arXiv subjects

Petr Dolezal

Publications and source records attributed to Petr Dolezal.

4 recordsLinked to original sources

arXiv2022

Terahertz Magnetic and Lattice Excitations in van der Waals Ferromagnet VI3

We use the synergy of infrared, terahertz, and Raman spectroscopies with DFT calculations to shed light on the magnetic and lattice properties of VI3. The structural transition at TS1 = 79 K is accompanied by a large splitting of polar phonon modes. Below TS1, strong ferromagnetic fluctuations are observed. The variations of phonon frequencies at 55 K induced by magnetoelastic coupling enhanced by spin-orbit interaction indicate the proximity of long-range ferromagnetic order. Below TC = 50 K, two Raman modes simultaneously appear and show dramatic softening in the narrow interval around the temperature TS2 of the second structural transition associated with the order-order magnetic phase transition. Below TS2, a magnon in the THz range appears in Raman spectra. The THz magnon observed in VI3 indicates the application potential of 2D van der Waals ferromagnets in ultrafast THz spintronics, which has previously been considered an exclusive domain of antiferromagnets.

cond-mat.mtrl-sci↗

arXiv2022

Crystal structure evolution in the van der Waals transition metal trihalides

Most transition-metal trihalides are dimorphic. The representative chromium-based triad, CrCl3, CrBr3, CrI3, is characterized by the low-temperature phase adopting the trigonal BiI3 type while the structure of the high-temperature phase is monoclinic of AlCl3 type (C2/m). The structural transition between the two crystallographic phases is of the first-order type with large thermal hysteresis in CrCl3 and CrI3. We studied crystal structures and structural phase transitions of vanadium-based counterparts VCl3, VBr3, and VI3 by measuring specific heat, magnetization, and X-ray diffraction as functions of temperature and observed an inverse situation. In these cases, the high-temperature phase has a higher symmetry while the low-temperature structure reveals a lower symmetry. The structural phase transition between them shows no measurable hysteresis in contrast to CrX3. Possible relations of the evolution of the ratio c/a of the unit cell parameters, types of crystal structures, and nature of the structural transitions in V and Cr trihalides are discussed.

cond-mat.mtrl-sci↗

arXiv2022

Alloying driven transition between ferro- and antiferromagnetism in UTGe compounds: the UCo1-xIrxGe case

The evolution of magnetic properties of isostructural and isoelectronic solid solutions of the superconducting itinerant 5f-electron ferromagnet UCoGe with antiferromagnet UIrGe was studied by magnetization, AC susceptibility, specific heat, and electrical resistivity measurements of a series of UCo1-xIrxGe compounds in polycrystalline and single crystalline form at various temperatures and magnetic fields. Both the weak ferromagnetism and superconductivity in UCoGe were found to have vanished already for very low Ir substitution for Co x = 0.02. The antiferromagnetism of UIrGe is gradually suppressed. This is documented by a rapid decrease in both Neel temperature and the critical field of the metamagnetic transition with decreasing Ir concentration, which both tend to vanish just above x = 0.8. The section of the T-x phase diagram in the range x between 0.02 and 0.8 is dominated by a correlated paramagnetic phase exhibiting very broad bumps in temperature dependencies of b-axis magnetization and specific heat developing with increasing x. For x = 0.24, wide peaks appear in the c-axis thermomagnetic curves due to antiferromagnetic correlations which may eventually lead to frozen incoherent spin configurations at low temperatures. The correlated paramagnetic phase is also accompanied by specific electrical resistivity anomalies. The T-x phase diagram determined for the UCo1-xIrxGe compounds contrasts with the behavior of the related URh1-xIrxGe system, which was reported to exhibit an extended concentration range of stable ferromagnetism in Rh rich compounds and a discontinuous transformation between the ferromagnetic and antiferromagnetic phases at a critical Rh-Ir concentration.

cond-mat.str-el↗

arXiv2018

Local atomic arrangement in LaCuAl3 and LaAuAl3 by NMR and density functional theory

CeCuAl3 and CeAuAl3, crystallizing in the non-centrosymmetric BaNiSn3 tetragonal structure, are known mainly for their unusual neutron scattering spectra involving additional excitations ascribed to vibron quasi-bound quantum state in CeCuAl3 and anti-crossing of phonon and crystal field excitations in CeAuAl3. In this work, we present results of nuclear magnetic resonance experiments on their lanthanum analogues - LaCuAl3 and LaAuAl3. The character of nuclear magnetic resonance spectra of 139La, 27Al, and 65Cu measured in LaAuAl3 and LaCuAl3 is dominated by electric quadrupole interaction. The spectral parameters acquired from experimental data are confronted with values obtained from the electronic structure calculations. The results show remarkable diffrences for the two compounds. The 139La spectrum in LaAuAl3 can be interpreted by a single spectral component corresponding to uniform environment of La atoms in the crystal structure, whereas for LaCuAl3 the spectrum decomposition yields a wide distribution of spectral parameters, which is not possible to explain by a single La environment, and multiple non-equivalent La positions in the crystal structure are required to interpret the spectrum.

cond-mat.mtrl-sci↗