Search Results (11)

We present a brief review of experimental and theoretical papers on studies of electron transport and magnetic properties in manganese-based compounds Mn₂YZ and Mn₃Z (Y = V, Cr, Fe, Co, Ni, etc.; Z = Al, Ge, Sn, Si, Pt, etc.). It has been shown that in the electronic subsystem of Mn₂YZ compounds, the states of a half-metallic ferromagnet and a spin gapless semiconductor can arise with the realization of various magnetic states, such as a ferromagnet, a compensated ferrimagnet, and a frustrated antiferromagnet. Binary compounds of Mn₃Z have the properties of a half-metallic ferromagnet and a topological semimetal with a large anomalous Hall effect, spin Hall effect, spin Nernst effect, and thermal Hall effect. Their magnetic states are also very diverse: from a ferrimagnet and an antiferromagnet to a compensated ferrimagnet and a frustrated antiferromagnet, as well as an antiferromagnet with a kagome-type lattice. It has been demonstrated that the electronic and magnetic properties of such materials are very sensitive to external influences (temperature, magnetic field, external pressure), as well as the processing method (cast, rapidly quenched, nanostructured, etc.). Knowledge of the regularities in the behavior of the electronic and magnetic characteristics of Mn₂YAl and Mn₃Z compounds can be used for applications in micro- and nanoelectronics and spintronics. Full article

Several ternary rare-earth metals containing titanium aluminum intermetallics in the RE₂TiAl₃ series (RE = Y, Gd–Lu) have been synthesized from the elements using arc-melting techniques. All compounds crystallize in the trigonal crystal system with rhombohedral space group R3m (Z = 3) and lattice parameters ranging between a = 582–570 and c = 1353–1358 pm. They adopt the Mg₂Ni₃Si-type structure, which is an ordered superstructure of the cubic Laves phase MgCu₂ and has been observed for Al intermetallics for the first time. Tetrahedral [TiAl₃] entities that are connected over all corners form a network where the empty [TiAl₃] tetrahedra exhibit a full Ti/Al ordering based on the single crystal results. The Al atoms are arranged into 6³ Kagomé nets, while the Ti atoms connect these nets over the triangular units. In the cavities of this three-dimensional arrangement, the RE cations can be found forming a distorted diamond-type substructure. Magnetic measurements revealed that Y₂TiAl₃ and Lu₂TiAl₃ are Pauli paramagnetic substances, in line with the metallic character. The other compounds exhibit paramagnetism with antiferromagnetic ordering at a maximum Néel temperature of T_N = 26.1(1) K for Gd₂TiAl₃. Full article

The connectivity and inherent frustration of the kagome lattice can produce interesting electronic structures and behaviors in compounds containing this structural motif. Here we report the properties of Pt${}_3$X${}_2$ (X = In and Tl) that adopt a double-layer kagome net structure related to that of the topologically nontrivial high-temperature ferromagnet Fe₃Sn₂ and the density wave hosting compound V₃Sb₂. We examined the structural and physical properties of single crystal Pt₃Tl₂ and polycrystalline Pt₃In₂ using X-ray and neutron diffraction, magnetic susceptibility, heat capacity, and electrical transport measurements, along with density functional theory calculations of the electronic structure. Our calculations show that Fermi levels lie in pseudogaps in the densities of states with several bands contributing to transport, and this is consistent with our Hall effect, magnetic susceptibility, and heat capacity measurements. Although electronic dispersions, characteristic of simple kagome nets with nearest-neighbor hopping, are not clearly seen, likely due to the extended nature of the Pt $5d$ states, we do observe moderately large and non-saturating magnetoresistance values and quantum oscillations in the magnetoresistance and magnetization associated with the kagome nets of Pt. Full article

