arXiv subjects

Karolina Gornicka

Publications and source records attributed to Karolina Gornicka.

14 recordsLinked to original sources

arXiv2026

Anisotropic magnetism and Kondo-lattice behavior in the frustrated antiferromagnet Ce3MgBi5

We report the synthesis and physical characterization of single-crystalline Ce3MgBi5, a previously unexplored member of the Ce3MPn5 family. This compound crystallizes in the hexagonal P63/mcm structure, featuring an anisotropic Ce sublattice composed of zig-zag chains along the c axis and a distorted kagome-like network in the basal plane. Magnetization measurements reveal antiferromagnetic order below TN approximately 4.2 K, accompanied by strong magnetic anisotropy and multiple field-induced metamagnetic transitions for fields applied perpendicular to [001], leading to a dome-shaped H-T phase diagram. Electrical transport exhibits characteristic signatures of a Ce-based Kondo lattice, including broad resistivity maxima and pronounced field-dependent anomalies in the magnetoresistance and Hall response that track the magnetic phase boundaries. Specific-heat measurements confirm the magnetic transition and show that the full R ln 2 entropy expected for a Ce3+ Kramers doublet is recovered by 20 K, indicating an extended temperature range of magnetic fluctuations consistent with Kondo correlations. Our results establish Ce3MgBi5 as a platform within the Ce3MPn5 family for exploring the interplay of geometric frustration, magnetic anisotropy, and Kondo-lattice physics under applied magnetic fields.

cond-mat.str-el↗

arXiv2026

Magnetism of single crystalline breathing pyrochlore spinel AgInCr4S8

Single crystals of \ce{AgInCr4S8} were grown by chemical vapor transport and crystallographic ordering of Ag/In that results in a breathing pyrochlore motif of Cr$^{3+}$ was verified by x-ray and neutron diffraction. Long-range antiferromagnetic order is observed below a Néel temperature of $T_{\mathrm N}$ $\approx$ 9.6 K. The magnetic properties are characterized using ac and dc magnetization, specific heat capacity, and single crystal neutron diffraction measurements. The specific heat data are characterized by a small lambda anomaly near 9.5 K and the estimated magnetic entropy reaches $\approx$ $\frac{1}{3}$ of the expected value by 3$T_{\mathrm N}$, suggesting significant short-range order in the paramagnetic phase. Single crystal neutron diffraction evidences an incommensurate spin structure with propagation vector $\textbf{\textit{k}}$ = (0,0,$δ$) and $δ$ = 0.343 at 5 K. The minimal model that accounts for the data consists of ferromagnetic layers of Cr atoms, with magnetic moments lying in the plane of the layers and modulating in the perpendicular direction to form a helical structure propagating along $\textbf{\textit{k}}$. This study represents a rare investigation of single crystals within the family of breathing pyrochlore materials.

cond-mat.str-el↗

arXiv2026

Synergistic doping and stabilization of magnetically tunable LnTi$_3$(Sb,Sn)$_4$ (Ln:Ce--Gd) kagome metals

Here we present our synthesis and characterization of the LnTi$_3$(Sb,Sn)$_4$ (Ln: Ce, Pr, Nd, Sm, Gd) family of cleavable kagome metals. While these materials are isostructural to the LnTi$_3$Bi$_4$ family, they only form as (Sb,Sn) solid-solutions with no corresponding LnTi$_3$Sb$_4$ or LnTi$_3$Sn$_4$ phases. We use a combination of first-principles density functional theory (DFT) and Crystal Orbital Hamilton Population (COHP) calculations to show that (Sb,Sn) alloying has a stabilizing effect on the structure by adjusting the Fermi level, filling bonding states, depopulating antibonding states, and adjusting the density-of-states (DOS) towards local minima, an effect we call ``synergistic doping.'' The tunable Fermi level also has a profound effect on the magnetism, which we demonstrate through a detailed characterization of the SmTi$_3$(Sb,Sn)$_4$ series. The series hosts multiple magnetic ground states resulting from competing magnetic interactions that are tunable by the (Sb,Sn) ratio. While the focus of this work is on SmTi$_3$(Sb,Sn)$_4$, we briefly comment on the (Sb,Sn) solubility range and the conferred magnetic tunability in the other rare-earths compounds (Ln: Ce, Pr, Nd, Gd) as well. Our work demonstrates how the (Sb,Sn) synergistic pair can be used to stabilize the LnTi$_3$(Sb,Sn)$_4$ structure while simultaneously providing a means to tune the magnetism, ultimately providing a potential route to develop new intermetallics with chemical, magnetic, and electronic tunability.

