Search Results (26)

We present first-principles results on the electronic and magnetic properties of the cubic bulk $\beta$-phase of ${\mathrm{Fe}}_2{\mathrm{O}}_3$. Given that all Fe–Fe magnetic couplings are expected to be antiferromagnetic within this high-symmetry crystal structure, the system may exhibit some signature of magnetic frustration, making it challenging to identify its magnetic ground state. We have analyzed the possible magnetic phases of the $\beta$-phase, among which there are ferrimagnets, altermagnets, and Kramers antiferromagnets. While the $\alpha$-phase is an altermagnet and the $\gamma$-phase is a ferrimagnet, we conclude that the magnetic ground state for the bulk $\beta$-phase of ${\mathrm{Fe}}_2{\mathrm{O}}_3$ is a Kramers antiferromagnet. Moreover, we find that close in energy, there is a bulk d-wave altermagnetic phase. We report the density of states and the evolution band gap as a function of the electronic correlations. For suitable values of the Coulomb repulsion, the system is a charge-transfer insulator with an indirect band gap of 1.5 eV. More in detail, the unit cell of the $\beta$-phase is composed of $8{\mathrm{Fe}}_a$ atoms and $24{\mathrm{Fe}}_b$ atoms. The $8{\mathrm{Fe}}_a$ atoms lie on the corner of a cube, and their magnetic ground state is a G-type. This structural phase is composed of zig-zag chains ${\mathrm{Fe}}_a‐{\mathrm{Fe}}_b‐{\mathrm{Fe}}_a‐{\mathrm{Fe}}_b$ with spin configuration ↑-↑-↓-↓ along the 3 directions such that for every ${\mathrm{Fe}}_a$ atoms there are $3{\mathrm{Fe}}_b$ atoms. As the opposite to the $\gamma$-phase, the magnetic configuration between the first neighbor of the same kind is always antiferromagnetic while the magnetic configuration between ${\mathrm{Fe}}_a$ and ${\mathrm{Fe}}_b$ is ferro or antiferro. In this magnetic arrangement, first-neighbor interactions cancel out in the mean-field estimation of the Néel temperature, leaving second-neighbor magnetic exchanges as the primary contributors, resulting in a Néel temperature lower than that of other phases. Our work paves the way toward the ab initio study of nanoparticles and alloys for the $\beta$-phase of ${\mathrm{Fe}}_2{\mathrm{O}}_3$. Full article

The branched complexes of Schiff bases with various iron(III) salts, named G2-[L₂Fe]⁺A⁻ (A⁻ is NO₃⁻, Cl⁻, PF₆⁻), were synthesized using the condensation reaction between carbazole derivatives of salicylic aldehyde and N’-ethylethylenediamine and characterized by various spectroscopic methods (GPC, IR, ¹H NMR, UV/Vis). The studies revealed that the coordination of the two ligand molecules to metal occurs through the nitrogen ions and oxygen atom of azomethine to form a homoleptic system. All the synthesized coordination compounds were examined for their thermal, optical, and magnetic features. Static magnetic measurements showed that only G2-[L₂Fe]Cl was in a single-phase HS state, whereas the Fe(III) ions of G2-[L₂Fe]NO₃ and G2-[L₂Fe]PF₆ at room temperatures were in mixed low-spin (LS, S = 1/2) and high-spin (HS, S = 5/2) states: 58.9% LS/41.1% HS for G2-[L₂Fe]NO₃, 56.1% LS and 43.9% HS for G2-[L₂Fe]PF₆. All G2-[L₂Fe]⁺A⁻ complexes demonstrate antiferromagnetic exchange interactions between neighboring Fe(III) ions. The ground spin state at 2.0 K revealed a Brillouin contribution from non-interacting LS ions and a proportion of the HS Fe(III) ions not participating in AFM interactions: 57%, 18%, and 16% for G2-[L₂Fe]Cl, G2-[L₂Fe]NO₃ and G2-[L₂Fe]PF₆, respectively. EPR measurements confirmed the presence of magnetically active HS and LS states of Fe(III) ions and made it possible to distinguish two HS types-with strong low-symmetry (I-type) and weak, distorted octahedral environments (II-type). It was shown that G2-[L₂Fe]⁺A⁻ complexes are magnetically inhomogeneous and consist of two magnetic sub-lattices: AFM-correlated chains in layers from the I-type HS Fe(III) centers and dynamic short-range AFM ordered LS/II-type HS Fe(III) centers in the paramagnetic phase located between the layers. Full article

