Nonmagnetic Compound Research Articles

Tuning charge density wave of kagome metal ScV6Sn6

Compounds with a kagome lattice exhibit intriguing properties and the charge density wave (CDW) adds an additional layer of interest to research on them. In this study, we investigate the temperature and magnetic field dependent electrical properties under a chemical substitution and hydrostatic pressure of ScV6Sn6, a non-magnetic CDW compound. Substituting 5% Cr at the V site or applying 1.5 GPa of pressure shifts the CDW from 92 K to ∼ 50 K. This shift is attributed to the movement of the imaginary phonon band, as revealed by the phonon dispersion relation. The longitudinal and Hall resistivities respond differently under these stimuli. The magnetoresistance (MR) retains its quasilinear behavior under pressure, but it becomes quadratic after Cr substitution. The anomalous Hall-like behavior of the parent compound persists up to the respective CDW transition under pressure, after which it decreases sharply. In contrast, the longitudinal and Hall resistivities of Cr substituted compounds follow a two-band model and originate from the multi carrier effect. These results clearly highlight the role of phonon contributions in the CDW transition and call for further investigation into the origin of the anomalous Hall-like behavior in the parent compound.

Investigation of electronic, elastic, dynamical, thermodynamic and thermoelectric properties of Cobalt based half-Heusler compounds

Heusler compounds have attracted remarkable attention from scientists over the year by virtue of their peculiarity and suitability in multi-functional applications. In the current study, the structural, elastic, dynamical, thermodynamic and thermoelectric properties of CoMSb (M = V, Nb and Ta) half-Heusler compounds were computed. Projector augmented-wave (PAW) pseudopotentials with PBE exchange correlation functional have been used to obtain the results for the studied compounds. The computed elastic constants satisfy the general stability condition based on the cubic symmetry and endorse the ductile nature of the compounds. The CoVSb compound is predicted to be ferromagnetic half-metallic compound while CoNbSb and CoTaSb are non-magnetic compounds. The dynamical properties revealed the dynamical stability in CoVSb and CoTaSb compounds while the imaginary frequency observed at W⟶L⟶Γ predicts instability in CoNbSb compound. The thermodynamic properties for the compounds were reported. The thermoelectric properties were calculated based on the results obtained from electronic structure using semi-classical Boltzmann theory. The ductile nature and the figure of merit computed predict CoMSb (M = V, Nb and Ta) are relatively good for thermoelectric application.

The study of electronic structure and magnetic properties of ferromagnetic Kondo-lattice CePd2P2 from the first-principles

The electronic structure of ferromagnetic CePd2P2 Kondo lattice crystallizing in the tetragonal ThCr2Si2-type structure is investigated by means of the Density Functional Theory (DFT) and Time-Depedent DFT (TDDFT) methods. The calculated electronic properties from DFT are presented and compared to those of the non-magnetic LaPd2P2 compound. The differences in the FS topologies upon changing magnetic states (paramagnetic → ferromagnetic) is also examined. Including the relativistic effects of without or with spin-orbit coupling, and Hubbard corrections in the calculations, ferromagnetic ground state with an ordered magnetic moment of ∼ 0.8-0.9 μB is corroborated. Meaningful changes in the magnetic moment and electronic properties of CePd2P2 are discussed in terms of effects brought by the Coulomb interaction (U), and the Hund coupling (J). In particular, the reduction in magnetic moment and simultaneously enhancement of DOS at the Fermi energy due to decreasing J are in quantitative concordance with the Kondo lattice characteristic. Furthermore, dynamical model used in TDDFT calculations exhibits that 4 f electrons in CePd2P2 tend to be delocalized. The frequency-temperature behavior of response function allows to estimate the Kondo temperature to amount 19 K.

Enhancing Interfacial Ferromagnetism and Magnetic Anisotropy of CaRuO3/SrTiO3 Superlattices via Substrate Orientation.

Artificial oxide heterostructures have provided promising platforms for the exploration of emergent quantum phases with extraordinary properties. One of the most interesting phenomena is the interfacial magnetism formed between two non-magnetic compounds. Here, a robust ferromagnetic phase emerged at the (111)-oriented heterointerface between paramagnetic CaRuO3 and diamagnetic SrTiO3 is reported. The Curie temperature is as high as ≈155K and the saturation magnetization is as large as ≈1.3µB per formula unit for the (111)-CaRuO3/SrTiO3 superlattices, which are obviously superior to those of the (001)-oriented counterparts and are comparable to the typical itinerant ferromagnet SrRuO3. A strong in-plane magnetic anisotropy with six-fold symmetry is further revealed by the anisotropic magnetoresistance measurements, presenting a large in-plane anisotropic field of 3.0-3.6T. More importantly, the magnetic easy axis of the (111)-oriented superlattices can be effectively tuned from 〈 1〉 to 〈 〉 directions by increasing the layer thickness of SrTiO3. The findings demonstrate a feasible approach to enhance the interface coupling effect by varying the stacking orientation of oxide heterostructures. The tunable magnetic anisotropy also shows potential applications in low-power-consumption or exchange spring devices.

