Transition metal-based layered chalcogenides show intriguing magnetic properties, high tunability, and cleavability that allow the fabrication of heterostructures with peculiar functional properties for designing spintronic devices, such as new types of low-power memory. TaFeTe2 layered van der Waals telluride can be synthesized by chemical vapor transport reactions. The optimized synthesis conditions yield bulk single crystals of the new monoclinic polymorph with unit cell parameters of a similar to 7.3 & Aring;, b similar to 6.1 & Aring;, c similar to 8.2 & Aring;, and beta similar to 93 degrees according to the indexing of the electron diffraction patterns. Study of its crystal structure using high-resolution transmission electron microscopy confirms the monoclinic distortion and indicates the presence of hexagonal Ta honeycombs and Fe-Fe dumbbells. Band structure calculations show a ferromagnetic ground state with magnetic moments of 1.5 & micro;B on Fe atoms oriented perpendicular to the structural layers. Magnetic susceptibility and magnetization measurements confirm the spin-glass state with Tf = 23 K and strong perpendicular magnetic anisotropy.

Three novel intermetallic compounds MoSb1.75Ga0.25, MoSb1.6Ge0.4, and MoSb1.6Sn0.4 of the OsGe2 structure type (C2/m space group, Pearson symbol mS12, Z = 4) have been discovered. Partial substitution of Sb by Ga, Ge, and Sn with the lower number of valence electrons allows stabilization of the crystal structure of MoSb2, which cannot be obtained under similar synthetic conditions. The Ga for Sb and Ge for Sb substitution occurs at the Sb2 crystallographic site, where short Sb2-Sb2 contacts are realized. The crystal structure of MoSb2 has a ladder-like arrangement of Mo atoms, where intracluster bonds settle in. As a result, the structure should be stable in the vicinity of 15 valence electrons per formula unit as revealed by band structure calculations. Magnetic behavior and thermoelectric properties of the new compounds were explored via thermodynamic and transport measurements. In agreement with the band structure calculations, the new compounds are metals, exhibiting relatively low thermopower.

Two platinide plumbides, Eu2Pt3Pb5 and SrPt2Pb4, were discovered using high-temperature exploratory synthesis and flux-assisted crystal growth. Their crystal structures were determined from single-crystal X-ray diffraction. Both compounds crystallize in the orthorhombic system; Eu2Pt3Pb5 belongs to the Y2Rh3Sn5 structure type (Cmc21, a = 4.6146(2) Å, b = 27.3082(12) Å, c = 7.5147(3) Å, Z = 4, R1 = 0.0310, and wR2 = 0.0736) and SrPt2Pb4 to the NdRh2Sn4 type (Pnma, a = 19.411(5) Å, b = 4.5834(13) Å, c = 7.6548(19) Å, Z = 4, R1 = 0.0399, and wR2 = 0.0906). Both compounds feature complex frameworks of Pt-Pb and Pb-Pb bonds with very similar motifs, with Eu or Sr cations filling the cavities, which differ by the presence of the TiNiSi-type EuPtPb layer in Eu2Pt3Pb5. According to the DFT calculations, both compounds are metallic and feature Sr and Eu divalent cations along with a negatively charged mostly covalent framework of Pt and Pb atoms. Magnetic measurements show that the SrPt2Pb4 compound is non-magnetic, while Eu2Pt3Pb5 is a paramagnet above ca. 85 K and below that temperature transitions to the ferromagnetically ordered state with very low coercivity.

The presented studies of resistivity (rho), thermal conductivity (kappa) and specific heat (C) at low temperature 1.8-7 K in magnetic field up to 90 kOe made it possible to detect for the first time the exponential field dependences rho(H), kappa (-1)(H), C(H) similar to exp(-mu H-eff/k(B)T) of the charge transport and thermal characteristics in the so-called antiferroquadrupole (AFQ) phase of the archetypal heavy-fermion CeB6 hexaboride. From magnetoresistance measurements it is shown that in the AFQ state the effective magnetic moment varies in the range mu(eff)(T) = 1.4-1.9 mu(B), and its value is very close to mu(eff(tau)())(T) approximate to 2 mu(B), derived from the field dependence of the relaxation time tau(H) observed in the heat capacity and thermal conductivity experiments. The phenomenological model proposed here allowes us to attribute the magnetic moments to spin droplets (ferrons), that appear in the bulk AFQ phase of CeB6 crystals. The relevant electronic phase separation at the nanoscale, manifested by dynamic charge stripes, that leads to the formation of ferrons, was revealed from the analysis of low-temperature X-ray diffraction experiments using the maximum entropy method. We argue that the Jahn-Teller collective mode of B-6 clusters is responsible for the formation of charge stripes formation inducing transverse quasi-local vibrations of pairs and triplets of Ce ions, which leads to 4f-5d spin fluctuations providing spin-polarons (ferrons) in the CeB6 matrix.