We have simulated BiCoO${}_3$ films epitaxially grown along (001) direction with density functional theory computations. Leading candidates for the lowest-energy phases have been identified. The tensile strains induce magnetic phase transition in the ground state ($P4mm$ symmetry) from a C-type antiferromagnetic order to a G-type order for the in-plane lattice parameter above 3.922 Å. The G-type antiferromagnetic order will be maintained with larger tensile strains; however, a continuous structural phase transition will occur, combining the ferroelectric and antiferrodistortive modes. In particular, the larger tensile strain allows an isostructural transition, the so-called Cowley’s ‘‘Type Zero’’ phase transitions, from $Cc$-(I) to $Cc$-(II), with a slight volume collapse. The orientation of ferroelectric polarization changes from the out-of-plane direction in the $P4mm$ to the in-plane direction in the $Pmc{2}_1$ state under epitaxial tensile strain; meanwhile, the magnetic ordering temperature T${}_N$ can be strikingly affected by the variation of misfit strain. Full article

Cobalt oxide, a multifunctional, anti-ferromagnetic p-type semiconductor with an optical bandgap of ~2.00 eV, exhibits remarkable catalytic, chemical, optical, magnetic, and electrical properties. In our study, cobalt oxide nanoparticles (Co₃O₄ NPs) were prepared by the green synthesis method using dried fruit extracts of Hyphaene thebaica (doum palm) as a cost-effective reducing and stabilizing agent. Scanning electron microscopy (SEM) depicts stable hollow spherical entities which, consist of interconnected Co₃O₄ NPs, while energy-dispersive X-ray spectroscopy (EDS) indicates the presence of Co and O. The obtained product was identified by X-ray diffraction (XRD) that showed a sharp peak at (220), (311), (222), (400), (511) indicating the high crystallinity of the product. The Raman peaks indicate the Co₃O₄ spinel structure with an average shift of Δν~9 cm⁻¹ (191~470~510~608~675 cm⁻¹). In the Fourier transform infrared spectroscopy (FT-IR) spectrum, the major bands at 3128 cm⁻¹, 1624 cm⁻¹, 1399 cm⁻¹, 667 cm⁻¹, and 577 cm⁻¹ can be attributed to the carbonyl functional groups, amides, and Co₃O₄ NPs, respectively. The photocatalytic activity of the synthesized NPs was evaluated by degrading methylene blue dye under visible light. Approximately 93% degradation was accomplished in the reaction time of 175 min at a catalyst loading of 1 g/L under neutral pH. This study has shown that Co₃O₄ is a promising material for photocatalytic degradation. Full article

The dimensions of nanoribbons have a significant impact on their material properties. In the fields of optoelectronics and spintronics, one-dimensional nanoribbons exhibit distinct advantages due to their low-dimensional and quantum restrictions. Novel structures can be formed by combining silicon and carbon at different stoichiometric ratios. Using density functional theory, we thoroughly explored the electronic structure properties of two kinds of silicon–carbon nanoribbons (penta-SiC₂ and g-SiC₃ nanoribbons) with different widths and edge conditions. Our study reveals that the electronic properties of penta-SiC₂ and g-SiC₃ nanoribbons are closely related to their width and orientation. Specifically, one type of penta-SiC₂ nanoribbons exhibits antiferromagnetic semiconductor characteristics, two types of penta-SiC₂ nanoribbons have moderate band gaps, and the band gap of armchair g-SiC₃ nanoribbons oscillates in three dimensions with the width of the nanoribbon. Notably, zigzag g-SiC₃ nanoribbons exhibit excellent conductivity, high theoretical capacity (1421 mA h g⁻¹), moderate open circuit voltage (0.27 V), and low diffusion barriers (0.09 eV), making them a promising candidate for high storage capacity electrode material in lithium-ion batteries. Our analysis provides a theoretical basis for exploring the potential of these nanoribbons in electronic and optoelectronic devices as well as high-performance batteries. Full article

In this work, we have studied structural and magnetic properties of LaFeO₃ as a function of the particle size d, from bulk (d >> 1 µm) to nanoscale (d ≈ 30 nm). A large number of twins were observed for large particles that disappear for small particle sizes. This could be related to the softening of the FeO₆ distortion as particle size decreases. It was observed that the bulk sample showed spin canting that disappeared for d ~ 125 nm and can be associated with the smoothening of the orthorhombic distortion. On the other hand, for d < 60 nm, the surface/volume ratio became high and, despite the high crystallinity of the nanoparticle, a notable exchange effect bias appeared, originated by two magnetic interactions: spin glass and antiferromagnetism. This exchange bias interaction was originated by the formation of a “magnetic core–shell”: the broken bonds at the surface atoms give place to a spin glass behavior, whereas the inner atoms maintain the antiferromagnetic G-type order. The LaFeO₃ bulk material was synthesized by the ceramic method, whereas the LaFeO₃ nanoparticles were synthesized by the sol-gel method; the particle size was varied by annealing the samples at different temperatures. The physical properties of the materials have been investigated by XRD, HRTEM, TGA, and AC and DC magnetometry. Full article

