Atomic Magnetic Moments Research Articles

Synthesis and spectroscopic studies of some transition metal complexes derived from bis-2-pyrazoline ligand

The present work focuses on the synthesis and spectroscopic studies of some metal complexes based on a novel bis-2-pyrazoline ligand; 5-(4-(1-carbamothioyl-5-(pyridin-3-yl)pyrazolidin-3-yl)phenyl)-3-(pyridin-3-yl)pyrazolidine-l-carbothioamide. This ligand was prepared via the cyclization reaction of 3-(4-((E)-3-oxo-3-(pyridin-3-yl)prop-1-en-1-yl)phenyl)-1-(pyridin-3-yl)prop-2-en-1-one with alkaline solution of thiosemicarbazide. The resulted 2-pyrazoline ligand was identified by the FT-IR, NMR and LC-MS spectroscopes, in addition to (C.H.N.S) elemental analyses. The complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) were prepared from their metal chlorides and ethanolic solution of the prepared ligand in 10% ammonia (mole ration 2:1 M:L). The octahedral geometry for all complexes was confirmed by atomic absorption, FT-IR, UV-Visible, magnetic moments and molar conductivity measurements. The thermal stability of the prepared complexes was confirmed by the thermal gravimetric analyses and the observed results indicated that the suggested chemical structure are in agreement with other data of elemental micro-analyses and flame atomic absorption spectroscopy.

Study on a stress-magnetic relationship of DO3 based on first principles

Based on the first principles, in this paper the stress-magnetic relationship model of the Fe3Si (DO3) phase in silicon steel was analyzed, and the band structure and electronic density states were calculated. The experimental results show that the atomic magnetic moment would increases with the increase of tensile stress, and decreases with the increase of compressive stress. The linear compressive strength of the DO3 crystal is stronger than the linear tensile strength, and this phenomenon could be explained by the band structure and electronic density states. In addition, the macro verification experiment is designed. The silicon steel plate is used as the verification experiment sample, the change of silicon steel magnetic properties during the tension and compression process is measured. The experimental results show that the magnetic properties of silicon steel show an increasing trend in the tension process and a decreasing trend in the compression process, which qualitatively proves the correctness of the first principle calculation results. The MFM measurement results confirm that the stress would affect the magnetic domain. The stress-magnetic relationship of DO3 would provide theoretical support for electromagnetic detection and reduction of residual stress in silicon steel.

Chemical Mesoscopics Notions in the Explanation of Polymeric Materials Modification Mechanism with Participation of Metal Carbon Mesocomposites

The paper is dedicated to the consideration of the chemical mesoscopics notions application for the explanation of polymeric materials modification mechanism by the metal carbon mesoscopic composites. The main peculiarities of these nanosized particles are following: a) the presence of unpaired electrons on the carbon cover; b) the structure of carbon cover consists from poly acetylene and carbine fragments; c) the atomic magnetic moment of inner metal is equaled to more than 1,3 μB. The metal carbon mesocomposites activity depends on the medium and conditions influence because of the possible changes of the phase coherency and quantization of negative charges.

Первопринципные расчеты магнитной анизотропии пленок Fe и Co, разделенных прослойкой немагнитных металлов

This paper presents the results of numerical calculations of the magnetic characteristics of Co and Fe monolayer films on Cu and Pt surfaces using the VASP software package. The values ​​of the difference between the total energies of the antiferromagnetic and ferromagnetic configurations are calculated depending on the convergence parameters and the thickness of the nonmagnetic material. The values ​​of the magnetic anisotropy and magnetic moment of atoms in the structures of Co / Cu / Co, Fe / Pt / Fe, Co / Pt / Co, Pt / Co / Cu / Co / Pt are determined depending on the orientation of the surface face. For the (110) and (111) faces, the phenomenon of reorientation in the Co / Cu / Co structure is confirmed, when the anisotropy of the cobalt films parallel to the surface plane is replaced by the perpendicular anisotropy due to the introduction of an ultrathin platinum film into the structure.

