arXiv subjects

Piotr Dłużewski

Publications and source records attributed to Piotr Dłużewski.

6 recordsLinked to original sources

arXiv2026

Structural properties of one-dimensional $\mathrm{Cs}_2\mathrm{CoCl}_4$ confined within single-walled carbon nanotubes

Crystals under one-dimensional (1D) confinement are well-known to exhibit drastic changes in metallicity, magnetic properties and chemical state, however, the intermediate phase space between binary metal halides and ternary metal halide perovskites remains poorly explored, especially in the context of the rich polymorphism exhibited by both families in the one-dimensional limit. Through aberration-corrected (scanning) transmission electron microscopy and multislice simulations, it is shown that the metal halide $\mathrm{Cs}_2\mathrm{CoCl}_4$ crystallizes in the tetragonal $\wp4/mcc$ and orthorhombic $\wp{mcm}$ rod groups under radial compression within single-walled carbon nanotubes (SWCNTs) of increasingly small diameter, with a massive re-entrant orthorhombic strain towards the $1$ $\mathrm{nm}$ extremum. The persistence of $\mathrm{Co}^{2+}$ is determined from fits to the d.c. magnetization, with a surprisingly small increase in the effective moment ($4.607(3)$ to $4.788(3) \mathit{μ}_\mathrm{B}/\mathrm{f.u.}$) and Weiss constant ($-7.9(3)$ to $-4.09(7) \mathrm{K}$) after confinement in the SWCNTs, suggesting that the confined structure topologically preserves the core magnetic properties of the bulk. Both unconventional polymorphs observed are noticeably different to the high-pressure piezochromic polymorph previously shown to undergo a tetrahedral-to-octahedral coordination transition, highlighting 1D confinement as a unique tool for structural manipulation.

cond-mat.mtrl-sci↗

arXiv2025

Magnetic Properties of epitaxial $\text{Re}/\text{Co}_{1-x}\text{Au}_{x}/\text{Pt}$ heterostructures

We investigate epitaxial $\text{Co}(20 \, \text{Å})$ and $\text{Co}_{1-x}\text{Au}_{x}(20 \, \text{Å})$ alloy thin-films surrounded by asymmetric heavy metals layers of $\text{Re}(10 \, \text{Å})$ as a buffer and $\text{Pt}(30 \, \text{Å})$ as a cap to study the magnetic anisotropy, interfacial Dzyaloshinskii-Moriya interaction (iDMI) and damping. The increase of Au from 0% to 25% in the $\text{Co}_{1-x}\text{Au}_{x}$ alloy generates the spin-reorientation transition of around 13% of Au. The increase in Au concentration provides a significant decrease in saturation magnetization from 1690 kA/m to 982 kA/m measured for Co and $\text{Co}_{75}\text{Au}_{25}$, respectively. The effective anisotropy constant $\text{K}_{eff}$ is elevated up to 0.33 $\text{MJ/m}^{3}$ by changing the Au content. Further, our investigations of the magnetization dynamics have confirmed that the overall effective damping constant rises with the Au concentration which can be attributed to the spin pumping effect. The spin pumping leads to the highest value of effective spin mixing conductance $g^{(\uparrow \downarrow)} \approx 2.91 \times 10^{18} \, \text{m}^{-2}$ in the $\text{Co}_{90}\text{Au}_{10}(20 \, \text{Å})$ system, while the lowest value of $g^{(\uparrow \downarrow)} \approx 2.25 \times 10^{18} \, \text{m}^{-2}$ is found for the $\text{Co}(20 \, \text{Å})$ system. Additionally, we have investigated the iDMI strength, and the amplitude of iDMI decreases with increasing Au concentration. The highest surface iDMI constant value equal to 2.62 pJ/m is observed for Co.