The tetranuclear iron(III) compounds [Fe₄(μ₃-O)₂(μ-L^Z)₄] (1–3) were obtained by reaction of FeCl₃ with the shortened salen-type N₂O₂ tetradentate Schiff bases N,N’-bis(salicylidene)-o-Z-phenylmethanediamine H₂L^Z (Z = NO₂, Cl and OMe, respectively), where the one-carbon bridge between the two iminic nitrogen donor atoms guide preferentially to the formation of oligonuclear species, and the ortho position of the substituent Z on the central phenyl ring selectively drives towards Fe₄ bis-oxido clusters. All compounds show a flat almost-symmetric butterfly-like conformation of the {Fe₄(μ₃-O)₂} core, surrounded by the four Schiff base ligands, as depicted by both the X-ray molecular structures of 1 and 2 and the optimized geometries of all derivatives as obtained by UM06/6-311G(d) DFT calculations. The strength of the antiferromagnetic exchange coupling constants between the iron(III) ions varies among the three derivatives, despite their magnetic cores remain structurally almost unvaried, as well as the coordination of the metal ions, with a distorted octahedral environment for the two-body iron ions, Fe_b, and a pentacoordination with trigonal bipyramidal geometry for the two-wing iron ions, Fe_w. The different magnetic behavior within the series of examined compounds may be ascribed to the influence of the electronic features of Z on the electron density distribution (EDD) of the central {Fe₄(μ₃-O)₂} core, substantiated by a Quantum Theory of Atoms In Molecules (QTAIM) topological analysis of the EDD, as obtained by UM06 calculations 1–3. Full article

Recently, a series of oxyfluorides, Sr_1−xBa_xFeO₂F with x = 0, 0.25, 0.50, and 0.75 obtained through a novel synthesis route, were characterized by X-ray and neutron powder diffraction (NPD), magnetization measurements, and ⁵⁷Fe Mössbauer spectroscopy (MS). The diffraction data revealed random occupancy of Sr and Ba atoms at the A-cation site, and a statistical distribution of O and F at the anionic sublattice of the perovskite-like structure specified in space group Pm-3m. MS spectra analysis consistently indicated the presence of Fe³⁺ ions at B-site, confirming the Sr_1−xBa_xFeO₂F stoichiometry. Magnetic structure determination from the NPD data at room temperature established G-type antiferromagnetic arrangement in all compositions with Fe³⁺ moments of about 3.5 μB oriented along the c axis. In this study, we present and analyze additional NPD data concerning the low-temperature chemical and magnetic structure of Sr_0.5Ba_0.5FeO₂F (x = 0.5) and SrFeO₂F (x = 0). Basically, the three-dimensional G-type magnetic structure is maintained down to 2 K, where it is fully developed with an ordered magnetic moment of 4.25(5) μ_B/Fe at this temperature for x = 0.5 and 4.14(3) μ_B/Fe for x = 0. The data processing is complemented with a new approach to analyze the temperature dependence of the magnetic order T_N on the lattice parameters, based on the magnetic hyperfine fields extracted from the temperature-dependent MS data. Full article

The structural, electrical, and magneto-elastic properties of lanthanide base nitride (Ln = Dy-Lu) anti-perovskites were investigated using density functional theory (DFT). The reported structural outcomes are consistent with the experiment and decrease from Dy to Lu due to the decrease ofatomic radii of Ln atoms. According to the electronic band profile, the metallic characteristics of these compounds are due to the crossing over of Ln-f states at the Fermi level and are also supported by electrical resistivity. The resistivity of these compounds at room temperature demonstrates that they are good conductors. Their mechanical stability, anisotropic, load-bearing, and malleable nature are demonstrated by their elastic properties. Due to their metallic and load-bearing nature, in addition to their ductility, these materials are suitable as active biomaterials, especially when significant acting loads are anticipated, such as those experienced by such heavily loaded implants as hip and knee endo-prostheses, plates, screws, nails, dental implants, etc. In thesecases, appropriate bending fatigue strength is required in structural materials for skeletal reconstruction. Magnetic properties show that all compounds are G-type anti-ferromagnetic, with the Neel temperatures ranging from 24 to 48 K, except Lu₃Nin, which is non-magnetic. Due to their anti-ferromagnetic structure, magnetic probes cannot read data contained in anti-ferromagnetic moments, therefore, data will be unchanged by disrupted magnetic field. As a result, these compounds can be the best candidates for magnetic cloaking devices. Full article