Quantum fluctuations inherent in electronic systems positioned close to magnetic instabilities can lead to novel collective phenomena. One such material, $\beta$-Ti${}_6$Sn${}_5$, sits close to ferromagnetic (FM) instability and can be pushed to an itinerant FM-ordered state with only minute magnetic or non-magnetic doping. The binary nature of this compound, however, limits the tuning variables that can be applied to study any emergent physics, which are likely to be sensitive to the introduction of chemical disorder.Accordingly, we grew high-quality single crystals of a new quaternary compound Zr${}_3$V${}_3$GeSn${}_4$ from a Sn-rich self flux, and determined the structure with single-crystal X-ray diffraction. Zr${}_3$V${}_3$GeSn${}_4$ forms in an ordered derivative of the hexagonal $\beta$-Ti${}_6$Sn${}_5$ structure with Zr and V atomic positions that show no indication of site interchange. Ge likewise occupies a single unique atomic position. The V site, which would be the one most likely to give rise to any magnetic character, is located at the center of a distorted octahedron of Sn, with such octahedra arranged in face-sharing chains along the crystallographic c axis, while the chains themselves are organized in a kagome geometry. Zr${}_3$V${}_3$GeSn${}_4$ represents the second known quaternary phase within this system, suggesting that other compounds with this structure type await discovery. Full article

The kagome lattice consisting of corner-sharing triangles has been studied in the context of quantum physics for more than seventy years. For the novel discovered kagome superconductor CsV${}_3$Sb${}_5$, identifying the pairing symmetry of order parameter remained an elusive problem until now. Based on the two-band Ginzburg–Landau theory, we study the temperature dependence of upper critical field and magnetic penetration depth for this compound. All theoretical results are consistent with the experimental data, which strongly indicates the existence of two-gap s-wave superconductivity in this system. In addition, it is worth noting that the anisotropy of effective masses in the band with large (or small) gap is about 70 (or 2.4). With the calculation of the Kadowaki–Woods ratio as $0.58\times {10}^{-5}$$\mathsf{\mu }\mathsf{\Omega }\mathrm{cm}{\mathrm{mol}}^2{\mathrm{K}}^2{\mathrm{mJ}}^{-2}$, the semi-heavy-fermion feature is suggested in the compound CsV${}_3$Sb${}_5$. Full article

RV₆Sn₆ (R = Sc, Y, or rare earth) is a new family of kagome metals that have a similar vanadium structural motif as AV₃Sb₅ (A = K, Rb, Cs) compounds. Unlike AV₃Sb₅, ScV₆Sn₆ is the only compound among the series of RV₆Sn₆ that displays a charge density wave (CDW) order at ambient pressure, yet it shows no superconductivity (SC) at low temperatures. Here, we perform a high-pressure transport study on the ScV₆Sn₆ single crystal to track the evolutions of the CDW transition and to explore possible SC. In contrast to AV₃Sb₅ compounds, the CDW order of ScV₆Sn₆ can be suppressed completely by a pressure of about 2.4 GPa, but no SC is detected down to 40 mK at 2.35 GPa and 1.5 K up to 11 GPa. Moreover, we observed that the resistivity anomaly around the CDW transition undergoes an obvious change at ~2.04 GPa before it vanishes completely. The present work highlights a distinct relationship between CDW and SC in ScV₆Sn₆ in comparison with the well-studied AV₃Sb₅. Full article

A mixed-valence manganese selenite, Mn₃O(SeO₃)₃, was successfully synthesized using a conventional hydrothermal method. The three-dimensional framework of this compound is composed of an MnO₆ octahedra and an SeO₃ trigonal pyramid. The magnetic topological arrangement of manganese ions shows a three-dimensional framework formed by the intersection of octa-kagomé spin sublattices and staircase-kagomé spin sublattices. Susceptibility, magnetization and heat capacity measurements confirm that Mn₃O(SeO₃)₃ exhibits two successive long-range antiferromagnetic orderings with T_N1~4.5 K and T_N2~45 K and a field-induced spin–flop transition at a critical field of 4.5 T at low temperature. Full article