Local symmetry breaking and low-energy continuum in K2ReCl6

Using polarization selective spontaneous Raman scattering, we have investigated the $5d$ transition metal compound ${\mathrm{K}}_{2}{\mathrm{ReCl}}_{6}$ which displays a series of structural phase transitions. We observe a violation of the Raman selection rules in the cubic high temperature phase as well as a low-energy scattering continuum persistent throughout the investigated temperature range from 300 down to 5 K. The continuum couples to one of the phonon modes at temperatures above the lowest structural phase transition at 76 K. We propose a common origin of these observations caused by disorder in the orientation of the ${\mathrm{ReCl}}_{6}$ octahedra which locally breaks the long-range cubic symmetry. Consistent results from the related nonmagnetic compound ${\mathrm{K}}_{2}{\mathrm{SnCl}}_{6}$ support this interpretation.

Cluster-glass freezing and antiferromagnetic phase transitions in corundum structure Mg3−xCoxTeO6

We investigate polycrystalline powder samples of the Co-substituted Mg3−xCoxTeO6 (x = 0.0–2.4) by X-ray diffraction, magnetic susceptibilities, and specific heat. The non-magnetic parent compound Mg3TeO6 crystallizes in the trigonal R3¯ space group. All Co-substituted samples have a similar crystal structure as the parent compound. The Rietveld refinements of synchrotron X-ray diffraction data reveal distorted (Mg/Co)O6 and TeO6 octahedra. Remarkably, we find the evolution of a magnetic phase from a non-magnetic ground state to an antiferromagnetic order through a cluster glass. The antiferromagnetically ordered state emerges above the percolation threshold (x ≥ 1.0), while the cluster glass state is stabilized for x = 0.8.

Giant magnetoresistance in the crystalline YCd6 intermetallic compound

Giant magnetoresistance (GMR) in bulk nonmagnetic compounds has received considerable attention since this phenomenon challenged the classical understanding of electron transport under a magnetic field. Here, we report magnetotransport properties of the diamagnetic intermetallic compound ${\mathrm{YCd}}_{6}$ for applied magnetic fields up to 35 T and temperatures down to 0.4 K that reveal GMR. We argue that the large MR value can be explained in terms of field-induced pseudogaps on a Fermi surface. These results are relevant to the understanding of the Fermi-surface topology of quasicrystal approximants.

Magnetic field induced transition in the charge-glass former θ−(BEDT−TTF)2CsCo(SCN)4

We perform thermodynamic and transport measurements on a magnetic charge-glass former, $\ensuremath{\theta}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}\mathrm{CsCo}{(\mathrm{SCN})}_{4}$, to discuss the $\ensuremath{\pi}\ensuremath{-}d$ interaction occurring in the interlayer direction. An anomalous temperature dependence and sharp peak structure of the heat capacity are observed in magnetic fields, indicating a field-induced transition in this compound. Furthermore, a sharp peak of the thermoelectric power is also observed in magnetic fields, supporting the presence of the field-induced transition. Comparison with a nonmagnetic analog compound indicates that the introduction of magnetic ${\mathrm{Co}}^{2+}$ ions $(S=3/2)$ triggers this transition. This strongly suggests that the $\ensuremath{\pi}\ensuremath{-}d$ interaction effectively works in this compound and affects the physical properties. To explain the field-induced phenomenon in this compound, we propose a speculative scenario in which the $\ensuremath{\pi}\ensuremath{-}d$ interaction between the $\ensuremath{\pi}$ spins in the insulating domains and the $d$ spin of ${\mathrm{Co}}^{2+}$ induces the reconstruction of the domain structure in the CG state.

Tunable surface magnetism by gate voltage in a slab of nonmagnetic half-Heusler compound CoTiSb.

