arXiv subjects

Dalibor Repček

Publications and source records attributed to Dalibor Repček.

5 recordsLinked to original sources

arXiv2026

The effect of fluorine or chlorine substitution on mesomorphic properties of ferroelectric nematic liquid crystals

Ferroelectric nematic phase (NF) represents an attractive and foremost field of liquid crystals, combining fluidity with ferroelectricity. NF materials exhibit large polarization values and remarkable non-linear optical properties. We have designed an original molecular structure with halogen substituents in the position of an electron donating group. In a prolonged molecular core, such a modification led to the presence of the ferroelectric nematic phase (NF) below the nematic one. Besides, an application of Cl atom in the molecular core of one of the presented materials has been utilized for the first time for ferroelectric nematogens. We have examined mesogenic behaviour and ferroelectric characteristics of the NF phase. In the NF phase for the cell with antiparallel rubbing, we have detected a textural transformation, which evidences strong polar character of anchoring at the surfaces. The presented results provide valuable insight into the design of ferroelectric nematic liquid crystalline compounds.

cond-mat.soft↗

arXiv2025

Polar Nematic Phases with Enantiotropic Ferro- and Antiferroelectric Behavior

The recent discovery of a new ferroelectric nematic (NF) liquid crystalline phase became of utmost interest for the liquid crystal (LC) and the whole soft and condensed matter fields. Contrary to the previously known ferroelectric LC materials, whose ferroelectric characteristics were much weaker, new polar nematics exhibit properties comparable to solid ferroelectrics. This discovery brought about tremendous efforts to further explore compounds showing these phases, and fascinating physical properties have been reported. Herein, we present the first synthesized compounds with the enantiotropic ferro- (NF) and antiferroelectric (NX) nematic phases. The enantiotropic nature and an unprecedentedly broad temperature range of NF and NX phases are confirmed by various experimental techniques: polarized-light optical microscopy (POM) observations, different scanning calorimetry (DSC), dielectric spectroscopy, second harmonic generation (SHG), and molecular modeling. The presented achievements in designing achiral compounds that exhibit enantiotropic polar nematic phases with ferro- and antiferroelectric properties significantly contribute to the development of multicomponent mixtures with a broad temperature range of NF and NX phases down to room temperature. Furthermore, this accomplishment considerably enhances the general understanding of the structural correlations that promote polar nematic liquid crystal phases with high thermodynamic stability. Finally, this work may benefit various applications in photonic devices.

cond-mat.soft↗

arXiv2024

Weak-field FMR and magnetization near the collinear to conical ferrimagnetic phase transition in the U-type hexaferrite Sr4CoZnFe36O60 ceramics

Temperature evolution of the ferromagnetic resonance (FMR) and its interference with other microwave (MW) magnons near the collinear to conical ferrimagnetic phase transition at Tc2 = 305 K is found to correlate with the evolution of the weak-field magnetization: from two components in the conical phase to one component in the collinear phase. The FMR splitting above Tc2 correlates with the splitting of the coercive fields of the two magnetization components. A high sensitivity of the FMR to the weak magnetic bias near Tc2 is shown to be caused by the gradual transformation of the conical spin magnetic moments to the longitudinal ones. Application of the weak magnetic bias allows to adjust the MW absorption, and its level of above 30 dB is achieved near the FMR frequency (5.7 - 7.2 GHz), that allows to consider the Sr4CoZnFe36O60 hexaferrite ceramics as a possible MW absorbing material.

cond-mat.mtrl-sci↗

arXiv2024

Multiferroic quantum criticality in (Eu,Ba,Sr)TiO$_3$ solid solution

Based on the earlier published theory (\textit{Nature Mat}. \textbf{18}, 223--228 (2019)), a comprehensive experimental investigation of multiferroic quantum critical behavior of (Eu,Ba,Sr)TiO$_3$ polycrystalline and single crystal samples was performed. Presence of the displacive ferroelectric quantum criticality is revealed through non-classical ($T^2$) temperature scaling of inverse dielectric susceptibility up to 60\,K. With increasing hydrostatic pressure, this ferroelectric quantum criticality is gradually suppressed. Inverse magnetic susceptibility follows classical Curie-Weiss law down to 4 K, but quantum fluctuations belonging to an antiferromagnetic phase transition ($T_{\mathrm{N}} < 0.8$ K) change its scaling below 3 K to $T^{(1.7\pm 0.1)}$ and $T^{(2.1\pm 0.2)}$ for samples containing 29\,\% and 25\,\% of Eu$^{2+}$ ions, respectively. Experimental indications of the coexisting ferroelectric and antiferromagnetic, i.e. multiferroic, quantum fluctuations and qualitative explanation why they could be seen only in the immediate proximity of $T_{\mathrm{N}}$ is given.

cond-mat.mtrl-sci↗

arXiv2023

Dimethylamino terminated ferroelectric nematogens revealing high permittivity

Since the recent discoveries, ferroelectric nematics became of upmost interest due to their outstanding ferroelectric properties. In this work, we prepared a series of polar molecules revealing a ferroelectric nematic phase (NF) with a very high dielectric constant (>104). A new motif, which differs from previously reported molecular structures, was optimized to support the NF phase. For all homologues the NF phase was observed directly on the cooling from the isotropic phase and ferroelectric behaviour was investigated by dielectric spectroscopy, second harmonic generation, polarization current measurements and by analysis of textures in the polarized light. The presented materials combine ferroelectricity with giant permittivity in a fluid media at room temperatures, so they appear to be extremely attractive. Polarity of molecules with the strong susceptibility to the electric field represent high potential for various applications in energy-efficient memory devices or capacitors.

physics.app-ph↗