CuFeS₂/TiO₂ nanocomposite has been prepared by a simple, low-cost mechanochemical route to assess its visible-light-driven photocatalytic efficiency in Methyl Orange azo dye decolorization. The structural and microstructural characterization was studied using X-ray diffraction and high-resolution transmission electron microscopy. The presence of both components in the composite and a partial anatase-to-rutile phase transformation was proven by X-ray diffraction. Both components exhibit crystallite size below 10 nm. The crystallite size of both phases in the range of 10–20 nm was found and confirmed by TEM. Surface and morphological properties were characterized by scanning electron microscopy and nitrogen adsorption measurement. Scanning electron microscopy has shown that the nanoparticles are agglomerated into larger grains. The specific surface area of the nanocomposite was determined to be 21.2 m^2·g⁻¹. Optical properties using UV-Vis and photoluminescence spectroscopy were also investigated. CuFeS₂/TiO₂ nanocomposite exhibits strong absorption with the determined optical band gap 2.75 eV. Electron paramagnetic resonance analysis has found two types of paramagnetic ions in the nanocomposite. Mössbauer spectra showed the existence of antiferromagnetic and paramagnetic spin structure in the nanocomposite. The CuFeS₂/TiO₂ nanocomposite showed the highest discoloration activity with a MO conversion of ~ 74% after 120 min irradiation. This study has shown the possibility to prepare nanocomposite material with enhanced photocatalytic activity of decoloration of MO in the visible range by an environmentally friendly manner Full article

Heterometallic complexes of tetrakis(µ-carboxylato)diruthenium(II,III) with tetracyanidoaurate(III) [Ru₂(RCOO)₄Au(CN)₄]_n (R = CH₃ (1), C₂H₅ (2), i-C₃H₇ (3), and t-C₄H₉ (4)) were synthesized and characterized by C,H,N-elemental analysis and infrared spectroscopy and diffuse reflectance spectroscopy. The molecular structures were determined by a single-crystal X-ray diffraction method. A polymeric arrangement with the Ru₂(RCOO)₄⁺ units alternately linked by Au(CN)₄⁻ units is formed in these complexes. The trans-bridging mode of the Au(CN)₄⁻ unit for connecting the two Ru₂(RCOO)₄⁺ units was observed for 1 and 4, while the cis-bridging mode of the Au(CN)₄⁻ unit was observed for 2 and 3. Magnetic susceptibility data with variable temperature were modeled with a zero-field splitting model (D = 75 cm⁻¹) and the presence of weak antiferromagnetic coupling between the Ru^IIRu^III units (zJ = −0.15~−0.10 cm⁻¹) was estimated. N₂-adsorption isotherms showed Type II curves with S_BET of 0.728–2.91 m² g⁻¹. Full article

We combine theoretical and experimental X-ray absorption near-edge spectroscopy (XANES) to probe the local environment around cationic sites of bulk spinel cobalt tetraoxide (Co${}_3$O${}_4$). Specifically, we analyse the oxygen K-edge spectrum. We find an excellent agreement between our calculated spectra based on the density functional theory and the projector augmented wave method, previous calculations as well as with the experiment. The oxygen K-edge spectrum shows a strong pre-edge peak which can be ascribed to dipole transitions from O $1s$ to O $2p$ states hybridized with the unoccupied $3d$ states of cobalt atoms. Also, since Co${}_3$O${}_4$ contains two types of Co atoms, i.e., Co${}^{3+}$ and Co${}^{2+}$, we find that contribution of Co${}^{2+}$ ions to the pre-edge peak is solely due to single spin-polarized $t_{2\mathrm{g}}$ orbitals ($d_{xz}$, $d_{yz}$, and $d_{xy}$) while that of Co${}^{3+}$ ions is due to spin-up and spin-down polarized $e_{\mathrm{g}}$ orbitals ($d_{x^2-y^2}$ and $d_{z^2}$). Furthermore, we deduce the magnetic moments on the Co${}^{3+}$ and Co${}^{2+}$ to be zero and 3.00 ${\mu }_B$ respectively. This is consistent with an earlier experimental study which found that the magnetic structure of Co${}_3$O${}_4$ consists of antiferromagnetically ordered Co${}^{2+}$ spins, each of which is surrounded by four nearest neighbours of oppositely directed spins. Full article

