Charge Spin Density Research Articles

Electronic and geometric properties of M@Pt12 bimetallic clusters (M = Li, Na, K): A density functional theory

Using density functional theory, this study investigates the changes that occur to the electronic and geometric properties of alkali metals doped with Pt12 clusters. The research shows that doping causes enormous changes in the geometric structure of the clusters, which makes them stable. This is particularly noticeable for K@Pt12 clusters. This research investigates frontier molecular orbitals and finds that Li@Pt12 and Na@Pt12 clusters have small Eg of 0.13 eV and 0.19 eV, respectively, which could make them better for electronic and photovoltaic uses. Analysis of spin charge density indicates that in Li@Pt12 and Na@Pt12 clusters, the Pt12 cage contributes the most spin to the electronic structures, with little to no spin contribution from Li and Na atoms, while in K@Pt12, both the K+ ion and the Pt12 cage build up the electronic structure. Charge density analysis shows alkali metals transfer electrons to the Pt12 cage, making ionic bonds in Li@Pt12 and metallic bonds in Na@Pt12, and K@Pt12 clusters, respectively. However, density of states (DOS) shows how new electronic states are created upon doping, altering the cluster's electronic properties. Furthermore, the calculation of global reactivity descriptors indicates that doping alters the chemical reactivity and kinetic stability. Clusters of K@Pt12 show enhanced hardness and stability. The results of this research provide novel insight into Pt12 clusters doped with Li, Na, and K. Furthermore, it expands the abilities of computational chemists to design materials that propel technological advancement.

Investigation of spin excitations and charge order in bulk crystals of the infinite-layer nickelate LaNiO2

Recent x-ray spectroscopic studies have revealed spin excitations and charge density waves in thin films of infinite-layer (IL) nickelates. However, clarifying whether the origin of these phenomena is intrinsic to the material class or attributable to impurity phases in the films has presented a major challenge. Here we utilize topotactic methods to synthesize bulk crystals of the IL nickelate LaNiO2 with crystallographically oriented surfaces. We examine these crystals using resonant inelastic x-ray scattering (RIXS) at the Ni L3-edge to elucidate the spin and charge correlations in the bulk of the material. While we detect the presence of prominent spin excitations in the crystals, fingerprints of charge order are absent at the ordering vectors identified in previous thin-film studies. These results contribute to the understanding of the bulk properties of LaNiO2 and establish topotactically synthesized crystals as viable complementary specimens for spectroscopic investigations. Published by the American Physical Society 2024

Spontaneous Chirality Flipping in an Orthogonal Spin-Charge Ordered Topological Magnet

The asymmetric distribution of chiral objects with opposite chirality is of great fundamental interest ranging from molecular biology to particle physics. In quantum materials, chiral states can build on inversion-symmetry-breaking lattice structures or emerge from spontaneous magnetic ordering induced by competing interactions. Although the handedness of a chiral state can be changed through external fields, a spontaneous chirality flipping has yet to be discovered. We present experimental evidence of chirality flipping via changing temperature in a topological magnet EuAl4, which features orthogonal spin density waves (SDW) and charge density waves (CDW). Using circular dichroism of Bragg peaks in the resonant magnetic x-ray scattering, we find that the chirality of the helical SDW flips through a first-order phase transition with modified SDW wavelength. Intriguingly, we observe that the CDW couples strongly with the SDW and displays a rare commensurate-to-incommensurate transition at the chirality flipping temperature. Combining with first-principles calculations and angle-resolved photoemission spectroscopy, our results support a Fermi surface origin of the helical SDW with intertwined spin, charge, and lattice degrees of freedom in EuAl4. Our results reveal an unprecedented spontaneous chirality flipping and lay the groundwork for a new functional manipulation of chirality through momentum-dependent spin-charge-lattice interactions. Published by the American Physical Society 2024

Lattice Strained Induced Spin Regulation in Co-N/S Coordination-Framework Enhanced Oxygen Reduction Reaction.

