Magnetic Atoms Research Articles

Electronic and Magnetic Properties of the Graphene/Y/Co(0001) Interfaces: Insights from the Density Functional Theory Analysis.

The effect of Y intercalation on the atomic, electronic, and magnetic properties of the graphene/Co(0001) interface is studied using state-of-the-art density functional theory calculations. Different structural models of the graphene/Y/Co(0001) interface are considered: (i) graphene/Y/Co(0001), (ii) graphene/1ML-YCo2/Co(0001), and (iii) graphene/bulk-like-YCo2(111). It is found that the interaction strength between graphene and the substrate is strongly affected by the presence of Y at the interface and the electronic structure of graphene (doping and the appearance of the energy gap) is defined by the Y concentration. For the Co-terminated interfaces between graphene and the metallic support in the considered systems, the electronic structure of graphene is strongly disturbed, leading to the absence of the linear dispersion for the graphene π band; in the case of the Y-terminated interfaces, a graphene layer is strongly n-doped, but the linear dispersion for this band is preserved. Our calculations show that the magnetic anisotropy for the magnetic atoms at the graphene/metal interface is strongly affected by the adsorption of a graphene layer, giving a possibility for one to engineer the magnetic properties of the graphene/ferromagnet systems.

In Situ Atomistic Insight into Magnetic Metal Diffusion across Bi0.5Sb1.5Te3 Quintuple Layers

AbstractDiffusion and occupancy of magnetic atoms in van der Waals (VDW) layered materials have significant impact on applications such as energy storage, thermoelectrics, catalysis, and topological phenomena. However, due to the weak VDW bonding, most research focus on in‐plane diffusion within the VDW gap, while out‐of‐plane diffusion has rarely been reported. Here, to investigate out‐of‐plane diffusion in VDW‐layered Bi2Te3‐based alloys, a Ni/Bi0.5Sb1.5Te3 heterointerface is synthesized by depositing magnetic Ni metal on a mechanically exfoliated Bi0.5Sb1.5Te3 (0001) substrate. Diffusion of Ni atoms across the Bi0.5Sb1.5Te3 quintuple layers is directly observed at elevated temperatures using spherical‐aberration‐corrected scanning transmission electron microscopy (STEM). Density functional theory calculations demonstrate that the diffusion energy barrier of Ni atoms is only 0.31–0.45 eV when they diffuse through Te3(Bi, Sb)3 octahedron chains. Atomic‐resolution in situ STEM reveals that the distortion of the Te3(Bi, Sb)3 octahedron, induced by the Ni occupancy, drives the formation of coherent NiM (M = Bi, Sb, Te) at the heterointerfaces. This work can lead to new strategies to design novel thermoelectric and topological materials by introducing magnetic dopants to VDW‐layered materials.

Electronic reconfiguration in layered Bi2SeO2 surface induced by dual-metal hybridization for hydrogen evolution reaction

The reaction activity of catalysts is strongly depended on the surface atomic reconfiguration and their electronic occupation. However, the relationship between surface electronic reconfiguration induced by dual-metal hybridization in layered Bi2SeO2 and their hydrogen evolution reaction (HER) still need to be understood. Comprehensive density functional theory (DFT) calculations disclose that the implanted magnetic Fe and Co atoms can rearrange the electronic occupation of Bi2SeO2 surface through orbital interaction and charge transfer, in which partial 6s lone pair electrons of the Bi3+cation is transferred into half-filled dopants. The electronic reconfiguration can disorder the spatial distribution of Bi3+ cation, leading to a higher HER activity and carrier transfer. This work provides a new insight into engineering surface atomic reconfiguration and catalytic activity.

Tuning the crystalline field leads to giant regulated perpendicular magnetic anisotropy by depositing Bi atom onto the MgO surface

