arXiv subjects

D. Repček

Publications and source records attributed to D. Repček.

3 recordsLinked to original sources

arXiv2026

THz-induced phonomagnetism in diamagnetic quantum paraelectric KTaO$_3$

The current efforts striving to develop new ways of data manipulation are aimed at ultrafast control of magnetization in magnetic materials, as well as at inducing magnetic moments in diamagnetics. We demonstrate that in the diamagnetic quantum paraelectric KTaO$_3$, the electric field of circularly polarized THz pulses with an amplitude of $\sim 300\,$kV/cm induces a transient magnetic-like response by resonantly exciting its degenerate soft polar phonon. This phonon-mediated response was measured using the THz pump---optical probe technique via the time-resolved magneto-optic Faraday effect. Our detection scheme was set up to cancel out the major part of the electro-optic Kerr effect which also usually significantly contributes to the transient response. The Kerr-effect-related signal was further suppressed by subtracting the experimental data related to oppositely circularly polarized THz radiation. Thus, we were able to unambiguously identify a temperature-dependent magnetic-like behavior of the KTaO$_3$ crystal manifested by the extracted Faraday rotation. We developed a theoretical model describing well quantitatively the measured curves of the transient Faraday effect signal. However, their amplitudes exhibit an unexpected temperature dependence, which might be a key to a deeper understanding of the observed phonomagnetic effect.

cond-mat.mtrl-sci↗

arXiv2024

A frustrated antipolar phase analogous to classical spin liquids

The study of magnetic frustration in classical spin systems was motivated by the prediction and discovery of classical spin liquid states. These uncommon magnetic phases are characterized by a massive degeneracy of their ground state implying a finite magnetic entropy at zero temperature. While the classical spin liquid state was originally predicted in the Ising triangular lattice antiferromagnet in 1950, this state has never been experimentally observed in any triangular magnets. We report here the discovery of an electric analogue of classical spin liquids on a triangular lattice of uniaxial electric dipoles in EuAl12O19 . This new type of frustrated antipolar phase is characterized by a highly degenerate state at low temperature implying an absence of long-range antiferroelectric order, despite short-range antipolar correlations. Its dynamics are governed by a thermally activated process, slowing down upon cooling towards a complete freezing at zero temperature.

cond-mat.str-el↗

arXiv2024

Microwave magnetic excitations in U-type hexaferrite Sr$_4$CoZnFe$_{36}$O$_{60}$ ceramics

Microwave (MW) transmission, absorption, and reflection loss spectra of the ferrimagnetic U-type hexaferrite Sr$_4$CoZnFe$_{36}$O$_{60}$ ceramics were studied from 100 MHz to 35 GHz at temperatures between 10 and 390 K. 9 MW magnetic excitations with anomalous behavior near the ferrimagnetic phase transitions were revealed. They also change under the application of weak bias magnetic field (0 - 700 Oe) at room temperature. 6 pure magnetic modes are assigned to dynamics of the magnetic domain walls and inhomogeneous magnetic structure of the ceramics, to the natural ferromagnetic resonance (FMR) and to the higher-frequency magnons. Three modes are considered as the magnetodielectric ones with dominating influence of the magnetic properties on their temperature and field dependences. Presence of the natural FMR in all ferrimagnetic phases proves existence of the non-zero internal magnetization and magnetocrystalline anisotropy. Splitting of the FMR into the two components without magnetic bias was observed in the collinear phase and is attributed to a change of the magnetocrystalline anisotropy during the phase transition. The high-frequency FMR component critically slows down to the phase transition. At room temperature, the FMR splitting and essential suppression of the higher-frequency modes was revealed under the weak bias field (300 - 700 Oe). The highly nonlinear MW response and the FMR splitting are caused by the gradual evolution of the polydomain magnetic structure to a monodomain one. The high number of magnetic excitations observed in the MW region confirms the suitability of using hexaferrite Sr$_4$CoZnFe$_{36}$O$_{60}$ ceramics as MW absorbers, shielding materials and highly tunable filters.

cond-mat.mtrl-sci↗