Oxygen reduction reaction (ORR) is the bottleneck of metal-air batteries and fuel cells. Strain regulation can change the geometry and adjust the surface charge distribution of catalysts, which is a powerful strategy to optimize the ORR activity. The introduction of controlled strain to the material is still difficult to achieve. Herein, we present a temperature-pressure-induced strategy to achieve the controlled lattice strain for metal coordination polymers. Through the systematic study of the strain effect on ORR performance, the relationship between geometric and electronic effects is further understood and confirmed. The strained Co-DABDT (DABDT=2,5-diaminobenzene-1,4-dithiol) with 2 % lattice compression exhibits a superior half-wave potential of 0.81 V. Theoretical analysis reveals that the lattice strain changes spin-charge densities around S atoms for Co-DABDT, and then regulates the hydrogen bond interaction with intermediates to promote the ORR catalytic process. This work helps to understand the catalytic mechanism from the atomic level.

Electronic and magnetic properties of Au-doped diamond surfaces by first-principles calculation.

The electronic and magnetic properties of the Au-doped diamond surface are investigated by first-principles calculation. After Au-doping, diamond shows surface p-type conductivity with an areal electron density of 6.34 × 1013 cm-2. Unlike the non-magnetic feature of intrinsic diamond, magnetism is induced for diamond (100), (110) and (111) surfaces as well as at different terminations (H, F, N and O). The magnetism originates from the s-p hybridization between the Au-6s state and the C-2p state, and the spin charge density and magnetic moments of Au-doped diamond originate mainly from the Au atoms and their surrounding C atoms. Further studies show that the magnetic properties still maintain under different doping concentrations (0.125-0.5 monolayer). Therefore, this study would provide great potential applications of diamond in novel magnetic semiconductors and transistors.

The electromagnetic field’s quantum nature and spin

The interaction of the electron (charge) with the electromagnetic field is investigated using the minimum coupling prescription, in which the electron’s spin appears in the Dirac and Pauli–Schrödinger equations. However, we analyze the use of this approach in Maxwell’s equations and the repercussions here. The application of this prescription resulted in novel electrodynamics associated with spin. The complex Maxwell’s equations are discovered to describe a massless electromagnetic field governed by the Dirac equation interacting with a particle with a double charge whose wavefunction is the electromagnetic field’s energy density. The conservation equation for electromagnetic field helicity (spin) is obtained directly from the new electrodynamics. We demonstrated that the quantization of the electromagnetic field (Maxwell’s equations) interacting with a photon field results in the electromagnetic field’s quantization. The energy density of the electromagnetic field is shown to fulfill a massless Dirac equation. This indicates the material nature of the electromagnetic field (photon). As a result, the electromagnetic spin charge and current densities are determined. We obtained the Josephson energy–current relationship from the spin current produced by an electromagnetic field. A quantum nonlinear Ohm’s law is developed. Quantum power and force associated with the quantum nature of the electromagnetic field are proposed.

Deconfined criticalities and dualities between chiral spin liquid, topological superconductor and charge density wave Chern insulator

We propose bi-critical and tri-critical theories between chiral spin liquid (CSL), topological superconductor (SC) and charge density wave (CDW) ordered Chern insulator with Chern number C=2C=2 on square, triangular and Kagome lattices. The three CDW order parameters form a manifold of S^2S2 or S^1S1 depending on whether there is easy-plane anisotropy. The skyrmion defect of the CDW order carries physical charge 2e2e and its condensation leads to a topological superconductor. The CDW-SC transitions are in the same universality classes as the celebrated deconfined quantum critical points (DQCP) between Neel order and valence bond solid order on square lattice. Both SC and CDW order can be accessed from the CSL phase through a continuous phase transition. At the CSL-SC transition, there is still CDW order fluctuations although CDW is absent in both sides. We propose three different theories for the CSL-SC transition (and CSL to easy-plane CDW transition): a U(1)U(1) theory with two bosons, a U(1)U(1) theory with two Dirac fermions, and an SU(2)SU(2) theory with two bosons. Our construction offers a derivation of the duality between these three theories as well as a promising physical realization. The SU(2)SU(2) theory offers a unified framework for a series of fixed points with explicit SO(5), O(4)SO(5),O(4) or SO(3)× O(2)SO(3)×O(2) symmetry. There is also a transparent duality transformation mapping SC order to easy-plane CDW order. The CSL-SC-CDW tri-critical points are invariant under this duality mapping and have an enlarged SO(5)SO(5) or O(4)O(4) symmetry. The DQCPs between CDW and SC inherit the enlarged symmetry, emergent anomaly, and self-duality from the tri-critical point. Our analysis unifies the well-studied DQCP between symmetry breaking phases into a larger framework where they are proximate to a topologically ordered phase. Experimentally the theory demonstrates the possibility of a rich phase diagram and criticality through closing the Mott gap of a quantum spin liquid with projective symmetry group.