Minimizing the size of magnetic units in miniaturized magnetic storage and spintronics inspires great interest to search for nanostructures with giant magnetic anisotropy energy (MAE). Here, we explore the possibility of perpendicular magnetic anisotropy (PMA) at atomic scale using a Bi atom deposited onto the MgO surface (Bi@MgO) by first-principles calculations. We find that Bi@MgO has high stability and large PMA with 204.76 meV. More importantly, the PMA can be effectively regulated by increasing the distance between Bi atom and the substrate, which reaches extremely large MAE of 314.68 meV at h = 2.6 Å. By analyzing the p-orbital-resolved MAE and the density of states of Bi atom, we find the large MAE mainly originates from the contributions of the quasi-degenerate p x/y near the Fermi level and the changing of MAE is mainly caused by the electronic states changing of 6p orbitals of Bi atoms because of the variation of crystal field . The fundamental study provides an idea to control MAE by tuning the crystal field around the magnetic atom. • The Bi atom deposited onto the MgO surface reaches the large PMA with 204.76 meV. • The PMA can be effectively regulated by tuning the crystalline field. • The PMA reaches extremely large MAE of 314.68 meV by regulating. • The large MAE mainly originates from the contributions of quasi-degenerate p x/y . • The changing of MAE is mainly caused by the electronic states changing of Bi atom.

Structure, magnetism, and electronic properties of MXene bilayer Fe2NO2Hx(x = 1.5, 1)/Ti2CO2 stacked heterojunction

In this study, the interface structures, atom-resolved magnetism, density of states (DOS), and spin polarization of atomic terminations in the MXene bilayer Fe2NO2Hx(x = 1.5, 1)/Ti2CO2 heterojunction were comprehensively investigated using first-principles calculations. The various interface relaxed atomic position behaviors of the atomic terminations were studied. Moreover, the atom-resolved spin magnetic moments of the magnetic atoms were changed due to the rehybridization caused by interface symmetry breaking. Further analysis on DOS and projected DOS indicated that the MXene bilayer Fe2NO2H/Ti2CO2 heterojunction interface preserved 100% spin polarization, indicating that the heterostructure has more advantages in spintronics applications.

Magnetocaloric, electronic, magnetic, optical and thermoelectric properties in antiferromagnetic semiconductor GdCrO3: Monte Carlo simulation and density functional theory

Density functional theory and Monte Carlo simulation are performed on the magnetocaloric, electronic, optical, thermoelectric and magnetic properties of GdCrO3. The density of states diagrams is discussed. The values of the exchange energy calculated between the magnetic configurations Gd and Cr atoms was calculated. The GdCrO3 has semiconductor character and antiferromagnetic behavior. The dielectric function, absorption and reflectivity are also investigated. The thermoelectric response is evaluated by calculating electrical conductivity, thermal conductivity and seebeck coefficient (S) by using BoltzTraP code. The magnetic moment of Cr and Gd are calculated. The Néel temperature has been obtained. The presence of spin reorientation transition is also observed in this system. The maximum magnetic entropy change and relative cooling power are found to be respectively, 2.64 J.K−1.kg−1 and 25 J.kg−1 for h = 5 T.

Magnetic exchange interaction in two-dimensional lattice under generalized Bloch condition

Two-dimensional magnetic material which has been rapidly developed in recent years, has potential applications in developing spintronic devices. In order to understand the magnetic properties of two-dimensional magnetic materials, it is necessary to comprehend the magnetic interaction which is estimated by the exchange parameters between the magnetic atoms. The calculation of the magnetic exchange parameters is based on the first-principle. The commonly used method of determining the values of exchange parameters is energy-mapping. However, this method has some disadvantages. In this paper, the spin-spiral dispersion relationship is derived under the Heisenberg interaction and the Dzyaloshinskii-Moriya (DM) interaction through the generalized Bloch condition of three common two-dimensional magnetic structures: a tetragonal structure, a hexagonal structure in which the cell contains one magnetic atom, a hexagonal structure in which the cell contains two magnetic atoms. The magnetic exchange parameters of some materials are calculated through the first principle. These materials are MnB, VSe <sub>2</sub> MnSTe and Cr <sub>2</sub>I <sub>3</sub>Cl <sub>3</sub>. Among them, the MnSTe and Cr <sub>2</sub>I <sub>3</sub>Cl <sub>3</sub> are two-dimensional Janus materials, which means that they have space-reversal symmetry broken, that is why there is DM interaction in the system.