Averievite-type compounds with the general formula (MX)[Cu₅O₂(TO₄)], where M = alkali metal, X = halogen and T = P, V, have been synthesized by crystallization from gases and structurally characterized for six different compositions: 1 (M = Cs; X = Cl; T = P), 2 (M = Cs; X = Cl; T = V), 3 (M = Rb; X = Cl; T = P), 4 (M = K; X = Br; T = P), 5 (M = K; X = Cl; T = P) and 6 (M = Cu; X = Cl; T = V). The crystal structures of the compounds are based upon the same structural unit, the layer consisting of a kagome lattice of Cu²⁺ ions and are composed from corner-sharing (OCu₄) anion-centered tetrahedra. Each tetrahedron shares common corners with three neighboring tetrahedra, forming hexagonal rings, linked into the two-dimensional [O₂Cu₅]⁶⁺ sheets parallel to (001). The layers are interlinked by (T⁵⁺O₄) tetrahedra (T⁵⁺ = V, P) attached to the bases of the oxocentered tetrahedra in a “face-to-face” manner. The resulting electroneutral 3D framework {[O₂Cu₅](T⁵⁺O₄)₂}⁰ possesses channels occupied by monovalent metal cations M⁺ and halide ions X⁻. The halide ions are located at the centers of the hexagonal rings of the kagome nets, whereas the metal cations are in the interlayer space. There are at least four different structure types of the averievite-type compounds: the P-3m1 archetype, the 2 × 2 × 1 superstructure with the P-3 space group, the monoclinically distorted 1 × 1 × 2 superstructure with the C2/c symmetry and the low-temperature P2₁/c superstructure with a doubled unit cell relative to the high-temperature archetype. The formation of a particular structure type is controlled by the interplay of the chemical composition and temperature. Changing the chemical composition may lead to modification of the structure type, which opens up the possibility to tune the geometrical parameters of the kagome net of Cu²⁺ ions. Full article

We report on high-pressure synchrotron X-ray diffraction measurements on Ni₃V₂O₈ at room-temperature up to 23 GPa. According to this study, the ambient-pressure orthorhombic structure remains stable up to the highest pressure reached in the experiments. We have also obtained the pressure dependence of the unit-cell parameters, which reveals an anisotropic compression behavior. In addition, a room-temperature pressure–volume third-order Birch–Murnaghan equation of state has been obtained with parameters: V₀ = 555.7(2) ų, K₀ = 139(3) GPa, and K₀′ = 4.4(3). According to this result, Ni₃V₂O₈ is the least compressible kagome-type vanadate. The changes of the crystal structure under compression have been related to the presence of a chain of edge-sharing NiO₆ octahedral units forming kagome staircases interconnected by VO₄ rigid tetrahedral units. The reported results are discussed in comparison with high-pressure X-ray diffraction results from isostructural Zn₃V₂O₈ and density-functional theory calculations on several isostructural vanadates. Full article

