We present a comprehensive experimental and theoretical study of the electronic and magnetic properties of two quasi-two-dimensional (2D) honeycomb lattice monoclinic compounds $A_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6(A=\mathrm{Li},\mathrm{Na})$. Magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long-range order with Néel temperatures of ∼14 and 16 K for $\mathrm{L}{\mathrm{i}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6$ and $\mathrm{N}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6$, respectively. The effective magnetic moments of $4.3{\mu }_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.\left(\mathrm{L}{\mathrm{i}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6\right)$ and $4.4{\mu }_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.\left(\mathrm{N}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6\right)$, where f.u. is formula units, indicate that $\mathrm{N}{\mathrm{i}}^{2+}$ is in a high-spin configuration ($S=1$). The temperature dependence of the inverse magnetic susceptibility follows the Curie-Weiss law in the high-temperature region and shows positive values of the Weiss temperature, $\sim 8\mathrm{K}$ ($\mathrm{L}{\mathrm{i}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6$) and ∼12 K ($\mathrm{N}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6$), pointing to the presence of nonnegligible ferromagnetic interactions, although the system orders antiferromagnetically at low temperatures. In addition, the magnetization curves reveal a field-induced (spin-flop type) transition below $T_{\mathrm{N}}$ that can be related to the magnetocrystalline anisotropy in these systems. These observations are in agreement with density functional theory calculations, which show that both antiferromagnetic and ferromagnetic intralayer spin exchange couplings between $\mathrm{N}{\mathrm{i}}^{2+}$ ions are present in the honeycomb planes, supporting a zigzag antiferromagnetic ground state. Based on our experimental measurements and theoretical calculations, we propose magnetic phase diagrams for the two compounds.

Bauxite residue (BR), also known as red mud, is a byproduct of the alumina production using the Bayer process. This material is not used to make iron or other iron-containing products worldwide, owing to its high content of sodium oxide and other impurities. In this study, we investigated the hydrochemical conversion of goethite (FeOOH) to magnetite (Fe₃O₄) in high-iron BR from the Friguia alumina refinery (Guinea) by Fe²⁺ ions in highly concentrated alkaline media. The simultaneous extraction of Al and Na made it possible to obtain a product containing more than 96% Fe₃O₄. The results show that the magnetization of Al-goethite and Al-hematite accelerates the dissolution of the Al from the iron mineral solid matrix and from the desilication product (DSP). After ferrous sulfate (FeSO₄·7H₂O) was added directly at an FeO:Fe₂O₃ molar ratio of 1:1 at 120 °C for 150 min in solution with the 360 g L⁻¹ Na₂O concentration, the alumina extraction ratio reached 96.27% for the coarse bauxite residue size fraction (Sands) and 87.06% for fine BR obtained from red mud. The grade of iron (total iron in the form of iron elements) in the residue can be increased to 69.55% for sands and 58.31% for BR. The solid residues obtained after leaching were studied by XRD, XRF, TG-DTA, VSM, Mössbauer spectroscopy, and SEM to evaluate the conversion and leaching mechanisms, as well as the recovery ratio of Al from various minerals. The iron-rich residues can be used in the steel industry or as a pigment.

We have fabricated a $\mathrm{p–n}$ heterojunction diode by vapor depositing a thin film of polyaniline on top of the crystalline copolymer: poly(vinylidene fluoride with trifluoroethylene). The formation of a diode is expected from the band offsets of the two polymers near the Fermi level. The interface between the two components was investigated, and an abrupt interface was found that is very different from the inorganic analog.

Ti₃C₂T_x MXene is one of the most comprehensively studied 2D materials in terms of its adsorptive, transport, and catalytic properties, cytotoxic performance, etc. Still, conventional MXene synthesis approaches provide low single-flake MXene yield and frequently uncontrollable properties, demanding further post-processing. The MXene family also lacks magnetism, which is helpful for producing effective nanoadsorbents as their magnetic decantation is the cheapest and most convenient way to remove the spent adsorbent from water. Composite materials consisting of magnetic nanoparticles grown on top of MXene flakes are commonly used to provide magnetic properties to the resulting nanocomposite. In this paper, we study the possibility to delaminate multilayer Ti₃C₂T_x MXene sheets directly by growing iron oxide magnetic nanoparticles inside their interlayer spacing. We find out that, with a mass fraction of particles comparable or exceeding that of MXenes, their growth is accompanied by an effective enhancement of single-layer MXene yield and suitable magnetic properties of the resulting composite. The developed approach can be further used for simplifying synthesis protocols to obtain magnetic MXene-based nanoadsorbents with tunable properties.

“Ampoule in ampoule” design to grow single crystals of FeSe_1−xS_x.

The field and temperature dependencies of the resistivity and Hall effect are measured for FeSe 1 − x S x ( x = 0.04, 0.09, and 0.19) single crystals. Sample FeSe 0.81 S 0.19 does not show a transition to an orthorhombic phase and at low temperatures exhibits transport properties, which are very different from those of orthorhombic samples. The behavior of FeSe 0.81 S 0.19 is well described by the simple two-band model with comparable values of the hole and electron mobilities. The characteristics of the low-temperature transport properties of the orthorhombic Fe(SeS) samples are largely determined by the presence of a small number of highly mobile carriers, which may originate from the local regions of the Fermi surface, presumably, nearby the Van Hove singularity points. Our results, for the first time, demonstrate a strong evolution of a tiny band of highly mobile electrons at a tetragonal to orthorhombic quantum phase transition. The behavior of this band can be the reason for the diverging nematic susceptibility, determined from elastoresistivity, which is considered one of the most intriguing phenomena in the physics of iron-based superconductors.