Magnetic nanoribbons with embedded cobalt grown inside single-walled carbon nanotubes

Molecular magnetism and specifically magnetic molecules have recently gained plenty of attention as key elements for quantum technologies, information processing, and spintronics. Transition to the nanoscale and implementation of ordered structures with defined parameters is crucial for advanced applications. Single-walled carbon nanotubes (SWCNTs) provide natural one-dimensional confinement that can be implemented for encapsulation, nanosynthesis, and polymerization of molecules into nanoribbons. Recently, the formation of atomically precise graphene nanoribbons inside SWCNTs has been reported. However, there have been only a limited amount of approaches to form ordered magnetic structures inside the nanotube channels and the creation of magnetic nanoribbons is still lacking. In this work we synthesize and reveal the properties of cobalt-phthalocyanine based nanoribbons (CoPcNRs) encapsulated in SWCNTs. Raman spectroscopy, transmission electron microscopy, absorption spectroscopy, and density functional theory calculations allowed us to confirm the encapsulation and to reveal the specific fingerprints of CoPcNRs. The magnetic properties were studied by transverse magnetooptical Kerr effect measurements, which indicated a strong difference in comparison with the pristine unfilled SWCNTs due to the impact of Co incorporated atoms. We anticipate that this approach of polymerization of encapsulated magnetic molecules inside SWCNTs will result in a diverse class of protected low-dimensional ordered magnetic materials for various applications.

Tunning and Tailoring the Electronic and Magnetic Properties Via 3d-Transition Metal Atoms Adsorption in Mx2 (M=Hf, X= S, Se) Monolayer

Tunning and Tailoring the Electronic and Magnetic Properties Via 3d-Transition Metal Atoms Adsorption in Mx2 (M=Hf, X= S, Se) Monolayer

High‐Efficiency Power Generation Device of Magnetic Declination Thermoelectric Material and Multisource Coordination Optimization of Distribution Network

The first‐order phase transition compounds have attracted widespread attention from refrigeration enterprises and scientists due to their giant magnetocaloric effect and refrigeration temperature region spanning room temperature. Magnetic substances are crystal structures composed of magnetic ions or atoms with a certain thermal motion or vibration. This research mainly discusses the multisource coordination optimization of magnetic declination thermoelectric material efficient power generation device and distribution network. In this study, large doses of MnFe(P,Si) compounds with different ratios were prepared. The reason for choosing a large dose is that the properties and structures of the samples prepared in a large amount and a small amount will be more or less the same for the samples fired in the same proportion and in the same process. At the same time, mass production also prepares for future mass production. Thermomagnetic power generation described in this study is a form of power generation that converts thermal energy directly into electrical energy. The conversion of thermal energy to electric energy is realized by the change of magnetization in the closed coil by the thermomagnetic material in the magnetic field environment, and then, the change of the magnetic flux in the closed coil is realized. The distribution network refers to the power network that receives electrical energy from the transmission network or regional power plants and distributes it locally through distribution facilities or distributes it to various users step by step according to the voltage. It is composed of overhead lines, cables, towers, distribution transformers, isolating switches, reactive power compensators, and some ancillary facilities. A network that plays an important role in distributing electrical energy in the power grid. This research starts with the active distribution network scheduling priority and the distribution network scheduling coordination control framework. Combined with the scheduling and operation characteristics of each component in the distribution network, the coordinated optimization scheme of the distribution network and the source‐network load‐storage coordinated control framework are investigated and analyzed. The scheduling resources of the model include the power of the substation flowing into the distribution network, the output of the adjustable distributed power source, the output value of the energy storage element, the closing status of the tie switch, and the section switch. In the study, it was found that when the Fe content was 0.63, the Curie temperature of the compound could reach 273 K at the highest. Scientifically designing a thermomagnetic power generation demonstration device is an important part of the realization of thermomagnetic power generation. The magnetic declination thermoelectric materials designed in this study will help to improve the power generation efficiency.

Graphene Intercalation with Iron and Cobalt: a Brief Review

The attractiveness of graphene, a two-dimensional crystal consisting of carbon atoms arranged in a hexagonal lattice, for various technological applications stems from its outstanding physical, mechanical and optical properties. The intercalation of magnetic metal atoms under graphene is a flexible tool for creating new functional materials for electronics and spintronics. In this review, we consider the works devoted to the intercalation of graphene by iron and cobalt atoms, where graphene on a metal (graphene sythesized by chemical vapor deposition method) and dielectric (graphene grown on silicon carbide) substrate is used as the initial structure.