cond-mat.str-el↗

arXiv2025

Isolated spin ladders in Ln$_2$Ti$_9$Sb$_{11}$ (Ln:La-Nd) metals

Here we present the discovery and characterization of a series of antimonides Ln$_2$Ti$_9$Sb$_{11}$ (Ln: La--Nd) which exhibit well-isolated, $n=2$ rare-earth spin ladders. We discuss the structure of the new compounds, with a particular focus on the magnetic Ln spin ladders. Nd$_2$Ti$_9$Sb$_{11}$ and Ce$_2$Ti$_9$Sb$_{11}$ exhibit antiferromagnetic interactions and a well-defined doublet ground state, whereas Pr$_2$Ti$_9$Sb$_{11}$ exhibits a weakly magnetic singlet ground state. Nd$_2$Ti$_9$Sb$_{11}$ is a poor metal with an electrical resistivity of 0.1m$Ω$-cm at 300K and weak temperature dependence. The thermal conductivity along the ladder exhibits significant field dependence even at 40K, considerably higher than the magnetic ordering temperature of 1.1K. Compared to compounds with transition metal spin ladders, the rare-earth elements impart much lower energy scales, making these compounds highly tunable with external stimuli like magnetic fields. The diverse magnetism of the rare-earth ions and RKKY interactions further contribute to the potential for a wide array of rich magnetic ground states, positioning these materials as a rare example of an inorganic square spin-ladder platform.

cond-mat.str-el↗

arXiv2025

Anisotropic magnetism of polymorphic ErAl3

ErAl$_3$ can form in either a trigonal ($α$) or cubic ($β$) polymorph and this paper investigates the physical properties of these polymorphs through characterizations of single crystals grown in an aluminum flux. We demonstrate that polymorph selection can be achieved based on the nominal composition of the crystal growth. Magnetic measurements confirm that both $β$-ErAl$_3$ and $α$-ErAl$_3$ order antiferromagnetically at low temperatures. $β$-ErAl$_3$ undergoes AFM ordering at a Néel temperature T$_N$ = 5.1 K, and the transition is suppressed continually with applied field. $α$-ErAl$_3$ displays more complex behavior, with successive magnetic transitions at T$_N$ = 5.7 K and T$_2$ = 4.6 K for zero field, where heat capacity and dilatometry measurements evidence that these transitions are second- and first-order, respectively. Under magnetic field, strong anisotropy is revealed in $α$-ErAl$_3$, with several step-like metamagnetic transitions observed below T$_2$ for H$\parallel$c. These transitions produce sequential magnetization plateaus near one-half of the apparent saturation magnetization. The electrical resistivity of $α$-ErAl$_3$ is strongly coupled to its magnetism. At $T$ = 2 K, we observe a positive magnetoresistance reaching 60\%, with distinct anomalies at the metamagnetic transitions. The results are summarized in $H$- $T$ phase diagrams that demonstrate complex magnetic behavior for $α$-ErAl$_3$, suggesting an important role of competing interactions in this metallic system that possesses characteristics of Ising physics.

cond-mat.str-el↗

arXiv2025

Discovery of the Type-II Superconductor Ta$_4$Rh$_2$C$_{1-δ}$ with a High Upper Critical Field