Layered chalcogenides are interesting from the point of view of the formation of two-dimensional magnetic systems for relevant applications in spintronics. High-spin Mn2+ or Fe3+ cations with five unpaired electrons are promising in the search for compounds with interesting magnetic properties. In this study, a new layered modification of the Mn2In2Se5 compound from the A2B2X5 family (“225”) was synthesized and investigated. A phase transition to the polymorph with primitive trigonal lattice was recorded at a temperature of 711 °C, which was confirmed by simultaneous thermal analysis, X-ray powder diffraction at elevated temperatures, and sample annealing and quenching. The stability of Mn2In2Se5 in air at high temperatures was investigated by thermal gravimetric analysis and powder X-ray diffraction. The new polymorph of Mn2In2Se5 crystallizes in the Mg2Al2Se5 structure type, as revealed by the Rietveld refinement against powder X-ray diffraction data. The crystal structure can be viewed as a close-packing of Se anions, in which indium and manganese cations are enclosed inside tetrahedral and octahedral voids, respectively, according to the AMnBInCBInCMnA… sequence. Magnetization measurements reveal an antiferromagnetic-like transition at a temperature of 6.3 K. The same magnetic properties are reported in the literature for the low-temperature R-centered trigonal polymorph. An approximation by the modified Curie–Weiss law yields a significant ratio of |θ|/TN = 28, which indicates strong magnetic frustration.

We show that the separation of contributions to lowtemperature heat capacity and the Hall effect, carried out in Phys. Rev. Lett. 120 257206 (2018), Nat. Phys. 15 954 (2019), Phys. Rev. X 12 021050 (2022), leads to unfounded conclusions about (i) the formation of uncharged quasiparticles (Majorana fermions) and (ii) the transition, as the magnetic field increases, to the metallic state with heavy fermions in the YbB12 semiconductor with strong electronic correlations. We obtain an alternative explanation of the experimental data in terms of the filamentary structure of conducting channels in the semiconductor matrix of ytterbium-based dodecaborides. Such channels (charge stripes) are nanoscale electron-density inhomogeneities and form manybody states near the Fermi level.

Fine details of crystal structure of archetypal CeB6 hexaboride with heavy fermions are studied at temperatures 85 and 500 K by precise X-ray diffraction technique. Small static Jahn-Teller distortions of a simple cubic lattice are observed at these temperatures, leading to emergence of (i) dynamic charge stripes along selected directions <110>, <100>, and <111> in the crystals in combination with (ii) vibrationally coupled pairs of Ce ions. Instead of a Currie-Weiss type behavior, the temperature dependence of magnetization M∼(T − TCrand)−0.8 with TCrand∼TQ∼3.3 K was deduced in a wide temperature range 5–800 K for various directions of external magnetic field, which indicates the Griffiths phase formation with nanosized clusters of magnetic ions in CeB6. Moreover, in contrast to the scenario of a single-ion Kondo lattice, when revealing the power-law behavior of the magnetic contribution ρm(T)∼T−0.4 to the resistivity in the range of 8–90 K, we conclude in favor of the regime of weak localization of charge carriers in CeB6. Fourier maps of electron density confirm the conclusion about the nanosized magnetic clusters of Ce ions in this archetypal strongly correlated electron system with unusual magnetic ground state.

A van der Waals telluride, NbFeTe2, has been synthesized using chemical vapor transport reactions. The optimized synthetic conditions yield high-quality single crystals with a novel monoclinic crystal structure. Monoclinic NbFeTe2 demonstrates a (100) cleavage plane, bulk ferromagnetism below 87 K, and a metallic ground state-the necessary prerequisites for needed spintronics technologies.

