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- ItemNature of electrically detected magnetic resonance in highly nitrogen-doped 6H-SiC single crystals(American Physical Society, 2024-09-09) Holiatkin, Maryna; Solodovnyk, Artur; Laguta, Oleksii; Neugebauer, Petr; Kalabukhova, Ekatarina; Savchenko, DariyaThis work focuses on unraveling electron paramagnetic resonance (EPR) and electrically detected magnetic resonance (EDMR) properties of n-type 6H silicon carbide (SiC) single crystals with high concentrations of uncompensated nitrogen (N) donors, which is essential for fundamental understanding of spin-related phenomena, developing spin-based devices, optimizing materials and devices, and advancing research in quantum information and spintronics. Utilizing low-temperature multifrequency EPR spectroscopy (9.4-395.12 GHz), we identified two intense signals labeled as S line and S1 line in the 6H-SiC crystals with N D - N A approximate to 8 x 1018 and 4 x 1019 cm-3. In addition, in 6H-SiC crystals with N D - N A approximate to 8 x 1018 cm-3, a low-intensity triplet from N donors substituting the quasicubic "k2" nonequivalent position (Nk2) was observed. The S line [g perpendicular to = 2.0029(2), g|| = 2.0038(2)] was assigned to the exchange interaction of conduction electrons and Nk2, while the S1 line [g perpendicular to = 2.0030(2), g|| = 2.0040(2)] is caused by the exchange spin coupling of localized N donors at the "k1" and "k2" positions. The S1 line was observed in high-frequency EDMR spectra of 6H-SiC with N D - N A approximate to 8 x 1018 cm-3, and its emergence was explained by an enhancement of the hopping conductivity due to the EPR-induced temperature increase mechanism. No EDMR spectra were found to occur in the 6H-SiC crystals with N D - N A approximate to 4 x 1019 cm-3, which is close to the critical donor concentration value for a semiconductor-metal transition. Thus it can be concluded that this N donor concentration is too high for the appearance of spin-dependent scattering and too low for the emergence of EPR-induced hopping mechanisms in 6H-SiC.
- ItemKlein-Gordon and Schrödinger solutions in Lovelock quantum gravity(Elsevier, 2024-09-01) Bousder, Mostafa; Riadsolh, A.; El Fatimy, Abdelouahad; El Belkacemi, M.; Ez-Zahraouy, HaminThis study investigates the application of wave functions to explore various solutions of the Klein-Gordon and Schrödinger equations within the framework of Lovelock gravity. We also present the derived Smarr formula from the topological density. The Klein-Gordon solution leads to the Wheeler-de Witt Hamiltonian and quasinormal modes, and we demonstrate the connection between the potential and the black hole temperature within the Schwarzschild limit. Additionally, we discuss different solutions of the Schrödinger equation, with one solution highlighting the influence of the Airy solution on the wave function's evolution over time.
- ItemPhotoswitchable hydrazones with pyridine-based rotors and halogen substituents(ROYAL SOC CHEMISTRY, 2024-06-27) Kotásková, Lucie; Jewula, Pawel; Herchel, Radovan; Nemec, Ivan; Neugebauer, PetrThe Z,E-photoisomerization of pyridine-based hydrazone switches is typically suppressed due to the presence of pyridine-based rotors. The crystal structures of studied compounds were investigated using theoretical methods combining DFT and QT-AIM calculations to unveil the nature and properties of the intramolecular hydrogen bonding. In this study, we introduced a new series of pyridine-based hydrazones anchored with o-halogen substituents (2-X) and investigated their photoswitching abilities using 1H NMR and UV-Vis spectroscopy. The efficiency of the photoisomerization from initial 2-X-Z to the 2-X-E isomer varied, with the highest yield observed for 2-Cl-E (55%). Our findings, supported by DFT calculations, revealed the formation of a new diastereomer, 2-X-E*, upon back-photoisomerization. We demonstrated that hydrazones from the 2-X series can be reversibly photoswitched using irradiation from the UV-Vis range, and additionally, we explored the effect of the halogen atom on their switching capabilities and also on their thermodynamics and kinetics of photoswitching, determining their molecular solar thermal energy storage potential. We report on the E,Z-photoisomerization of hydrazone switches with pyridine-based rotors and halogen-substituted stators.
- ItemLattice solvent- and substituent-dependent spin-crossover in isomeric iron(ii) complexes(Royal Society of Chemistry, 2024-07-02) Senthil Kumar, Kuppusamy; Mizuno, Asato; Kämmerer, Lea; Salamon, Soma; Heinrich, Benoît; Bailly, Corinne; Šalitroš, Ivan; Wende, Heiko; Ruben, MarioSpin-state switching in iron(ii) complexes composed of ligands featuring moderate ligand-field strength-for example, 2,6-bi(1H-pyrazol-1-yl)pyridine (BPP)-is dependent on many factors. Herein, we show that spin-state switching in isomeric iron(ii) complexes composed of BPP-based ligands-ethyl 2,6-bis(1H-pyrazol-1-yl)isonicotinate (BPP-COOEt, L1) and (2,6-di(1H-pyrazol-1-yl)pyridin-4-yl)methylacetate (BPP-CH2OCOMe, L2)-is dependent on the nature of the substituent at the BPP skeleton. Bi-stable spin-state switching-with a thermal hysteresis width (Delta T-1/2) of 44 K and switching temperature (T-1/2) = 298 K in the first cycle-is observed for complex 1CH3CN composed of L1 and BF4- counter anions. Conversely, the solvent-free isomeric counterpart of 1CH3CN-complex 2a, composed of L2 and BF4- counter anions-was trapped in the high-spin (HS) state. For one of the polymorphs of complex 2bCH3CN-2bCH3CN-Y, Y denotes yellow colour of the crystals-composed of L2 and ClO4- counter anions, a gradual and non-hysteretic SCO is observed with T-1/2 = 234 K. Complexes 1CH3CN and 2bCH3CN-Y also underwent light-induced spin-state switching at 5 K due to the light-induced excited spin-state trapping (LIESST) effect. Structures of the low-spin (LS) and HS forms of complex 1CH3CN revealed that spin-state switching goes hand-in-hand with pronounced distortion of the trans-N{pyridyl}-Fe-N{pyridyl} angle (phi), whereas such distortion is not observed for 2bCH3CN-Y. This observation points that distortion is one of the factors making the spin-state switching of 1CH3CN hysteretic in the solid state. The observation of bi-stable spin-state switching with T-1/2 centred at room temperature for 1CH3CN indicates that technologically relevant spin-state switching profiles based on mononuclear iron(ii) complexes can be obtained.
- ItemSpin Crossover in Three Mononuclear Iron (III) Schiff Base Complexes(MDPI, 2019-08-02) Nemec, Ivan; Svoboda, Ingrid; Herchel, RadovanThe synthesis, crystal structure, and magnetic properties of three new mononuclear complexes [Fe(R-LA)(L1)](BPh4), where R-LA(2-) is a doubly deprotonated pentadentate Schiff base ligand and L1 is a monodentate benzimidazole or furopyridine ligand, are reported. Ligand- and anion-driven changes in crystal structures and magnetic behavior were investigated in terms of the magnetic susceptibility measurements and theoretical calculations.