Electronic band structures and spin-charge densities of edge-functionalized silicene nanoribbons as promising candidates for either optoelectronics or spintronics applications

Two-dimensional nanomaterials including graphene as well as its nanoribbons have started to occur, which has accelerated the growth of contemporary nanotechnology. Silicene, a silicon equivalent of graphene, has the main advantage that it can be employed in present silicon nanostructure-based production processes. Using density functional theory within the generalized gradient approximation, we offer the structural, electronic, and magnetic properties of edge-functionalized silicene nanoribbons (nX-zSiNR-mX’)(where, X/X’ = F, Cl or H; n, m = 1 or 2) in magnetic-order NM, FM, and AFM, respectively. Two modes homogeneous and heterogeneous asymmetric are accomplished. The spin density is mainly localized on halogen and Si atoms. Thus, future spin-dynamics processes for spintronics applications could be accomplished on these systems. Our computed outcomes reveal that the pristine nanoribbon 8-SiNR is a metal material once the NM and FM magnetic orders are involved, whereas it is a semiconductor with a small band gap energy when the AFM magnetic order is employed. Moreover, we find that the zigzag nX-zSiNR-mX’ compounds are metals in either case homogeneous or even heterogeneous. Nevertheless, a band gap energy up a limit to 520 meV (2H-zSiNR-1H) can be achieved under an external electric field with a strength of 4.0 V/Å. We carefully investigate the effect of the edge-functionalized silicene nanoribbon width on their spin density distribution and electronic band structures. Further, the effect of nanoribbon width on the edge formation energy and magnetic moment is systematically studied. Our outcomes reveal the potential of these nanoribbons as advantageous candidates for silicon photonic, optoelectronic devices, and spintronics applications.

High piezoelectric-magnetic coupling in potassium-sodium niobate piezoelectric ceramics prepared by solution synthesis

BiFeO3 is a multiferroic material that is difficult to synthesize by conventional solid-reaction methods. In this work, high piezoelectric-magnetic coupling was realized in a (1−x)(K0.5Na0.5)NbO3−xFe2O3 piezoelectric ceramic synthesized by combining solution synthesis and a conventional solid-reaction method. The remanent magnetization (Ms of ∼150 memu/g and Mr of ∼43 memu/g at 20 kOe) and remanent polarization (Pr of ∼8.12 μC/cm2) were achieved simultaneously for the 0.8KNN–0.2Fe2O3 ceramic, which were considerably higher than those of reported perovskite-type multiferroelectric ceramics and BiFeO3 obtained by the conventional solid-reaction method. This high piezoelectric-magnetic coupling was ascribed to the interplay of KNN and Fe2O3, which improved the magnetic performance by increasing the spin charge density and exchange-coupling-mediated electrically driven magnetization. Furthermore, the (1–x)(K0.5Na0.5)NbO3–xFe2O3 ceramics possessed higher piezoelectric constants (d33 = 80–115 pC/N) than KNN because appropriate Fe2O3 formed smaller domains even at the nanoscale, thereby enhancing Pr. Therefore, this study provides an alternative strategy for the synthesis of perovskite-type multiferroelectric ceramics with high piezoelectric-magnetic coupling to meet the increasing miniaturization and functional requirements of electronic components.