We report on the discovery of superconductivity in the previously unknown compound Ta$_4$Rh$_2$C$_{1-δ}$. Ta$_4$Rh$_2$C$_{1-δ}$ crystallizes in the $η$-carbide structure type, in the cubic space group $Fd\bar{3}m$ (No.227) with a unit cell parameter of $a = $ 11.7947 Å. Temperature-dependent magnetic susceptibility, resistivity, and specific heat capacity measurements reveal that Ta$_4$Rh$_2$C$_{1-δ}$ is a type-II bulk superconductor with a critical temperature of $T_{\rm c}$ = 6.4 K, and a normalized specific heat jump $ΔC/γT_{\rm c}$ = 1.56. Notably, we find Ta$_4$Rh$_2$C$_{1-δ}$ has a high upper critical field of $μ_0 H_{\rm c2}{\rm (0)}$ = 17.4 T, which is exceeding the BCS weak coupling Pauli limit of $μ_0 H_{\rm Pauli}$ = 11.9 T.

cond-mat.supr-con↗

arXiv2025

Ferromagnetism and structural phase transition in rhombohedral PrIr3

The synthesis, structural, magnetic, thermal and transport properties are reported for polycrystalline PrIr3. At room temperature PrIr3 displays the rhombohedral space group R-3m and a PuNi3- type structure. At around 70 K a phase transition to a monoclinic C2/m structure is observed and continued cooling reveals temperature independent behavior of the unit cell volume. Further, PrIr3 undergoes a paramagnetic to ferromagnetic transition with T_C = 7.5 K. The temperature dependent magnetic susceptibility follows the Curie Weiss law with a positive Curie-Weiss temperature, and an effective moment that is close to the theoretical effective moment for a free Pr+3 ion. This introduces further complexity into the behavior of PuNi3 - type materials and highlights the importance of temperature-dependent structural studies to complement physical property measurements in intermetallic compounds.

cond-mat.mtrl-sci↗

arXiv2024

Magnetism in EuAlSi and the Eu1-xSrxAlSi Solid Solution

The magnetic properties of EuAlSi, a compound comprising a honeycomb lattice of Al and Si atoms and a triangular lattice of Eu atoms, are presented. Moreover, we have prepared the Eu1-xSrxAlSi solid solution, to study the evolution of the collective quantum properties from the ferromagnetic EuAlSi towards the superconducting SrAlSi. A possible quantum critical point is suggested to exist in the vicinity of to x of 0.96, at which the suppression of ferromagnetic order is concomitant with the emergence of superconductivity.

cond-mat.str-el↗

arXiv2024

Intricate magnetic landscape in antiferromagnetic kagome metal TbTi$_3$Bi$_4$ and interplay with Ln$_{2-x}$Ti$_{6+x}$Bi$_9$ (Ln: Tb-Lu) shurikagome metals

