Group of investigations in pulse magnetic field
Members of the group:
Kutko K.V., Head of the group, Candidate of Sciences (Ph.D), researcher;
Nesterenko N.M., Candidate of Sciences (Ph.D), researcher.
Savytskyi V.M., Candidate of Sciences (Ph.D), researcher.
Khrustalyov V.M., Candidate of Sciences (Ph.D), junior researcher;
The main field 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.
Low temperature studies of magnetic field induced spin-orientational phase transitions in antiferromagnets with strong magnetic anisotropy.
Experimental studies of magnetic and electric properties of multiferroic compounds under high pulsed magnetic field.
Equipment:
The pulse magnet with field strenght up to 300 kOe within the hole diameter 27 mm (copper wired multilayer coil with liquid nitrogen cooling) for magnetization (differential magnetic susceptibility) and magnetoelectric effect measurements. Magnetic field pulse diration 30 ms. Sample temperature intervals: 1,6-4,2 Ê (liquid helium), 14-20,4 Ê (liquid hydrogen).
DC superconducting magnet with field up to 6 Ò for magnetization and magnetic susceptibility measurement in the tempereture interval 1.6 - 300 K.
DC water-cooled magnet with field up to 1.5 T for magnetic properties measurements at room and helium temperatures.
The most important 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
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 are 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.
The quasi-one dimensional microscopic model has been developed for describing dispersion of shear vibrational modes over the Brillouin zone in layered crystals.
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 .
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 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.
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.
The phase (Í,Ò)-diagrams of magnetic states for LiCoPO4 in magnetic field up to 285 kOe has been constructed. The second high-field phase (H > H2) has been found to be non-centrosymmetrical with magnetoelectric response
The new high-field magnetic phase in LiCoPO4 has been found within the field interval 21-28.5 T and was showed that transition from antiferromagnetic to saturated paramagnetic state occurs through three phase transitions. The possible magnetic structures formed in LiCoPO4 in high-field phases (H > H1) are proposed within the framework of the simplified two-dimensional collinear model
The five phase transitions has been found in LiNiPO4 during pulse magnetization in the field up to 285 kOe. The phase (Í,Ò)-diagrams in magnetic field up to 285 kOe has been constructed