Structural, electronic, and magnetic properties of MnSi and Mn4Si7 nanowires

The importance of nanoscale magnetism under tailored phase evolution has been gaining considerable interest in the past few decades, attributable to the surging demand for memory devices and emerging electromagnetism. Herein, we present experimental demonstrations and theoretical studies on the structural, electronic, and magnetic properties of MnSi and Mn4Si7 nanowires grown by thermal chemical vapor deposition. The crystallinity of the nanowires was confirmed by a high-resolution transmission electron microscope and elemental distribution. The ratio of Mn to Si (∼0.96–1.04) indicates uniformity in MnSi composition. Additionally, the Mn4Si7 nanowire has an Mn/Si ratio of ∼0.78–0.87, which deviates from the homogenous Mn4Si7 ratio of ∼ 0.6 due to a higher Mn content at the nucleation sites. We found that the MnSi nanowires remained ferromagnetic (FM), similar to bulk MnSi, whereas the Mn4Si7 nanowires exhibited an FM order in contrast to the non-magnetic nature of bulk Mn4Si7. Field-cooled and zero-field-cooled magnetization curves reveal that the Mn4Si7 nanowires exhibited an FM order with a transition temperature (Tc) above room temperature. In contrast, the MnSi nanowires have a lower Tc of ∼ 30 K. It is noting that the First-principles density functional theory calculations demonstrated that both MnSi and Mn4Si7 nanowires possess a metallic characteristic. The spin-charge density of Mn4Si7 nanowires was found to be localized near the surface, implying a surface-induced magnetism. These findings suggest the possibility of tunning the phase evolution of Si-based nanowires by simply changing the diffusion mechanism of the Mn precursor. These metallic nanowires may be used as nanoscale interconnects and gate electrodes in nanoscale technologies.

Evolution of the Fe-Co magnetism and magnetic proximity effects in alternate Fe/Co monolayers on nonmagnetic Cu3Au(001)

Magnetic heterostructures with ferromagnetic/nonmagmetic interfaces are very interesting materials due to the possibility to switch the magnetization, to control the induced magnetic moment, and also due to interfacial effects. The tuning of the spin-orbit coupling in magnetic materials allows engineering new spintronic devices. Using density functional theory, the induced local magnetic moments in copper and gold surface atoms of ${\mathrm{Cu}}_{3}\mathrm{Au}(001)$ due to the deposited alternate magnetic Fe and Co monolayers were studied. To observe the tuning mechanism, the spin density of the $\mathrm{FeCo}/{\mathrm{Cu}}_{3}\mathrm{Au}(001)$ as a function of the number of deposited magnetic monolayers was extensively investigated. The Fe/Co deposition induces a hybridization between electronic states of the magnetic and nonmagnetic interface atoms, generating a broadening in $d$ bands of the deposited material, engineering the magnetic moments of the interface atoms. This observed hybridization elucidates the charge variation in the interface atoms for stacking sequences starting with Fe or with Co as the first magnetic layer in direct contact with the ${\mathrm{Cu}}_{3}\mathrm{Au}(001)$ substrate. By performing the spin-charge density calculations, we demonstrated that this magnetic induction occurs only for the nonmagnetic Cu-Au atoms at the ${\mathrm{Cu}}_{3}\mathrm{Au}(001)$ surface.

Investigation on magnetic properties of W-doped diamond via first-principles

The electronic and magnetic properties of W-doped diamond were investigated by first-principles calculation. The results revealed that the substitutional site was more favorable than interstitial site for W atom in diamond. The W-doped diamond exhibited the half metallic behavior and stable ferromagnetism with a magnetic moment of 2 μB, while the intrinsic diamond was non-magnetic. The density of states implied that magnetism originated from the p-d hybridization between the W-5d and C-2p states. The spin charge density and magnetic moment of W-doped diamond stemmed from the W atom and the surrounding C atoms. Therefore, the W-doped diamond would be a promising novel type of dilute magnetic semiconductor and could possess a great potential application in spintronic and micro-electromechanical system devices.

Moiré engineering of spin–orbit coupling in twisted platinum diselenide

We study the electronic structure and correlated phases of twisted bilayers of platinum diselenide using large-scale ab initio simulations combined with the functional renormalization group. PtSe2 is a group-X transition metal dichalcogenide, which hosts emergent flat bands at small twist angles in the twisted bilayer. Remarkably, we find that Moiré engineering can be used to tune the strength of Rashba spin–orbit interactions, altering the electronic behavior in a novel manner. We reveal that an effective triangular lattice with a twist-controlled ratio between kinetic and spin–orbit coupling (SOC) scales can be realized. Even dominant SOC can be accessed in this way and we discuss consequences for the interaction driven phase diagram, which features pronounced exotic superconducting and entangled spin-charge density waves.