Mini Review: Some Peculiarities of Chemical Mesoscopics and This Scientific Trend Development Perspective

In present mini review the definition of new scientific trend “chemical mesoscopics”, which is based on the ideas of the mesoscopic physics (mesoscopics) and also more latest mesoscopic chemistry, is given. This new scientific trend includes quantum notions on mesoparticle reactivity in chemical reactions. In these cases the negative charges quants interactions (interference) are considered as well as the interactions of negative and positive charges (annihilation). The schemes of the chemical bonds formation at the reactions flowing into mesoscopic reactors are presented. The especial attention is devoted to the interactions of metal (Copper, Nickel) carbon mesoparticles with such oxidizers as Ammonium Polyphosphate and Aluminum Oxide. In these reactions it is observed the reduction of Phosphorus and Aluminum, the growth of mesocomposite metal atomic magnetic moment and the simultaneous increasing of spin quantity on the mesocomposite carbon shell. The introduction of “annihilation” notion explains the increasing of magnetic characteristics. The modification of polymeric materials (on example of epoxy resins) by metal carbon mesocomposites is considered. For the mesoparticle (nanostructures) reactivity estimation the proposals are done. These proposals are concluded in the using of Fractal Theory ideas (Kolmogorov – Avrami equations) together with energetic analogs of reactivity theory.

Ab initio calculations of magnetic anisotropy of Co and Fe films on Cu and Pt surfaces

In this work, the results of numerical first-principles calculations of the magnetic characteristics for Co and Fe monolayer films on Cu(100) and Pt(100) slabs by using the VASP software package are presented. The values of the difference in the total energy of antiferromagnetic and ferromagnetic configurations depending on the parameters of convergence and thickness of non-magnetic material are calculated. Favorable magnetic anisotropy energy and values of the magnetic moment of atoms in the Co/Cu/Co, Co/Pt/Co, and Pt/Co/Cu/Co/Pt structures are determined. The phenomenon of reorientation in the Co/Cu(100)/Co structure, when the in-plane anisotropy of the cobalt films changes to an out-of-plane anisotropy due to the incorporation of an ultrathin platinum film into the structure is confirmed.

The hydrogen-termination effect on the electronic, magnetic, and optical properties of the (001) surface of Heusler alloy ZCl3 (Z = Li, Na, and K)

• ZCl-term of ZCl 3 (Z = Li, Na, K) surfaces at Z and Cl rich conditions are stable. • Spin polarizations of Li-ClCl and K-KCl surfaces are increased due to +H effect. • The magnetic moments of Cl atoms in the surface are changed due to +H effect. • There is obvious α peak at about 2 eV only for Li-ClCl surface due to +H effect. The hydrogen-termination effect on the electronic, magnetic, and optical properties of the (001) surface of Heusler alloy ZCl 3 (Z = Li, Na, and K) are studied by first-principles method. The ZCl-term of ZCl 3 (Z = Li, Na, and K) surfaces at the Z-rich and Cl-rich boundary conditions are more stable. The spin polarizations of both ClCl-term of LiCl 3 alloy and KCl-term of KCl 3 alloy (001) surface are increased, but the spin polarizations of the rest four surfaces are decreased, due to the hydrogen-termination effect. The atomic magnetic moments of Cl atoms in the surface are obviously changed due to the hydrogen-termination effect. The peak value α P (ω) of absorption coefficient in the energy range of visible light for the LiCl 3 , NaCl 3 , and KCl 3 bulk alloys shows the red-shift feature, and there is an obvious peak at about 2 eV for the ClCl-term of LiCl 3 alloy (001) surface with the hydrogen-termination effect.

Effect of non-Heisenberg magnetic interactions on defects in ferromagnetic iron

Fundamental flaws in the Heisenberg Hamiltonian are highlighted in the context of its application to bcc Fe, including the particular issues arising when modeling lattice defects using spin dynamics. Exchange integrals are evaluated using the magnetic force theorem. The bilinear exchange coupling constants are calculated for all the interacting pairs of atomic magnetic moments in large simulation cells containing defects, enabling a direct mapping of the magnetic energy onto the Heisenberg Hamiltonian and revealing its limitations. We provide a simple procedure for extracting the Landau parameters from density-functional theory calculations to construct a Heisenberg-Landau Hamiltonian. We quantitatively show how the Landau terms correct the exchange-energy hypersurface, which is essential for the accurate evaluation of energies and migration barriers of defects.

Metal-carbon mesocomposites application possibilities as the medicine magnetic transport within an organism

The paper is dedicated to the consideration of the metal-carbon mesocomposites application possibilities for the medicine magnetic transport. This trend is determined by correspondent peculiarities of content and structure of mesoscopic composites. The main peculiarities of these nanosized particles are the following: a) the presence of unpaired electrons on the carbon shell; b) the structure of carbon shell from poly acetylene and carbine fragments; c) the atomic magnetic moment of inner metal is equaled to more than 1–3 μB. The creation of reactive mesoscopic materials with regulated magnetic characteristics which can find application as medicine magnetic transport within an organism is very topical. The present investigation has fundamental character. It’s based on the ideas concerning to the change of metal-carbon mesocomposites reactivity. The use is possible as metal-carbon mesocomposites both and they are modified analogously.