Magneto-electronic properties and manipulation effects of Fe-adsorbed Sb/WS<sub>2</sub> heterostructure

To study the induced magnetism mechanism and magneto-electronic properties of non-magnetic two-dimensional van der Waals heterostructure adsorbing magnetic atoms, we construct Sb/WS<sub>2</sub> heterostructure, and consider its adsorbed Fe atoms. The calculated adsorption energy shows that T<sub>W</sub>, V<sub>Sb</sub> adsorption are the most likely positions for Fe atom adsorbed below and above the heterostructure, respectively, and T<sub>S_M</sub> adsorption is the most likely position for Fe atom adsorbed between two monolayers. The induced magnetism is due to the electron-spin rearrangement caused by the expansion of valence electronic configuration (VEC) and charge transfer after Fe atoms have been adsorbed. The T<sub>W</sub> adsorption and the T<sub>S_M</sub> adsorption make the nonmagnetic semiconducting heterostructure become a half-semiconductor (HSC), while V<sub>Sb</sub> adsorption turns the heterostructure into a bipolar magnetic semiconductor (BMS). In particular, the calculated magnetized energy indicates that the interlayer T<sub>S_M</sub> adsorption leads the heterostructure to holding the highest magnetic stability, which is enough to resist the influence of thermal fluctuation at room temperature. Quantum manipulation can cause the heterostructure to produce abundant magnetism, especially the flexible change of magnetic phase. For example, the application of external electric field can give rise to the magnetic phase transition among HSC, HM (half-metal) and BMS for the heterostructure, and the vertical strain can make the heterostructure realize the magnetic phase transition among HSC, HM and MM (magnetic metal). This study shows that the heterostructure can increase the adsorption region of transition metal atoms (below, interlayer and above), so as to produce rich magnetism, especially for the interlayer adsorption of transition metals, its magnetic stability against temperature is significantly enhanced.

Topological properties of Sb(111) surface: A first-principles study

First-principles calculations based on the density functional theory were performed to systematically study the electronic properties of the thin film of antimony in (111) orientation. By considering the spin–orbit interaction, for stoichiometric surface, the topological states keep robust for six-bilayer case, and can be recovered in the three-bilayer film, which are guaranteed by time-reversal symmetry and inverse symmetry. For reduced surface doped by non-magnetic Bi or magnetic Mn atom, localized three-fold symmetric features can be identified. Moreover, band structures show that the non-trivial topological states stand for non-magnetic substitutional Bi atom, while can be eliminated by adsorbed or substitutional magnetic Mn atom.

Tuning the magnetic anisotropy of transition-metal atoms on two-dimensional In2Se3 substrate via ferroelectric polarization switching

Exploring large and tunable magnetic anisotropy (MA) in a single magnetic atom is of merit for information storage due to the highest information data density. In this work, we studied the MA of transition-metal atoms X (X = Co, Fe, Ir, Mo, Nb, Ta, Ti, V, W) adsorbed on the surface of two-dimensional (2D) ferroelectric (FE) In2Se3 by first-principles calculations. We find that when the ferroelectric polarization of the In2Se3 is switched, the strengths of the MA for Co, Ir, Nb and Ti single atoms can be changed, while the directions of the MA for Fe, Mo, Ta, V and W single atoms are reversed. Calculated electronic structure and orbital-resolved magnetic anisotropy energy suggest that the variations in the occupation of spin-minority state and the exchange splitting of d orbitals at Fermi level by switching FE polarization are responsible for the change of the strength and direction of the MA on X atoms.

Hilbert Space Shattering and Disorder-Free Localization in Polar Lattice Gases.

Emerging dynamical constraints resulting from intersite interactions severely limit particle mobility in polar lattice gases. Whereas in absence of disorder hard-core Hubbard models with only strong nearest-neighbor interactions present Hilbert space fragmentation but no many-body localization for typical states, the 1/r^{3} tail of the dipolar interaction results in Hilbert space shattering, as well as in a dramatically slowed down dynamics and eventual disorder-free localization. Our results show that the study of the intriguing interplay between disorder- and interaction-induced many-body localization is within reach of future experiments with magnetic atoms and polar molecules.

Spin valve effect in two-dimensional VSe[formula omitted] system

Vanadium based dichalcogenides, VSe2, are two-dimensional materials in which magnetic Vanadium atoms are arranged in a hexagonal lattice and are coupled ferromagnetically within the plane. However, adjacent atomic planes are coupled antiferromagnetically. This provides new and interesting opportunities for application in spintronics and data storage and processing technologies. A spin valve magnetoresistance may be achieved when magnetic moments of both atomic planes are driven to parallel alignment by an external magnetic field. The resistance change associated with the transition from antiparallel to parallel configuration is qualitatively similar to that observed in artificially layered metallic magnetic structures. Detailed electronic structure of VSe2 was obtained from DFT calculations. Then, the ballistic spin-valve magnetoresistance was determined within the Landauer formalism. In addition, we also analyze thermal and thermoelectric properties. Both phases of VSe2, denoted as H and T, are considered.