Electronic and magnetic correlations in quantum entanglement of 1D Extended Hubbard Model

The Hubbard model is one of the basic models in condensed matter physics. It provides a simple way to understand how electron interactions can generate very rich phase diagrams. This paper aims to study its electronic, magnetic and quantum aspects. The considered Extended Hubbard Model (EHM) is parameterized by kinetic energy t, on-ste interaction energy U, off-ste interaction energy V and exchange spin–spin interaction J.The diagonalization of the t-U-V- model allows us to study the effect of V on some local properties of the half-filled chain fermions. The behaviour of ground state energy as a function of U and V shows that this model exhibits a conductor – insulator transition near the line U=2V. While, the diagonalization of the t-U-V-J- model shows that spin–spin interaction generates a Spin Density Wave (SDW) and Charge Density Wave (CDW) separation. Moreover, to study the quantum aspect of the t-U-V-J- model, we analyse the behaviour of its quantum entanglement. The obtained results show that the quantum entanglement reach its maximum value for an optimal inter-atomic distance.

Electronic and magnetic properties of LaRuO3 and LaFeO3: Orbital order and canted antiferromagnetism

The electronic and magnetic structures of LaRuO3 has been attracted much attention. The remaining problem is to identify and understand the ground-state of LaRuO3. To clarify the situation we chose the LaFeO3 as a comparison and evaluated the ground-state properties by first-principles calculations. We found the LaRuO3 was GdFeO3-type Jahn-Teller distorted for the longer Ru-O bonds. The electronic structure calculations identified the LaRuO3 was a G-type antiferromagnetic insulator. The low spin eg0t2g5 population and the RuO6 octahedron distortion induced the LaRuO3 orbital ordered which was found from the spin charge density. We also found the onsite Coulomb interactions U regulated the ground-state and the spin-orbital coupling persisted the orbital order. The simulations of magnetic properties suggested the LaRuO3 was canted antiferromagnetic ordered with a lower Neel temperature of 90 K compared to the 802 K of LaFeO3. The difference between LaFeO3 and LaRuO3 revealed that the 4d electrons in LaRuO3 introduced an orbital freedom.

DFT insights into the adsorption behavior of 4,6-dimethyldibenzothiophene on the Ni-Mo-S corner sites: Effect of the promoter magnetism

The computational method based on the first principle of numerical atomic functions of density functional theory (DFT) was established to investigate the effects of ferromagnetism for Ni species on the Ni-Mo-S monolayer nanocluster as well as the adsorption behavior of 4,6-DMDBT for the first time. The spin charge density analysis, the Hirshfield analysis, the frontier orbital analysis and the deformation charge analysis were performed. The results show that the ferromagnetism of Ni species significantly affected the spin charge density of the Ni-Mo-S corner active site, while it has little effect on the spin charge density of Ni-Mo-S edge sites due to the loss of magnetism caused by the frustrating interactions of the ferromagnetic Ni atom in the hexagonal honeycomb MoS2 structure. The 4,6-DMDBT adsorption behavior investigation results show that the ferromagnetism of the Ni species has greatly influenced the adsorption of 4,6-DMDBT over the magnetic corner active sites: type-2 adsorption configuration with adsorption energy of about 108.2 kJ·mol−1 is the predominant adsorption configuration without considering the magnetic features of Ni-Mo-S corner active site; while type-10 adsorption configuration with that of about 110.1 kJ·mol−1 becomes the predominant one after considering the magnetic features of Ni-Mo-S corner active site. The adsorption behavior of 4,6-DMDBT on the Ni-Mo-S edge active site has barely affected by the ferromagnetism of Ni Species. Besides, 4,6-DMDBT molecule is more inclined to adsorb on the corner active site via σ adsorption by formation of σ bond between the corner Ni atom and the S atom from 4,6-DMDBT.

Competition between spin density wave and charge density wave driven by interactions of spinful Haldane model on honeycomb lattices

We investigate the interacting spinful Haldane model with on-site and nearest-neighbor repulsions on honeycomb lattices. Interactions drive spin-density and charge-density waves competing with each other. This competition enriches the phase diagram of the system greatly, where both topological and non-topological coexistence phases emerge with spin-density and charge-density wave orders. Moreover, the topological phase transition accompanied by the energy gap closure in coexistence phases is of third order. Finally, we study the topological properties consisting of Chern numbers and edge states for different phases.