The phase content and sequence, the crystal structure, and the magnetic properties of perovskite solid solutions of the (1−y)BiFeO₃–yBiZn_0.5Ti_0.5O₃ series (0.05 ≤ y ≤ 0.90) synthesized under high pressure have been studied. Two perovskite phases, namely the rhombohedral R3c and the tetragonal P4mm, which correspond to the structural types of the end members, BiFeO₃ and BiZn_0.5Ti_0.5O₃, respectively, were revealed in the as-synthesized samples. The rhombohedral and the tetragonal phases were found to coexist in the compositional range of 0.30 ≤ y ≤ 0.90. Magnetic properties of the BiFe_1−y[Zn_0.5Ti_0.5]_yO₃ ceramics with y < 0.30 were measured as a function of temperature. The obtained compositional variations of the normalized unit-cell volume and the Néel temperature of the BiFe_1−y[Zn_0.5Ti_0.5]_yO₃ perovskites in the range of their rhombohedral phase were compared with the respective dependences for the BiFe_1−yB³⁺_yO₃ perovskites (where B³⁺ = Ga, Co, Mn, Cr, and Sc). The role of the high-pressure synthesis in the formation of the antiferromagnetic states different from the modulated cycloidal one characteristic of the parent BiFeO₃ is discussed. Full article

In this work, we adopted pulsed laser deposition (PLD) with a Nd:YAG laser to develop Bi_1−xGd_xFeO₃ (BGFO) films on glass substrates. The phase composition, microstructure, ferroelectric, magnetic, and nanomechanical properties of BGFO films are studied. BGFO films with x = 0.00–0.15 were confirmed to mainly consist of the perovskite phase. The structure is transformed from rhombohedral for x = 0.00 to pseudo-cubic for x = 0.05–0.10, and an additional phase, orthorhombic, is coexisted for x = 0.15. With increasing Gd content, the microstructure and surface morphology analysis shows a gradual decrease in crystallite size and surface roughness. The hardness of 5.9–8.3 GPa, measured by nanoindentor, is mainly dominated by crystallized structure and grain size. Good ferroelectric properties are found for BGFO films with x = 0.00–0.15, where the largest remanent polarization (2P_r) of 133.5 µC/cm² is achieved for x = 0.10, related to low leakage and high BGFO(110) texture. The improved magnetic properties with the significant enhancement of saturation magnetization from 4.9 emu/cm³ for x = 0 to 23.9 emu/cm³ for x = 0.15 by Gd substitution is found and related to large magnetic moment of Gd³⁺ and suppressed spiral spin structure of G-type antiferromagnetism. Furthermore, we also discuss the mechanisms of leakage behavior as well as nanomechanical characterizations as a function of the Gd content. Full article

Here, we review the different series of (super)conducting and magnetic radical salts prepared with organic donors of the tetrathiafulvalene (TTF) family and oxalato-based metal complexes (ox = oxalate = C₂O₄²⁻). Although most of these radical salts have been prepared with the donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF = ET), we also include all the salts prepared with other TTF-type donors such as tetrathiafulvalene (TTF), tetramethyl-tetrathiafulvalene (TM-TTF), bis(ethylenediseleno)tetrathiafulvalene (BEST), bis(ethylenedithio)tetraselenafulvalene (BETS) and 4,5-bis((2S)-2-hydroxypropylthio)-4′,5′-(ethylenedithio)tetrathiafulvalene (DMPET). Most of the oxalate-based complexes are monomers of the type [M^III(C₂O₄)₃]³⁻, [Ge(C₂O₄)₃]²⁻ or [Cu(C₂O₄)₂]²⁻, but we also include the reported salts with [Fe₂(C₂O₄)₅]⁴⁻ dimers, [M^II(H₂O)₂[M^III(C₂O₄)₃]₂]⁴⁻ trimers and homo- or heterometallic extended 2D layers such as [M^IIM^III(C₂O₄)₃]⁻ and [M^II₂(C₂O₄)₃]²⁻. We will present the different structural families and their magnetic properties (such as diamagnetism, paramagnetism, antiferromagnetism, ferromagnetism and even long-range magnetic ordering) that coexist with interesting electrical properties (such as semiconductivity, metallic conductivity and even superconductivity). We will focus on the electrical and magnetic properties of the so-called Day series formulated as β″-(BEDT-TTF)₄[A⁺M^III(C₂O₄)₃]·G, which represents the largest family of paramagnetic metals and superconductors reported to date, with more than fifty reported examples. Full article