Anezka Bendova - Academia.edu (original) (raw)

Papers by Anezka Bendova

Journal of Physics: Condensed Matter, May 23, 2022

Most transition-metal trihalides are dimorphic. The representative chromium-based triad, CrCl3, C... more 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 lowtemperature 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.

Physical review, Jan 27, 2022

The evolution of magnetic properties of isostructural and isoelectronic solid solutions of the su... more The evolution of magnetic properties of isostructural and isoelectronic solid solutions of the superconducting itinerant 5 f-electron ferromagnet (FM) UCoGe with antiferromagnet (AFM) UIrGe was studied by magnetization, AC susceptibility, specific heat, and electrical resistivity measurements of a series of UCo 1−x Ir x Ge compounds in polycrystalline and single-crystalline form at various temperatures and magnetic fields. Both the weak FM and superconductivity in UCoGe were found to have vanished already for very low Ir substitution for Co (x = 0.02). The AFM of UIrGe is gradually suppressed. This is documented by a rapid decrease in both Néel 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 0.02 x 0.8 is dominated by a correlated paramagnetic phase (CPM) 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 AFM correlations which may eventually lead to frozen incoherent spin configurations at low temperatures. The CPM is also accompanied by specific electrical resistivity anomalies. The T-x phase diagram determined for the UCo 1−x Ir x Ge compounds contrasts with the behavior of the related URh 1−x Ir x Ge system, which was reported to exhibit an extended concentration range of stable FM in Rh-rich compounds and a discontinuous transformation between the FM and AFM phases at a critical Rh-Ir concentration. The striking difference is tentatively attributed to (a) the instability of tiny U moment in the weak itinerant FM UCoGe induced by substitutional disorder at already very low Ir doping, (b) the rather stable U moment in URhGe formed by much less delocalized 5 f electrons assisted by weakly varying lattice parameters of URh 1−x Ir x Ge compounds.

arXiv (Cornell University), Jun 28, 2021

The evolution of magnetic properties of isostructural and isoelectronic solid solutions of the su... more 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 UCo 1−x Ir x Ge 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 Néel 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 0.02  x  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 UCo 1−x Ir x Ge compounds contrasts with the behavior of the related URh 1-x Ir x Ge 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. The striking difference is tentatively attributed to a) the instability of tiny U moment in the weak itinerant ferromagnet UCoGe induced by substitutional disorder at already very low Ir doping, b) the rather stable U moment in URhGe formed by much less delocalized 5f-electrons assisted by weakly varying lattice parameters of URh 1−x Ir x Ge compounds.

arXiv (Cornell University), Mar 21, 2023

We studied magnetic states and phase transitions in the van der Waals antiferromagnet VBr3 experi... more We studied magnetic states and phase transitions in the van der Waals antiferromagnet VBr3 experimentally by specific heat and magnetization measurements of single crystals in high magnetic fields and theoretically by the density functional theory calculations focused on exchange interactions. The magnetization behavior mimics Ising antiferromagnets with magnetic moments pointing out-of-plane due to strong uniaxial magnetocrystalline anisotropy. The out-of-plane magnetic field induces a spin-flip metamagnetic transition of first-order type at low temperatures, while at higher temperatures the transition becomes continuous. The first-order and continuous transition segments in the field-temperature phase diagram meet at a tricritical point. The magnetization response to the in-plane field manifests a continuous spin canting which is completed at the anisotropy field µ0HMA  27 T. At higher fields the two magnetization curves above saturate at the same value of magnetic moment µsat  1.2 µB/f.u., which is much smaller than the spin-only (S = 1) moment of the V 3+ ion. The reduced moment can be explained by the existence of an unquenched orbital magnetic moment antiparallel to the spin. The orbital moment is a key ingredient of a mechanism responsible for the observed large anisotropy. The exact energy evaluation of possible magnetic structures shows that the intralayer zigzag antiferromagnetic order is preferred which renders the antiferromagnetic ground state significantly more stable against the spin-flip transition than the other options. The calculations also predict that a minimal distortion of the Br ion sublattice causes a radical change of the orbital occupation in the ground state, connected with the formation of the orbital moment and the stability of magnetic order. I.

Most transition-metal trihalides are dimorphic. The representative chromium-based triad, CrCl3, C... more 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 n...

Journal of Physics: Condensed Matter, May 23, 2022

Physical review, Jan 27, 2022

arXiv (Cornell University), Jun 28, 2021

The evolution of magnetic properties of isostructural and isoelectronic solid solutions of the su... more 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 UCo 1−x Ir x Ge 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 Néel 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 0.02  x  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 UCo 1−x Ir x Ge compounds contrasts with the behavior of the related URh 1-x Ir x Ge 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. The striking difference is tentatively attributed to a) the instability of tiny U moment in the weak itinerant ferromagnet UCoGe induced by substitutional disorder at already very low Ir doping, b) the rather stable U moment in URhGe formed by much less delocalized 5f-electrons assisted by weakly varying lattice parameters of URh 1−x Ir x Ge compounds.

arXiv (Cornell University), Mar 21, 2023

Most transition-metal trihalides are dimorphic. The representative chromium-based triad, CrCl3, C... more 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 n...