The electrical manipulation of magnetization is appealing to the relevant experiment and spintronic device. In this paper, we focus on the electrical and magnetic properties of a thin film cleaved from the nonmagnetic half-Heusler compound CoTiSb. By means of the first-principles calculations, we find that the surface of TiSb termination possesses ferrimagnetism with a magnetic moment of 0.35 (0.49) μB per unit cell without (with) Hubbard U, which can persist below the Curie temperature of 48 (54) K. What is more, such a surface magnetism can be tuned to nonmagnetism by gate-induced hole doping with a concentration of 2.83 × 1014 (3.55 × 1014) cm-2. This magnetic tunability of the CoTiSb slab provides a platform to realize the pseudo-spin valve with both the magnetic electrodes and nonmagnetic space layer made of the same material without hetero-interfaces.

Ab initio investigations of a CoBiS monolayer with and without point defects.

Through density functional theory (DFT) calculations, a new triclinic monolayer, namely CoBiS, with higher stability than that of penta-CoBiS, is predicted. Our results show that this monolayer is a nonmagnetic metallic compound. To tune its magnetic properties, we systematically investigated the formation and energetics of different point defects in the CoBiS monolayer, such as VBi, VS and VCo. We find that the monolayer becomes magnetic with the different points defects. Our calculated magnetic anisotropy energy (MAE) indicated that VBi and VS exhibit out-of-plane MAE, while the MAE is in-plane for VCo. By solving the Heisenberg model using the Monte Carlo simulation method, we obtain transition temperatures for VS and VCo systems much larger than room temperature, implying potential applications in spintronic devices.

Topological superconductivity and large spin Hall effect in the kagome family Ti6X4 (X = Bi, Sb, Pb, Tl, and In)

Topological superconductors (TSC) become a focus of research due to the accompanying Majorana fermions. However, the reported TSC are extremely rare. Recent experiments reported kagome TSC AV3Sb5 (A= K, Rb, and Cs) exhibit unique superconductivity, topological surface states (TSS), and Majorana bound states. More recently, the first titanium-based kagome superconductor CsTi3Bi5 with nontrivial topology was successfully synthesized as a perspective TSC. Given that Cs contributes little to electronic structures of CsTi3Bi5 and binary compounds may be easier to be synthesized, here, by first-principle calculations, we predict five stable nonmagnetic kagome compounds Ti6X4 (X= Bi, Sb, Pb, Tl, and In) which exhibit superconductivity with critical temperature Tc= 3.8 K 5.1 K, nontrivial band topology, and TSS close to the Fermi level. Additionally, large intrinsic spin Hall effect is obtained in Ti6X4, which is caused by gapped Dirac nodal lines due to a strong spin-orbit coupling. This work offers new platforms for TSC and spintronic devices.

FORMATION OF COMPOSITE COATINGS WITH MAGNETIC PROPERTIES IN AN ELECTROMAGNETIC FIELD

The article presents and analyzes the results of the study of the influence of a constant magnetic field on the electrodeposition processes of the ferrum family metals and their alloys. The studies performed indicate the effect of accelerating deposition, improving the surface morphology and hardness of the obtained coatings. Composite coatings applied under the influence of a constant magnetic field can have higher corrosion resistance, improved photocatalytic and magnetic properties than those obtained without it. It has been established that the presence of a constant magnetic field changes the chemical composition of the studied material. There is an increase in the ferromagnetic and a decrease in the diamagnetic component. To assess the magnetic properties, samples of Fe-Co-W and Fe-Co-Mo coatings deposited by unipolar pulsed current at different electrolysis durations were selected, which is due to the difference in the thickness and distribution of the components. The results obtained suggest that in the nonequilibrium process of electrodeposition in three-component alloys, clusters with a short-range order characteristic of a number of intermetallic nonmagnetic compounds are formed, which leads to a decrease in the saturation magnetization of the alloy. The Fe-Co-W coatings are characterized by higher values of the coercive force compared to amorphous alloys, in which the elements P, B, Si act as a non-magnetic component. Probably, for the Fe-Co-W alloy, large clusters with a compositional order similar to the arrangement of atoms in the paramagnetic intermetallic phase with tungsten, along with surface roughness and free volume, play a significant role in magnetization reversal. The results obtained make it possible to classify the obtained Fe-Co-W galvanic alloys as magnetically hard, and Fe-Co-Mo as magnetically soft materials, which, in combination with high microhardness, opens up prospects for the use of such systems in the production of magnetic elements for recording and reproducing information and microelectromechanical systems respectively. With properly designed field structures, new magnetic nanostructures and a new level of control over industrial catalytic and electroplating processes can be created.