Magnetic exchange mechanism in 3d transition-metal-doped LiZnAs

First-principles calculations were performed to study the electronic structure and magnetic properties of Li(ZnTM)As (TM = Ti, V, Cr, Mn, Fe, Co, Ni). The results showed that V, Cr, Mn and Fe were the most promising magnetic dopants for LiZnAs based DMSs. The magnetism of the doping systems originated from p-d hybridization. Among all the TM atoms, the maximum atomic magnetic moment provided by Mn was 4.74 μB. The ferromagnetic ground states were achievable in Ti-, V- or Cr-doped LiZnAs, and Li(ZnCr)As had the strongest ferromagnetic stability. Whereas, Mn-, Fe-, Co- or Ni-doped LiZnAs was antiferromagntic stable. To stabilize the ferromagnetism efficiently by the double exchange mechanism, there had to be delocalized anti-bonding states occupied partially. The antiferromagnetic super-exchange dominated when the 3d shells of magnetic impurities were half-filled or more than half-filled.

Semiconducting and magnetic properties within B(1-x)VxAs alloys at x = 0 and x = 0.25: A DFT + U study

The physical (mechanical (structural and elastic), electronic and magnetic) properties of the zincblende BAs parent compound and its B0.75V0.25As alloy are analyzed by employing the FP-L/APW + lo method as implemented in WIEN2k code, where the XC potential is approached by the GGA approximation. The analysis of the structural properties in B0.75V0.25As system indicates its stability in ferromagnetic state, where its computed equilibrium lattice parameters (the lattice constant (a0), the bulk modulus (B0), and the first-pressure derivative (B’) of the bulk modulus) are given. The elastic moduli (C11, C12, and C44) and anisotropy factor for the cubic system are determined for these compounds in the purpose to confirm their mechanical stability. The electronic structure of B0.75V0.25As shows its complete semiconducting feature. The electronic density of states indicates that the uncompleted 3d-V orbitals broaden on the width of the exchange splitting energies (Δx(d) and Δx(pd)); accordingly, the effective potential of minority-spin electrons are more attracted comparing to the majority-spin electrons. The magnetic properties unveil that the value of total magnetic moment of B0.75V0.25As alloy is found in an integer number. Thus, the hybridization between 3d-V and 4p-As states pushes to reduce the atomic magnetic moment of V element from its free space charge value and to produce local magnetic moments on B and As nonmagnetic sites. Moreover, the s-d exchange constant of conduction band (N0α) and the p-d exchange constant of valence band (N0β) are evaluated in the reason to know contributions during the exchange splitting process.

Dynamical diffraction effects in STEM orbital angular momentum resolved electron energy-loss magnetic chiral dichroism

In this work we derive sum rules for orbital angular momentum(OAM) resolved electron magnetic chiral dichroism (EMCD) which enable the evaluation of the strength of spin and orbital components of the atomic magnetic moments in a crystalline sample. We also demonstrate through numerical simulations that these rules appear to be only slightly dependent from the dynamical diffraction of the electron beam in the sample, making possible their application without the need of additional dynamical diffraction calculations.

An Ab Initio Study of Li/Ni-doped NaxMeO2 Cathode Material for Na-Ion Batteries

The current state-of-the-art quantum mechanics methodologies were applied to derive information on the bulk and surface properties of the P2-type layered oxide Na0.85Li0.17Ni0.21Mn0.64O2 (NLNMO), a cathode material. The special quasi-random structure (SQS) approach was employed to identify the arrangement of Li, Ni, and Mn ions in a supercell containing 115 atoms. Both the cell parameters and atomic positions were determined from DFT-PBE+U calculations to highlight specific distortions induced by the dopants (Ni and Li). The analysis of atomic partial charges and atomic magnetic moments revealed that Li has a purely structural role, while Ni and Mn actively participate in both redox processes and electronic conduction. Using a new surface slab model, the interaction between the layered Na0.85Li0.17Ni0.21Mn0.64O2 (001) surface and the Na ions was examined to identify the most favorable adsorption sites and the possible paths for the migration of the Na ions on the electrode surface.