Here we present the discovery and characterization of the kagome metal TbTi$_3$Bi$_4$ in tandem with a new series of compounds, the Ln$_{2-x}$Ti$_{6+x}$Bi$_9$ (Ln: Tb-Lu) shurikagome metals. We previously reported on the growth of the LnTi$_3$Bi$_4$ (Ln: La-Gd$^{3+}$, Eu$^{2+}$, Yb$^{2+}$) family, a chemically diverse and exfoliable series of kagome metals with complex and highly anisotropic magnetism. However, unlike the La-Gd analogs, TbTi$_3$Bi$_4$ cannot be synthesized by our previous methodology due to phase competition with Ln$_{2-x}$Ti$_{6+x}$Bi$_9$ (x$\sim$1.7-1.2). Here we discuss the phase competition between the LnTi$_3$Bi$_4$ and Ln$_{2-x}$Ti$_{6+x}$Bi$_9$ families, helping to frame the difficulty in synthesizing LnTi$_3$Bi$_4$ compounds with small Ln species and providing a strategy to circumvent formation of Ln$_{2-x}$Ti$_{6+x}$Bi$_9$. Detailed characterization of the magnetic and electronic transport properties on single crystals of TbTi$_3$Bi$_4$ reveals a highly complex landscape of magnetic phases arising from an antiferromagnetic ground state. A series of metamagnetic transitions creates at least 5 unique magnetic phase pockets, including a 1/3 and 2/3 magnetization plateau. Further, the system exhibits an intimate connection between the magnetism and magnetotransport, exhibiting sharp switching from positive (+40%) to negative magnetoresistance (-50%). Like the LnTi$_3$Bi$_4$ kagome metals, the Ln$_{2-x}$Ti$_{6+x}$Bi$_9$ family exhibits quasi-2D networks of titanium and chains of rare-earth. We present the structures and some basic magnetic properties of the Ln$_{2-x}$Ti$_{6+x}$Bi$_9$ family alongside our characterization of the newly discovered TbTi$_3$Bi$_4$.

cond-mat.mtrl-sci↗

arXiv2021

Group-9 Transition Metal Suboxides Adopting the Filled-Ti$_2$Ni Structure: A Class of Superconductors Exhibiting Exceptionally High Upper Critical Fields

The Ti$_2$Ni and the related $η$-carbide structure are known to exhibit various intriguing physical properties. The Ti$_2$Ni structure with the cubic space group $Fd\bar{3}m$ is surprisingly complex, consisting of a unit cell with 96 metal atoms. The related $η$-carbide compounds correspond to a filled version of the Ti$_2$Ni structure. Here, we report on the structure and superconductivity in the $η$-carbide type suboxides Ti$_4$M$_2$O with M = Co, Rh, Ir. We have successfully synthesized all three compounds in single phase form. We find all three compounds to be type-II bulk superconductors with transition temperatures of $T_{\rm c}$ = 2.7, 2.8, and 5.4 K, and with normalized specific heat jumps of $ΔC/γT_{\rm c}$ = 1.65, 1.28, and 1.80 for Ti$_4$Co$_2$O, Ti$_4$Rh$_2$O, and Ti$_4$Ir$_2$O, respectively. We find that all three superconductors, exhibit high upper-critical fields. Particularly noteworthy is Ti$_4$Ir$_2$O with an upper critical field of $μ_0 H_{\rm c2}{\rm (0)}$ =~16.06~T, which exceeds by far the weak-coupling Pauli limit of 9.86~T. The role of the void filling light atom X has so far been uncertain for the overall physical properties of these materials. Herein, we have successfully grown single crystals of Ti$_2$Co. In contrast to the metallic $η$-carbide type suboxides Ti$_4$M$_2$O, we find that Ti$_2$Co displays a semimetallic behavior. Hence, the octahedral void-filling oxygen plays a crucial role for the overall physical properties, even though its effect on the crystal structure is small. Our results indicate that the design of new superconductors by incorporation of electron-acceptor atoms may in the Ti$_2$Ni-type structures and other materials with crystallographic void position be a promising future approach. The remarkably high upper critical fields, in this family of compounds, may furthermore spark significant future interest.

cond-mat.supr-con↗

arXiv2021

Superconductivity with High Upper Critical Field in the Cubic Centrosymmetric $η$-Carbide Nb$_4$Rh$_2$C$_{1-δ}$

