arXiv subjects

W. Tabiś

Publications and source records attributed to W. Tabiś.

5 recordsLinked to original sources

arXiv2024

Structure, magnetic properties, and cycloidal spin ordering in Nd-doped BiFeO$_3$ synthesized by sol-gel method

In this study, the structural and magnetic properties of Nd-doped BiFeO$_3$ materials with the formula Bi$_{1-x}$Nd$_x$FeO$_3$ $(x = 0 - 0.2)$ were investigated. Samples were prepared using the sol-gel method and annealed at 823 K for 4 hours. Microstructural studies indicated that nanomaterials with an average grain size of less than 100 nm were produced, with the smallest grain size observed for the solid solution with $x = 0.15$. Rietveld analysis of diffraction patterns revealed a composition-driven transformation from the rhombohedral $(R3c)$ lattice to the orthorhombic $(Pbam)$ structure. The above finding is correlated to Mössbauer spectroscopy data, which demonstrated the gradual destruction of the spin cycloid due to the structural transformation to the $Pbam$ structure. The spectra were analyzed using a complex hyperfine magnetic field distribution model reflecting cycloidal spin ordering. Scanning differential calorimetry revealed that for the investigated materials the magnetic ordering temperatures are close to 640 K, independently from the Nd concentration. Magnetic measurements showed the emergence of weak ferromagnetic properties with increasing Nd ions concentration, consistently with Mössbauer spectroscopy data.

cond-mat.mtrl-sci↗

arXiv2024

High-entropy magnetism of murunskite

Murunskite (K$_2$FeCu$_3$S$_4$) is a bridging compound between the only two known families of high-temperature superconductors. It is a semiconductor like the parent compounds of cuprates, yet isostructural to metallic iron-pnictides. Moreover, like both families, it has an antiferromagnetic (AF)-like response with an ordered phase occurring below $\approx$ 100 K. Through comprehensive neutron, Mössbauer, and XPS measurements on single crystals, we unveil AF with a nearly commensurate quarter-zone wave vector. Intriguingly, the only identifiable magnetic atoms, iron, are randomly distributed over one-quarter of available crystallographic sites in 2D planes, while the remaining sites are occupied by closed-shell copper. Notably, any interpretation in terms of a spin-density wave is challenging, in contrast to the metallic iron-pnictides where Fermi-surface nesting can occur. Our findings align with a disordered-alloy picture featuring magnetic interactions up to second neighbors. Moreover, in the paramagnetic state, iron ions are either in Fe$^{3+}$ or Fe$^{2+}$ oxidation states, associated with two distinct paramagnetic sites identified by Mössbauer spectroscopy. Upon decreasing the temperature below the appearance of magnetic interactions, these two signals merge completely into a third, implying an orbital transition. It completes the cascade of (local) transitions that transform iron atoms from fully orbitally and magnetically disordered to homogeneously ordered in inverse space, but still randomly distributed in real space.

cond-mat.str-el↗

arXiv2023

The impact of hydrostatic pressure, nonstoichiometry, and doping on trimeron lattice excitations in magnetite during axis switching

Trimeron lattice excitations in single crystalline magnetite, in the form of the $c$ axis switching (i.e. the reorganization of the lattice caused by external magnetic field) at temperatures below the Verwey temperature $T_V$ are observed by magnetization experiments. These excitations exhibit strong sensitivity to doping (with Zn, Al, and Ti), nonstoichiometry and hydrostatic pressure ($p < 1.2$ GPa). The considered indicators of the axis switching (AS) are: the switching field $B_{sw}$, the energy density needed to switch the axis $E_{sw}$ and the activation energy $U$. Our results show that hydrostatic pressure $p$ weakens the low$-T$ magnetite structure (decreases $T_V$) and has roughly similar effects on AS in Zn-doped Fe$_3$O$_4$ and, in much less extent, in stoichiometric magnetite. We have, however, found that while doping/nonstoichiometry also lowers $T_V$, making it more prone to temperature chaos, it drastically increases the switching field, activation and switching energies suggesting that the trimeron order, subject to change while AS occurs, is more robust. Consequently, we conclude that the manipulation of trimerons in the process of axis switching and the mechanisms leading to the Verwey transition are distinct phenomena.

cond-mat.str-el↗

arXiv2021

Arc-to-pocket transition and quantitative understanding of transport properties in cuprate superconductors

Despite immense efforts, the cuprate Fermi surface (FS) has been unambiguously determined in only two distinct, low-temperature regions of the phase diagram: a large hole-like FS at high doping, and a small electron-like pocket associated with charge-density-wave driven FS reconstruction at moderate doping. Moreover, there exists incomplete understanding of the reconstructed state, which is stabilized by high magnetic fields, and its connection with the normal state that consists of arc-like remnants of the large underlying FS. Part of the problem is that compound-specific idiosyncrasies, such as disorder effects and low structural symmetry, can obscure the fundamental properties of the quintessential CuO$_2$ planes. Here we present planar magnetotransport measurements for moderately-doped HgBa$_2$CuO$_{4+δ}$ that enable a quantitative understanding of the phase transition between the normal and reconstructed states and of the charge transport in the latter, and that demonstrate that the quasiparticle scattering rate in both states is due to Umklapp scattering. Building on prior insights, we furthermore arrive at a comprehensive understanding of the evolution of the planar transport properties throughout the entire cuprate phase diagram.

cond-mat.supr-con↗

arXiv2020

Trimeron-phonon coupling in magnetite

Using density functional theory, we study the lattice dynamical properties of magnetite (Fe$_3$O$_4$) in the high-temperature cubic and low-temperature monoclinic phases. The calculated phonon dispersion curves and phonon density of states are compared with the available experimental data obtained by inelastic neutron, inelastic x-ray, and nuclear inelastic scattering. We find a very good agreement between the theoretical and experimental results for the monoclinic $Cc$ structure revealing the strong coupling between charge-orbital (trimeron) order and specific phonon modes. For the cubic phase, clear discrepancies arise which, remarkably, can be understood assuming that the strong trimeron-phonon coupling can be extended above the Verwey transition, with lattice dynamics influenced by the short-range trimeron order instead of the average cubic structure. Our results establish the validity of trimerons (and trimeron-phonon coupling) in explaining the physics of magnetite much beyond their original formulation.

cond-mat.str-el↗