The continuous substitution of tin by lead (M ${}^{\mathrm{IV}}$ ) allows for the exploration geometric criteria for the stability of the different stacking variants of alkaline-earth tri-tetrelides $A^{\mathrm{II}}{M}_3^{\mathrm{IV}}$ . A series of ternary Sr and Ba mixed tri-stannides/plumbides A ${}^{\mathrm{II}}$ (Sn ${}_{1-x}$ Pb ${}_x$ ) ${}_3$ (A ${}^{\mathrm{II}}$ = Sr, Ba) was synthesized from stoichiometric mixtures of the elements. Their structures were determined by means of single crystal X-ray data. All structures exhibit close packed ordered $A{M}_3$ layers containing M kagomé nets. Depending on the stacking sequence, the resulting M polyanion resembles the oxygen substructure of the hexagonal (face-sharing octahedra, h stacking, Ni ${}_3$ Sn-type, border compound BaSn ${}_3$ ) or the cubic (corner-sharing octahedra, c stacking, Cu ${}_3$ Au-type, border compound SrPb ${}_3$ ) perovskite. In the binary compound BaSn ${}_3$ (Ni ${}_3$ Sn-type) up to 28% of Sn can be substituted against Pb (hP8, P $6_3/$ mmc, x = 0.28(4): a = 726.12(6), c = 556.51(6) pm, R1 = 0.0264). A further increased lead content of 47 to 66% causes the formation of the BaSn ${}_{2.57}$ Bi ${}_{0.43}$ -type structure with a ${\left(\mathit{hhhc}\right)}_2$ stacking [hP32, P $6_3/$ mmc, x = 0.47(3): a = 726.80(3), c = 2235.78(14) pm, R1 = 0.0437]. The stability range of the BaPb ${}_3$ -type sequence ${\left(\mathit{hhc}\right)}_3$ starts at a lead proportion of 78% (hR36, R $\overline{3}$ m, a = 728.77(3), c = 2540.59(15) pm, R1= 0.0660) and reaches up to the pure plumbide BaPb ${}_3$ . A second new polymorph of BaPb ${}_3$ forms the Mg ${}_3$ In-type structure with a further increased amount of cubic sequences [ ${\left(\mathit{hhcc}\right)}_3$ ; hR48, a = 728.7(2), c = 3420.3(10) pm, R1 = 0.0669] and is thus isotypic with the border phase SrSn ${}_3$ of the respective strontium series. For the latter, a Pb content of 32% causes a small existence region of the PuAl ${}_3$ -type structure [hP24, P $6_3/$ mmc, a = 696.97(6), c = 1675.5(2) pm, R1 = 0.1182] with a ${\left(\mathit{hcc}\right)}_2$ stacking. The series is terminated by the pure c stacking of SrPb ${}_3$ , the stability range of this structure type starts at 75% Pb (cP4, Pm $\overline{3}$ m; a = 495.46(9) pm, R1 = 0.0498). The stacking of the close packed layers is evidently determined by the ratio of the atomic radii of the contributing elements. The Sn/Pb distribution inside the polyanion (’coloring’) is likewise determined by size criteria. The electronic stability ranges, which are discussed on the basis of the results of FP-LAPW band structure calculations are compared with the Zintl concept and Wade’s/mno electron counting rules. Still, due to the presence of only partially occupied steep M-p bands the compounds are metals exhibiting pseudo band gaps close to the Fermi level. Thus, this structure family represents an instructive case for the transition from polar ionic/covalent towards (inter)metallic chemistry. Full article

Three new hybrid inorganic-metalorganic compounds containing Keggin-type polyoxometalates, neutral copper(II)-picolinate complexes and guanidinium cations have been synthesized in bench conditions and characterized by elemental analysis, infrared spectroscopy and single-crystal X-ray diffraction: the isostructural [C(NH₂)₃]₄[{XW₁₂O₄₀}{Cu₂(pic)₄}]·[Cu₂(pic)₄(H₂O)]₂·6H₂O [X = Si (1), Ge (3)] and [C(NH₂)₃]₈[{SiW₁₂O₄₀}₂{Cu(pic)₂}₃{Cu₂(pic)₄(H₂O)}₂]·8H₂O (2). The three compounds show a pronounced two-dimensional character owing to the structure-directing role of guanidinium. In 1 and 3, layers of [{XW₁₂O₄₀}{Cu₂(pic)₄}]_n⁴ⁿ⁻ hybrid POM chains and layers of [Cu₂(pic)₄(H₂O)] complexes and [C(NH₂)₃]⁺ cations pack alternately along the z axis. The hydrogen-bonding network established by guanidinium leads to a trihexagonal tiling arrangement of all copper(II)-picolinate species. In contrast, layers of [C(NH₂)₃]⁺-linked [{SiW₁₂O₄₀}₂{Cu(pic)₂}₃]_n⁸ⁿ⁻ double chains where each Keggin cluster displays a {Cu₂(pic)₄(H₂O)} moiety pointing at the intralamellar space are observed in 2. The thermal stability of 1–3 has been studied by thermogravimetric analyses and variable temperature powder X-ray diffraction. Compounds 1 and 3 undergo single-crystal to single-crystal transformations promoted by reversible dehydration processes and the structures of the corresponding anhydrous phases 1a and 3a have been established. Despite the fact that the [Cu₂(pic)₄(H₂O)] dimeric complexes split into [Cu(pic)₂] monomers upon dehydration, the packing remains almost unaltered thanks to the preservation of the hydrogen-bonding network established by guanidinium and its associated Kagome-type lattice. Splitting of the dimeric complexes has been correlated with the electron paramagnetic resonance spectra. Full article