Nonmagnetic metal LuB_12 is known to exhibit considerable transport anisotropy, which was explained in literature by different mechanisms including possible formation of dynamic charge stripes below the point ∼ 150K. Here we study transport properties of solid solutions based on LuB_12 host compound with general formula R_xLu_1-xB_12 (R-Dy, Er, Tm, Yb, Lu) and with x ≤ 0.03. The experiment has been performed on single crystals of high quality in the temperature range 1.8 - 300K in magnetic fields up to 82kOe. The application of several models to the analysis of zero-field resistivity is discussed. A phenomenological description of large positive quadratic component of transverse magnetoresistance Δρ/ρ(H) = μ_D^2H^2, which dominates for all compounds under investigation, allows to estimate drift mobility exponential changes μ_D ∼ T^-α with the index α ≈ 0.95 - 1.46. In order to check the existence of additional channel of scattering, caused by probable presence of dynamic charge stripes, we performed the study of the anisotropy of magnetoresistance in Dy_0.01Lu_0.99B_12 and Tm_0.03Lu_0.97B_12 compositions including the measurements of the field scans with different current and field geometries. The data obtained allow us to confirm the fulfillment of semi-empirical Kohler's rule in a wide interval of temperatures 30 - 240K regardless of the orientation of current and magnetic field. This result was attributed as a proof of the absence of additional channel of scattering caused by stripes. We argue, that charge-transport anisotropy is originated in R_xLu_1-xB_12 due to the anisotropy of electron-phonon scattering on the one hand and the effects of Fermi surface (FS) topology (at low temperatures) on the other.

Type II superconductivity with Tc ∼ 6 K is discovered in LaB6. The critical fields are determined and the estimates for the coherence length ξ(0) ∼ 240 Å, the Ginzburg−Landau parameter κGL ∼ 2, and the electron–phonon coupling constant λe−ph ≈ 0.75 are obtained. Precision X-ray diffraction studies at T = 30 K reveal three-dimensional charge-stripe structures in LaB6. The scenario of superconductivity localized near filamentary channels with a fluctuating electron density arising in the lanthanum hexaboride matrix is discussed.

For the first time, an electronic phase transition at Tc ≈ 340 K in a classical strongly correlated electron system CeB6 is discovered and studied in detail. It is shown that the observed anomalies in the resistivity, thermal conductivity, specific heat, magnetization, and lattice parameters apparently correspond to the formation of a substructural charge density wave (s-CDW) at Tc, as well as to a change in configurations of dynamic charge stripes in this metal with electronic instability.

The broad-band reflection spectra of YB 6 and YbB 6 hexaborides with Jahn–Teller instability of the boron cage have been measured at room temperature. An optical conductivity analysis has revealed, along with the Drude electronic components, heavily overdamped collective modes, which are notable in YB 6 for high dielectric contributions, Δε = 2000–5700. The fraction of nonequilibrium charge carriers in YB 6 , which is at the boundary of structural instability in the hexaboride family, reaches 85–90%, whereas this fraction in doped YbB 6 semiconductor is not higher than 25%. It has been shown that unlike the predictions of the topological Kondo insulator model, the surface “metallization” in Yb 2+ B 6 crystals can be explained by additional doping of a surface layer with Yb 3+ ions.

The broad-band reflection spectra of YB6 and YbB6 hexaborides with Jahn–Teller instability of the boron cage have been measured at room temperature. An optical conductivity analysis has revealed, along with the Drude electronic components, heavily overdamped collective modes, which are notable in YB6 for high dielectric contributions, Δε = 2000–5700. The fraction of nonequilibrium charge carriers in YB6, which is at the boundary of structural instability in the hexaboride family, reaches 85–90%, whereas this fraction in doped YbB6 semiconductor is not higher than 25%. It has been shown that unlike the predictions of the topological Kondo insulator model, the surface “metallization” in Yb2+B6 crystals can be explained by additional doping of a surface layer with Yb3+ ions.

Magnetization M and magnetoresistance Δρρ(H,T) (MR) were studied and MR analyzed quantitatively in the complicated low temperature Néel phase of RB12 (R - Ho, Er and Tm) antiferromagnets with structural (originating from cooperative Jahn-Teller effect) and electronic (coming from dynamic charge stripes) instabilities. It is shown, that well below the Néel field (HN) the magnetoresistance is determined by the concurrence of carriers' scattering by spin-density waves (leading to a linear positive contribution Δρρ(H) ∼ H) from one side, and by ferromagnetic nanoscale clusters (leading to a linear negative MR) from the other. The development of different kind instabilities in the critical region just below HN results into the emergence of an additional negative quadratic MR term, attributed to the carriers' scattering on 4f-5d local electron density fluctuations. The anisotropy of both two linear and one quadratic MR components is analyzed in detail and compared for RB12 compounds with different magnetic structure.

