academy of Science, Wroclaw, Poland. www
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We remember:
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