arXiv subjects

J. Zázvorka

Publications and source records attributed to J. Zázvorka.

4 recordsLinked to original sources

arXiv2026

Stress-induced Martensitic transformation in epitaxial Ni-Mn-Ga thin films and its correlation to optical and magneto-optical properties

The optical and magneto-optical properties of thin epitaxial Ni-Mn-Ga films, with thicknesses ranging from 8 to 160 nm, were investigated across the spectral range of 0.7-6.4 eV. The films were deposited by DC magnetron sputtering on MgO substrate with stress-mediating Cr buffer layer. Structural and magnetic characterization revealed an stress-induced martensitic transformation for the films thicker than 80 nm, while thinner films remained in austenite structure deformed by substrate constraint. Both X-type and Y-type twin domains were observed in martensitic samples. Magneto-optical polar Kerr effect spectra showed notable evolution with film thicknesses, demonstrating changes in electronic structure of Ni-Mn-Ga. A combination of spectroscopic ellipsometry and magneto-optical Kerr spectroscopy allowed for the deduction of the spectral dependence of full permittivity tensor of investigated samples. Three magneto-optical transitions were fitted to the spectra of non-diagonal permittivity using semiclassical theory, showing strong correlations with in-plane coercivity. Observed correlations highlight the impact of substrate-induced strain on Ni-Mn-Ga films and provide insights into the electronic structure changes associated with the martensitic transformation.

cond-mat.mtrl-sci↗

arXiv2026

Spin-to-charge-current conversion in altermagnetic candidate RuO$_2$ probed by terahertz emission spectroscopy

Using the THz emission spectroscopy, we investigate ultrafast spin-to-charge current conversion in epitaxial thin films of the altermagnetic candidate RuO$_2$. We perform a quantitative analysis of competing effects that can contribute to the measured anisotropic THz emission. These include the anisotropic inverse spin splitter and spin Hall effects in RuO$_2$, the anisotropic conductivity of RuO$_2$, and the birefringence of the TiO$_2$ substrate. We observe that the leading contribution to the measured signals comes from the anisotropic inverse spin Hall effect, with an average spin-Hall angle of $2.4\times 10^{-3}$ at room temperature. In comparison, a possible contribution from the altermagnetic inverse spin-splitter effect is found to be approximately $2-4\times 10^{-4}$. Our work stresses the importance of carefully disentangling spin-dependent phenomena that can be generated by the unconventional altermagnetic order, from the effects of the relativistic spin-orbit coupling.

cond-mat.mes-hall↗

arXiv2022

Room temperature weak collinear ferrimagnet with symmetry driven, large intrinsic magneto-optic signatures

Here we present a magnetic thin film with a weak ferrimagnetic (FIM) phase above the Néel temperature ($T_{N}$ = 240 K) and a non-collinear antiferromagnetic (AFM) phase below, exhibiting a small net magnetisation due to strain-associated canting of the magnetic moments. A long-range ordered FIM phase has been predicted in related materials, but without symmetry analysis. We now perform this analysis and use it to calculate the MOKE spectra in AFM and FIM phases. From the good agreement between the form of the measured and predicted MOKE spectra, we propose the AFM and FIM phases share the magnetic space group C2'/m' and that the symmetry driven magneto-optic and magneto-transport properties are maximised at room temperature in the FIM phase due to the non-zero intrinsic Berry phase contribution present in these materials. A room temperature FIM phase with large optical and transport signatures, as well as sensitivity to lattice strain and magnetic field, has useful prospects for high-speed spintronic applications.

cond-mat.str-el↗

arXiv2021

The surface degradation and its impact on the magnetic properties of bulk VI_3

Despite belonging to a well-studied family of transition metal trihalides, VI_3 has received significant attention only recently. As a hard ferromagnetic van der Waals compound with a large coercivity, it attracted much attention because of its potential use in atomically thin spintronic and optoelectronic devices. However, practical exploration of VI_3 is challenging due to its instability under ambient conditions. Here, we present a comprehensive set of optical, x-ray diffraction, magnetization, and ellipsometric measurements of VI3 and demonstrate that, similarly to the related van der Waals ferromagnet CrI_3, the degradation process is accelerated by the presence of moisture. The VI_3 surface was covered by selected media commonly used in physical measurements to test its stability and lower the degradation rate three times or higher, providing practical information for experimentalists interested. The decomposition study at ambient conditions shows that the VI_3 single crystal can be used for most of the bulk, magnetization, and optical measurements without any noticeable change of physical properties, as the significant degradation appears first after ~ 2 hours of exposition as illustrated, e.g., by the evolution of the ferromagnetic T_1 and T_2 transitions. The ellipsometric measurement demonstrates that even the surface remains optically stable for at least 5 minutes.

cond-mat.mtrl-sci↗