Disorder driven variations in magnetoresistance and planar Hall effect in Bi2Te3 thin films

The degenerately doped sesquichalcogenide Bi2Te3, a well-known thermoelectric material, has attracted much attention in recent years as a topological insulator in which conducting surface states lead to exotic electronic transport. Here we report the observation of anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) in polycrystalline thin films of Bi2Te3 over a broad range of temperature and magnetic field strength. The values of AMR, PHE and the Hall mobility (μH) are compared with results of similar measurements on single crystals and epitaxial films of Bi2Te3, where these properties are understood in the framework of electronic transport in the topologically protected conducting surface states. Our textured polycrystalline films show a robust metallic character with a carrier density (ns) and mobility μH of 9×1020 cm−3 and 16.7 cm2V−1s−1 respectively. This carrier density is higher and the mobility lower by an order of magnitude compared to the reported values of ns and μH in epitaxial films and single crystals. However, we see a comparable AMR and PHE in our films for which the concept of conducting surface states is ill-defined due to their polycrystallinity and disordered structure. We suggest that an anisotropic backscattering of charge carriers in the strongly spin – orbit coupled electronic states of this heavy-metal-based non-magnetic compound may lead to the measured resistivity anisotropy. The observation of AMR and PHE in polycrystalline films may be important for scalable production of Bi2Te3 based AMR and PHE sensors of magnetic fields.

Anisotropic large magnetoresistance and Fermi surface topology of terbium monoantimonide

Rare-earth monopnictides have received a great deal of attention for their exotic magnetic and electronic properties. Here, we grow high-quality TbSb single crystals, and perform their magnetization, specific heat and transport measurements, and band structure calculations. In this compound, an antiferromagnetic phase transition emerges at ∼14.5 K (TN), below which metamagnetic behaviors can be observed. Specific heat data suggest that Γ4 triplet state dominates the ground magnetic properties, and thus gives rise to weak magnetic anisotropy. Analogous to other isostructural counterparts, TbSb shows extreme magnetoresistance and triangular temperature-field phase diagram. Hall resistivity measurements reveal that carrier concentrations and mobilities change their values in different magnetic states. These findings are supported by the theoretical calculations from which the effect of magnetic orderings on Fermi surface topology can be determined. Nevertheless, the magnetoresistance below and above TN in TbSb shares similar angle dependences, and follows the fashions as observed in those nonmagnetic sister compounds because of its weak anisotropy in magnetization. Our studies uncover the spin ordering effects on angular magnetoresistance and electronic band structures of TbSb, and could be employed to understand the related issues in other systems with similar magnetic behaviors.

Chemically and electrically tunable spin polarization in ferroelectric Cd-based hybrid organic-inorganic perovskites

Density functional theory computations are used to predict the electronic structure of Cd-based hybrid organic-inorganic high-${T}_{C}$ ferroelectric perovskites with TMCM-${\mathrm{CdCl}}_{3}$ being one representative. We report Rashba-Dresselhaus spin splitting in the valence band of these nonmagnetic compounds. Interestingly, we find in computations that the splitting is not necessarily sensitive to the polarization of the material but to the organic molecule itself which opens a way to its chemical tunability through the choice of the molecule. Further chemical tunability of spin splitting is shown to be possible through a substitution of Cl in the ${\mathrm{CdCl}}_{3}$ chains as the valence band was found to originate from Cl-Cl weekly bonding orbitals. For example, the substitution of Cl with Br in TMCM-${\mathrm{CdCl}}_{3}$ resulted in a ten times increase of spin splitting. Furthermore, the spin polarization in these materials gives origin to persistent spin textures which are coupled to the polarization direction, and, therefore, can be controlled by the electric field. This is promising for spintronics applications.

Role of f-electrons in determining insulator to metal phase transitions of Ca(La1−xCex)2S4 (0 ≤ x ≤ 1) solid solution: A DFT + U study

For efficient usage of the rare earth-based materials in electronic or optoelectronic applications, their 4f electrons' behaviors must be understood properly. We have presented Hubbard U corrected density functional theory (DFT+U) study of structural, magnetic, electronic, and optical properties of a rare-earth chalcogenide system, Ca(La1−xCex)2S4 (0 ≤ x ≤ 1). A unique site selection technique based on local magnetic moment arrangements was applied to build the atomic arrangements for a Ce doped Ca(La1−xCex)2S4 solid solution. The incorporation of f-electrons by Ce doping modifies the properties of the parent compound, CaLa2S4. In conjunction with the DFT + U method, we applied spin–orbit coupling to determine the magnetic ground state. The inclusion of 25% Ce transforms the non-magnetic parent compound to an antiferromagnetic (AFM) compound, and AFM magnetic ordering remains unaltered throughout the whole solid solution series. In addition, these compounds also undergo insulator to semiconducting to metallic phase transitions as Ce concentration increases. While CaLa2S4 is an insulator, Ca(La1−xCex)2S4 with x = 0.25 and 0.50 are n-type semiconductors, and on the other hand, compounds with x = 0.75 and 1.0 are found to have metallic band structures. The Ce atoms in these materials were found to be in a mixed valence state, Ce3+/4+. We explained these phase transitions from the calculated electronic structures. In addition, we have presented an explanation for the experimentally observed red-orange colors of Ca(La0.25 Ce0.75)2S4 and CaCe2S4 compounds.