Band gap opening in the BiSbTeSe2 topological surface state induced by ferromagnetic surface reordering

Introducing magnetic exchange interaction into topological insulators is known to break the time-reversal symmetry and to open a gap at the Dirac point in the otherwise gapless topological surface states. This allows various novel topological quantum phenomena to be attained, including the quantum anomalous Hall effect and can lead to the emergence of the axion insulator phase. Among the different approaches, magnetic doping is an effective, but still experimentally challenging pathway to provide the magnetic exchange interaction. Here we demonstrate that epitaxial deposition of Co and Mn magnetic atoms onto the (0001) surface of the ${\mathrm{BiSbTeSe}}_{2}$ topological insulator with a coverage between 0.6 and 3 atoms per surface cell performed in a finely tuned temperature range of ${300}^{\ensuremath{\circ}}$--${330}^{\ensuremath{\circ}}\mathrm{C}$ leads to the substitution of pnictogen atoms in the surface layer with magnetic atoms and to the formation of a two-dimensional magnetic phase with out-of-plane magnetization as proved by SQUID magnetometry. This magnetic layer is responsible for the appearance of a gap in the Dirac surface state as revealed by laser-based microfocused angle-resolved photoelectron spectroscopy. Our measurements have shown that the gap exists within the temperature range of 15--100 K, where the out-of-plane magnetization persists. The presented experimental results are supported by relativistic ab initio calculations.

Singular magnetic dilution behavior in a quasicrystal approximant

We report the effect of magnetic dilution on the physical properties of $({\mathrm{Gd}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}){\mathrm{Cd}}_{6}$ approximant crystals (ACs), close siblings of their corresponding quasicrystal (QC). Compared to the pure system ${\mathrm{GdCd}}_{6}$, we observe remarkable changes in the thermodynamic and magnetic bulk properties near and below the static-ordering temperatures from diluting the magnetic Gd atoms with nonmagnetic Y atoms by only 1--3% $(x=0.01--0.03)$. On the other hand, the corresponding QC system exhibits a monotonic change in its spin-glass behavior upon the magnetic dilution. We discuss the origin of the magnetic-dilution behavior in the present AC system in terms of possible magnetic frustration and short-range magnetic correlation that can be linked to its peculiar structure.

Magnetic frustration in a van der Waals metal CeSiI

The realization of magnetic frustration in a metallic van der Waals (vdW) coupled material has been sought as a promising platform to explore novel phenomena both in bulk matter and in exfoliated devices. However, a suitable material platform has been lacking so far. Here, we demonstrate that CeSiI hosts itinerant electrons coexisting with exotic magnetism. In CeSiI, the magnetic cerium atoms form a triangular bilayer structure sandwiched by van der Waals stacked iodine layers. From resistivity and magnetometry measurements, we confirm the coexistence of itinerant electrons with magnetism with dominant antiferromagnetic exchange between the strongly Ising-like Ce moments below 7 K. Neutron diffraction directly confirms magnetic order with an incommensurate propagation vector k ~ (0.28, 0, 0.19) at 1.6 K, which points to the importance of further neighbor magnetic interactions in this system. The presence of a two-step magnetic-field-induced phase transition along c axis further suggests magnetic frustration in the ground state. Our findings provide a novel material platform hosting a coexistence of itinerant electron and frustrated magnetism in a vdW system, where exotic phenomena arising from rich interplay between spin, charge and lattice in low dimension can be explored.

Model studies of topological phase transitions in materials with two types of magnetic atoms

We study the topological phase transitions induced by Coulomb engineering in three triangular-lattice Hubbard models $AB_2$, $AC_3$ and $B_2C_3$, each of which consists of two types of magnetic atoms with opposite magnetic moments. The energy bands are calculated using the Schwinger boson method. We find that a topological phase transition can be triggered by the second-order (three-site) virtual processes between the two types of magnetic atoms, the strengths of which are controlled by the on-site Coulomb interaction $U$. This new class of topological phase transitions have been rarely studied and may be realized in a variety of real magnetic materials.