Precise X-ray diffraction, heat capacity, magnetoresistance and magnetization measurements have been carried out on high quality Tm1-xYbxB12 single crystals with the goal to reconstruct the H-T and angular H-phi magnetic phase diagrams in the (110) plane of these antiferromagnets (AF) with dynamic charge stripes and Yb-ion valence instability. The analysis developed here allowed us to conclude in favor of essential changes in the filamentary structure of fluctuating charges, and the emergence and variation of stripe-induced magnetic and charge transport anisotropy that are controlled by lowering the temperature and ytterbium doping. It was found that local charge and spin fluctuations on Yb-sites suppress strongly the complicated AF state. However, the magnetic anisotropy is conserved, and the only moderate modifications of the Maltese Cross -type magnetic phase diagrams are detected in the range x < 0.2. We argue that the AF ordering of Tm3+ magnetic moments is the main factor, which determines the anisotropy in the Ne ' el phase of Tm1-xYbxB12 with carrier-mediated magnetic indirect RKKY exchange renormalized significantly by quantum fluctuations of the electron density along 110 directions. PACS: 73.22.-f, 75.47.-m, 71.27. + a.

A detailed study of charge transport in the paramagnetic phase of the cage-cluster dodecaboride Ho0.8Lu0.2B12 with an instability both of the fcc lattice (cooperative Jahn–Teller effect) and the electronic structure (dynamic charge stripes) was carried out at temperatures 1.9–300 K in magnetic fields up to 80 kOe. Four mono-domain single crystals of Ho0.8Lu0.2B12 samples with different crystal axis orientation were investigated in order to establish the singularities of Hall effect, which develop due to (i) the electronic phase separation (stripes) and (ii) formation of the disordered cage-glass state below T*~60 K. It was demonstrated that a considerable intrinsic anisotropic positive component ρanxy appears at low temperatures in addition to the ordinary negative Hall resistivity contribution in magnetic fields above 40 kOe applied along the [001] and [110] axes. A relation between anomalous components of the resistivity tensor ρanxy~ρanxx1.7 was found for H||[001] below T*~60 K, and a power law ρanxy~ρanxx0.83 for the orientation H||[110] at temperatures T < TS~15 K. It is argued that below characteristic temperature TS~15 K the anomalous odd ρanxy(T) and even ρanxx(T) parts of the resistivity tensor may be interpreted in terms of formation of long chains in the filamentary structure of fluctuating charges (stripes). We assume that these ρanxy(H||[001]) and ρanxy(H||[110]) components represent the intrinsic (Berry phase contribution) and extrinsic (skew scattering) mechanism, respectively. Apart from them, an additional ferromagnetic contribution to both isotropic and anisotropic components in the Hall signal was registered and attributed to the effect of magnetic polarization of 5d states (ferromagnetic nano-domains) in the conduction band of Ho0.8Lu0.2B12.

Angular measurements of the Hall resistivity and transverse magnetoresistance (MR) were utilized to probe at low temperatures the influence of nanoscale electronic phase separation (dynamic charge stripes) on the charge transport in single crystals of rare earth (RE) dodecaborides RB12 (R = Ho, Er, Tm, Lu). We studied several samples of every RB12 compound, each with different normal vectors n || [001], n || [110], n || [111] and n || [112] to the lateral surface of the sample, located in the same plane (1-10). The emergence of strong anisotropic components of both the Hall effect (HE), and MR was detected for all studied RB12. It turned out that the anomalies on the angular dependences of HE and MR are very similar for various RB12 with magnetic and non-magnetic RE ions, and that the amplitude of the anisotropic contributions is determined mainly by the concentration of impurities, which serve as pinning centers for the dynamic charge stripes. Depending on the charge carriers’ mobility µH in RB12 a crossover between two regimes of the anisotropic HE is observed with a threshold value µH ~ 960 cm2V-1s-1, corresponding to the mean free path [[EQUATION]], which may be attributed to some critical length of stripes in these conductors.