Chemical characterization of the Bicchari ash pond and its impact around the Renusagar Thermal Power Plant, Sonbhadra district, Uttar Pradesh, India

AbstractThe Renusagar thermal power plant is one of the most important power plants supplying electricity to the entire Hindalco Industry in Northern India. This plant causes soil and groundwater contamination due to the disposal of its fly ash in the Bicchari ash pond. An attempt has been made to characterize the ash pond and to study soil and groundwater contamination adjacent to the fly ash pond. In total, 11 groundwater samples and four samples each for the ash pond and soil were collected and analyzed to evaluate the impact of the pond on nearby soil and groundwater. Results show that the pond ash is a heterogeneous mixture of magnetic and nonmagnetic (such as mullite and quartz) compounds. Scanning electron microscopy of the pond ash reveals that most of the minerals present are spheroidal in shape, and a smaller size indicates the presence of silica. X‐ray fluorescence analysis of the soils reveals that in most of the samples zircoline has a relatively higher concentration, whereas silica is the major part of SiO2. Most groundwater samples are acidic, with an average pH of 6.73, which decreases the leaching of heavy metals. The concentration of Ca, Mn, and Fe is relatively high.

A Pseudopotential Study of Structural, Mechanical, and Lattice Dynamics Behavior of the Binary Intermetallic Yttrium Tristannide YSn3

A theoretical study of many physical properties, namely structural stability, electronic, mechanical stability, and phonon properties of the nonmagnetic intermetallic compound is realized using the density functional theory (DFT) calculations. The structural properties are calculated in many phases, specifically, , , , and structures. The results show that crystallizes in the structure at ambient conditions, whereas the energy difference between the and structures is very weak and in the order of thermal energy at room temperature, which suggests the may also coexist in this structure. The single‐crystal elastic constants for different phases at zero pressure are computed, and main mechanical quantities are derived. The mechanical stability criteria predict that the crystal in the structure is stable when pressure is below 18.68 and 4.61 GPa for the and phases of . The phonon dispersion relations and their projected density of states are investigated. The titled compound is found to be dynamically and mechanically stable in the and Al3Ti prototype phases under ambient conditions. As far as the authors know, high‐pressure features of have not yet been explored neither experimentally nor theoretically.

Application of topological quantum chemistry in electrides

The recently developed theory of topological quantum chemistry (TQC) has built a close connection between band representations in momentum space and orbital characters in real space. It provides an effective way to diagnose topological materials, leading to the discovery of lots of topological materials after the screening of all known nonmagnetic compounds. On the other hand, it can also efficiently reveal spacial orbital characters, including average charge centers and site-symmetry characters. By using TQC theory with the computed irreducible representations in the first-principles calculations, we demonstrate that the electrides with excess electrons serving as anions at vacancies can be well identified by analyzing band representations (BRs), which cannot be expressed as a sum of atomic-orbital-induced band representations (aBRs). In fact, the floating bands (formed by the excess electrons) belong to the BRs induced from the "pseudo-orbitals" centered at vacancies. In other words, the electrides are proved to be unconventional ionic crystals, where a set of occupied bands is not a sum of aBRs but necessarily contains a BR from vacancies. The TQC theory provides a promising avenue to pursue more electride candidates in ionic crystals.

Direct evidence of electron-hole compensation for extreme magnetoresistance in topologically trivial YBi

The prediction of topological states in rare earth monopnictide compounds has attracted renewed interest. Extreme magnetoresistance (XMR) has also been observed in several nonmagnetic rare earth monopnictide compounds. The origin of XMR in these compounds could be attributed to several mechanisms, such as topologically nontrivial electronic structures and electron-hole carrier balance. YBi is a typical rare earth monopnictide exhibiting XMR, and expected to have a nontrivial electronic structure. In this work, we performed a direct investigation of the electronic structure of YBi by combining angle resolved photoemission spectroscopy and theoretical calculations. Our results show that YBi is topologically trivial without the expected band inversion, and they rule out the topological effect as the cause of XMR in YBi. Furthermore, we directly observed perfect electron-hole compensation in the electronic structure of YBi, which could be the primary mechanism accounting for the XMR.