The upper critical field is a fundamental measure of the strength of superconductivity in a material. It is also a cornerstone for the realization of superconducting magnet applications. The critical field arises because of the Copper pair breaking at a limiting field, which is due to the Pauli paramagnetism of the electrons. The maximal possible magnetic field strength for this effect is commonly known as the Pauli paramagnetic limit given as $μ_0 H_{\rm Pauli} \approx 1.86{\rm [T/K]} \cdot T_{\rm c}$ for a weak-coupling BCS superconductor. The violation of this limit is only rarely observed. Exceptions include some low-temperature heavy fermion and some strongly anisotropic superconductors. Here, we report on the superconductivity at 9.75 K in the centrosymmetric, cubic $η$-carbide-type compound Nb$_4$Rh$_2$C$_{1-δ}$, with a normalized specific heat jump of $ΔC/γT_{\rm c} =$ 1.64. We find that this material has a remarkably high upper critical field of $μ_0 H_{\rm c2}{\rm (0)}$ =~28.5~T, which is exceeding by far its weak-coupling BCS Pauli paramagnetic limit of $μ_0 H_{\rm Pauli}$~=~18.1 T. Determination of the origin and consequences of this effect will represent a significant new direction in the study of critical fields in superconductors.

cond-mat.supr-con↗

arXiv2021

Polytypism and Superconductivity in the NbS$_2$ System

We report on the phase formation and the superconducting properties in the NbS$_2$ system. Specifically, we have performed a series of standardized solid-state syntheses in this system, which allow us to establish a comprehensive synthesis map for the formation of the two polytypes 2H-NbS$_2$ and 3R-NbS$_2$, respectively. We show that the identification of two polytypes by means of X-ray diffraction is not always unambiguous. Our physical property measurements on a phase-pure sample of 3R-NbS$_2$, on a phase-pure sample of 2H-NbS$_2$, and a mixed phase sample confirm earlier reports that 2H-NbS$_2$ is a bulk superconductor and that 3R-NbS$_2$ is not a superconductor above $T =$ 1.75 K. Our results clearly show that specific heat measurements, as true bulk measurements, are crucial for the identification of superconducting materials in this and related systems. Our results indicate that for the investigation of van-der-Waals materials great care has to be taken on choosing the synthesis conditions for obtaining phase pure samples.

cond-mat.supr-con↗

arXiv2020

Superconductivity in Metal-Rich Chalcogenide Ta2Se

The metal-metal bond in metal-rich chalcogenide is known to exhibit various structures and dominate interesting physical properties. Ta2Se can be obtained by both arc-melting and solid-state pellet methods. Ta2Se crystallizes a layered tetragonal structure with space group P4/nmm (S.G.129, Pearson symbol tP6). Each unit cell consists of four layers of body-centered closed packing Ta atoms sandwiched between two square nets of Se atoms, forming the Se-Ta-Ta-Ta-Ta-Se networks. A combined result of magnetic susceptibility, resistivity, and heat capacity measurements on Ta2Se indicate the bulk superconductivity with Tc = 3.8 (1) K. According to the first-principal calculations, the d orbitals in Ta atoms dominate the Fermi level in Ta2Se. The flat bands at gamma-point in the Brillouin zone (BZ) yield to the van Hove singularities in density of states (DOS) around the Fermi level, which is intensified by introducing spin-orbit coupling (SOC) effect, thus, could be critical for the superconductivity in Ta2Se. The physical properties especially superconductivity is completely different from Ta-rich alloys or transition metal dichalcogenide TaSe2.

cond-mat.supr-con↗

arXiv2019

Observation of topological surface state in a superconducting material

The discovery of topological insulator phase has ignited massive research interests in novel quantum materials. Topological insulators with superconductivity further invigorate the importance of materials providing the platform to study the interplay between these two unique states. However, the candidates of such materials are rare. Here, we report a systematic angle-resolved photoemission spectroscopy (ARPES) study of a superconducting material CaBi2 [Tc = 2 K], corroborated by the first principles calculations. Our study reveals the presence of Dirac cones with a topological protection in this system. Systematic topological analysis based on symmetry indicator shows the presence of weak topological indices in this material. Furthermore, our transport measurements show the presence of large magnetoresistance in this compound. Our results indicate that CaBi2 could potentially provide a material platform to study the interplay between superconductivity and topology.

cond-mat.mes-hall↗