cond-mat.mtrl-sci↗

arXiv2024

Magnetostructural Coupling at the Néel point in YNiO3 Single Crystals

The recent discovery of superconductivity in infinite layer thin films and bulk Ruddlesden-Popper nickelates has stimulated the investigation of other predicted properties of these materials. Among them, the existence of magnetism-driven ferroelectricity in the parent compounds RNiO3 (R = 4f lanthanide and Y) at the onset of the Néel order, TN, has remained particularly elusive. Using diffraction techniques, we reveal here the existence of magnetostriction at TN in bulk YNiO3 single crystals. Interestingly, the associated lattice anomalies are much more pronounced along the b crystal axis, which coincides with the electric polarization direction expected from symmetry arguments. This axis undergoes an abrupt contraction below TN that reaches deltab/b ~ - 0.01 %, a value comparable to those found in some magnetoresistive manganites and much larger than those reported for magnetism-driven multiferroics. This observation suggests a strong spin-lattice coupling in these materials, consistent with theoretical predictions. Using the symmetry-adapted distortion mode formalism we identify the main ionic displacements contributing to the lattice anomalies and discuss the most likely polar displacements below TN. Furthermore, our data support symmetric superexchange as the most likely mechanism responsible for the magnetoelastic coupling. These results, that may be common to the full RNiO3 family, provide new experimental evidence supporting the predicted existence of magnetism-driven ferroelectricity in RNiO3 perovskites

cond-mat.str-el↗

arXiv2024

3D Topological Semimetal Phases of Strained $α$-Sn on Insulating Substrate

$α$-Sn is an elemental topological material, whose topological phases can be tuned by strain and magnetic field. Such tunability offers a substantial potential for topological electronics. However, InSb substrates, commonly used to stabilize $α$-Sn allotrope, suffer from parallel conduction, restricting transport investigations and potential applications. Here, the successful MBE growth of high-quality $α$-Sn layers on insulating, hybrid CdTe/GaAs(001) substrates, with bulk electron mobility approaching 20000 cm$^2$V$^{-1}$s$^{-1}$ is reported. The electronic properties of the samples are systematically investigated by independent complementary techniques, enabling thorough characterization of the 3D Dirac (DSM) and Weyl (WSM) semimetal phases induced by the strains and magnetic field, respectively. Magneto-optical experiments, corroborated with band structure modeling, provide an exhaustive description of the bulk states in the DSM phase. The modeled electronic structure is directly observed in angle-resolved photoemission spectroscopy, which reveals linearly dispersing bands near the Fermi level. The first detailed study of negative longitudinal magnetoresistance relates this effect to the chiral anomaly and, consequently, to the presence of WSM. Observation of the $π$ Berry phase in Shubnikov-de Haas oscillations agrees with the topologically non-trivial nature of the investigated samples. Our findings establish $α$-Sn as an attractive topological material for exploring relativistic physics and future applications.

cond-mat.mtrl-sci↗

arXiv2023

Structural pathways for ultrafast melting of optically excited thin polycrystalline Palladium films

Due to its extremely short timescale, the non-equilibrium melting of metals is exceptionally difficult to probe experimentally. The knowledge of melting mechanisms is thus based mainly on the results of theoretical predictions. This work reports on the investigation of ultrafast melting of thin polycrystalline Pd films studied by optical laser pump - X-ray free-electron laser probe experiments and molecular-dynamics simulations. By acquiring X-ray diffraction snapshots with sub-picosecond resolution, we capture the sample's atomic structure during its transition from the crystalline to the liquid state. Bridging the timescales of experiments and simulations allows us to formulate a realistic microscopic picture of melting. We demonstrate that the existing models of strongly non-equilibrium melting, developed for systems with relatively weak electron-phonon coupling, remain valid even for ultrafast heating rates achieved in femtosecond laser-excited Pd. Furthermore, we highlight the role of pre-existing and transiently generated crystal defects in the transition to the liquid state.

cond-mat.mtrl-sci↗

arXiv2019

Structural, magnetostatic and magnetodynamic studies of Co/Mo-based uncompensated synthetic antiferromagnets

In this work, we comprehensively investigate and discuss the structural, magnetostatic, dynamic, and magnetoresistive properties of epitaxial Co/Mo superlattices. The magnetization of the Co sublayers is coupled antiferromagnetically with a strength that depends on the thickness of the nonmagnetic Mo spacer. The magnetization and magnetoresistance hysteresis loops clearly reflect interlayer exchange coupling and the occurrence of uniaxial magnetic anisotropy induced by the strained Co sublayers. Upon accounting for a deviation of the sublayer thicknesses from the nominal value, theoretical modeling, including both micromagnetic and macrospin approaches, precisely reproduces experimental magnetic hysteresis loops, magnetoresistance curves, and ferromagnetic resonance dispersion relations. The Mo spacer thickness as a function of the interlayer magnetic coupling is determined as a fitting parameter by modeling the experimental results.

cond-mat.mtrl-sci↗