Band structure regulation in Fe-doped MgZnO by initial magnetic moments.

ZnO-based diluted magnetic semiconductors have high prospects in spintronics applications. In this study, the electronic and magnetic properties of Fe-doped MgZnO are studied by density functional theory calculations. The investigations of the band structure, total density of states, and projected density of states revealed a strong correlation between Mg and O atoms in addition to the magnetism and impurity level generated by the Fe atoms. In the spin charge density and band structure of 2.78% Fe-doped MgZnO, Fe atoms always cause paramagnetic coupling with oxygen atoms bonded around them, and when the initial magnetic moments were parallel, the band gap is broadened in the opposite channel. On the contrary, when the initial magnetic moments are anti-parallel, the band gap is narrowed in both the spin-up and spin-down channels. This shows that the initial magnetic moments have a great influence on the band structure, giving another way to tune the gap dynamically.

First-Principles Study of the New Half-Metallic Ferromagnetic Quaternary-Heusler Alloys NaXNO (X=Ca, Sr, Ba)

The first-principles approach based on density functional theory (DFT) and the full-potential linearized augmented plane-wave method were employed to investigate the structural, elastic, electronic and magnetic properties of Na[Formula: see text]NO ([Formula: see text], Sr and Ba) quaternary half-Heusler alloys. The generalized gradient approximation (GGA) as parameterized by Perdew, Burke and Ernzerhof (PBE) and the modified Becke–Johnson exchange potential were used. As far as we know, we present our results which for the first time quantitatively account for the electronic structures and magnetic properties of Na[Formula: see text]NO ([Formula: see text], Sr and Ba) quaternary half-Heusler alloys. From the total energy calculation using three possible atomic configurations ([Formula: see text], [Formula: see text] and [Formula: see text]), it is found that the Na[Formula: see text]NO ([Formula: see text], Sr and Ba) quaternary half-Heusler alloys are more stable in the ferromagnetic [Formula: see text]-phase. From our estimated elastic constants [Formula: see text], it is found that all the considered Heusler alloys are mechanically stable in the [Formula: see text]-phase. We have also investigated the robustness of the half-metallicity with respect to the variation of lattice constants in these alloys. We have found that these alloys are half-metallic ferromagnets (HMFs) with a magnetic moment of 2[Formula: see text][Formula: see text] per formula unit at their equilibrium volumes. The spin-polarized electronic band structure and density of states of these quaternary half-Heusler alloys calculated by GGA (mBJ-GGA) show that the minority spin channels have metallic nature and the majority spin channels have a semiconductor character with half-metallic gaps of 0.49[Formula: see text]eV (2.17[Formula: see text]eV), 0.72[Formula: see text]eV (2.28[Formula: see text]eV) and 0.96[Formula: see text]eV (2.22[Formula: see text]eV) for NaCaNO, NaSrNO and NaBaNO quaternary half-Heusler alloys, respectively. Analysis of the density of states and the spin charge density of these quaternary alloys indicates that their magnetic moments mainly originate from the strong spin-polarization of 2[Formula: see text] states of N atoms and O atoms.

DFT Investigation on the Electronic, Magnetic, Mechanical Properties and Strain Effects of the Quaternary Compound Cu2FeSnS4

The electronic, magnetic and mechanical properties of the quaternary compound Cu2FeSnS4 have been investigated with first principle calculations. Its half-metallicity has been identified with spin polarized band structures and its magnetic origination is caused by the strong spin splitting effect in the d orbitals of Fe atoms. The total magnetic moment of 4 μB is mainly contributed by the Fe atoms and the spatial distribution of the magnetic spin density and charge density difference have also been examined. Moreover, several mechanical properties of Cu2FeSnS4 have been derived and its mechanical stability is also verified. The directional dependent Young’s modulus exhibits relatively small anisotropy yet the shear modulus shows strong directional anisotropy. At last, the tetragonal strain effects have been evaluated and their impact on the electronic and magnetic properties are provided. Results show the total magnetic moment stays almost unchanged while the half-metallicity can only be maintained under relatively small variations for both strains. This study can provide comprehensive information about the various properties of Cu2FeSnS4 compound and serve as a helpful reference for its future applications.