X-Ray Photoelectron Study of the Formation of the Chemical Bond and the Atomic Magnetic Moment in Nickel-Carbon Nanocomposites Modified by d-Metal Oxides

X-ray photoelectron spectroscopy is used to study the modification of Ni/C nickel-carbon nanocomposites with oxides (NiO, CuO, and Fe2O3) in the ratio of 0.5–1.0. Depending on the type of modifier used and its content, the magnetic moment of Ni atoms changes in the nanocomposite, i.e., during the redox process, the nanocomposite structure changes and the interaction between the carbon skeleton and the modifier metal is enhanced. In the presence of electron acceptors, the paired d electrons of the nanocomposite metal become unpaired and move to higher orbitals. This is indicative of self-organization processes in nanostructures, which leads to an increase in the atomic magnetic moment of the metal.

Atomic, electronic and magnetic structure of an oxygen interstitial in neutron-irradiated Al2O3 single crystals

A single radiation-induced superoxide ion O_{2}^{ - } has been observed for the first time in metal oxides. This structural defect has been revealed in fast-neutron-irradiated (6.9×1018n/cm2) corundum (α-Al2O3) single crystals using the EPR method. Based on the angular dependence of the EPR lines at the magnetic field rotation in different planes and the determined g tensor components, it is shown that this hole-type O_{2}^{ - } center (i) incorporates one regular and one interstitial oxygen atoms being stabilized by a trapped hole (S = 1/2), (ii) occupies one oxygen site in the (0001) plane being oriented along the a axis, and (iii) does not contain any other imperfection/defect in its immediate vicinity. The thermal stepwise annealing (observed via the EPR signal and corresponding optical absorption bands) of the O_{2}^{ - } centers, caused by their destruction with release of a mobile ion (tentatively the oxygen ion with the formal charge −1), occurs at 500–750 K, simultaneously with the partial decay of single F-type centers (mostly with the EPR-active F+ centers). The obtained experimental results are in line with the superoxide defect configurations obtained via density functional theory (DFT) calculations employing the hybrid B3PW exchange-correlation functional. In particular, the DFT calculations confirm the O_{2}^{ - } center spin S = 1/2, its orientation along the a axis. The O_{2}^{ - } center is characterized by a short O–O bond length of 1.34 Å and different atomic charges and magnetic moments of the two oxygens. We emphasize the important role of atomic charges and magnetic moments analysis in order to identify the ground state configuration.

Electronic Structure and Magnetic Properties of the (111), (110), and (001) Surfaces for the Full Heusler Alloy Zr2VGa

In this paper, the electronic and magnetic properties of the Zr2VGa (111), (001), and (110) surfaces are studied via the first-principles calculations based on the density-functional theory. The calculations indicate that the Zr2VGa full-Heusler alloy displays a half-metallic behavior with a total spin magnetic moment of 2.0 μB at the equilibrium lattice parameter of 6.657 Ǻ. The energy band gap is 0.28 eV at the Fermi level. A weak relaxation at the terminations of the (111) and (001) surfaces is obtained which means that the terminations are stable. However, the stronger relaxations are at the terminations of the (110) surface. Examining the electronic density of states, the half-metallicity is determined which was verified in the bulk Zr2VGa and it is destroyed at the (111), (001) and (110) surfaces. Furthermore, it is discovered that the atomic spin magnetic moments at the Zr(2)Ga-terminated (001) surface is decreased compared to those of the bulk Zr2VGa, while the magnetic moments are increased at the Zr(1) and V-terminated (111) surfaces.

Magnetic behavior of transition metal solutes in [formula omitted]-iron: A classification

For several transition metals M, we have computed atomic magnetic moments for the body-centered cubic substitutional solid solution Fe1-xMx, by two comparative first-principle approaches for atomic disorder: Korringa-Kohn-Rostoker Coherent Potential Approximation (KKR-CPA) and Density Functional Theory applied to Special Quasirandom Structures (SQS-DFT). Our results, compared with experimental and numerical literature, led to a classification of transition metal solutes in α-iron with respect to their magnetic behavior.

Role of Fe addition in Ni–Mn–Ga–Co–Cu–Fe ferromagnetic shape memory alloys for high-temperature magnetic actuation

The Ni–Mn–Ga ferromagnetic shape memory alloys (FSMAs) are a group of active materials that undergo martensitic transformations (MTs) induced by temperature, stress and/or magnetic fields, resulting in large recoverable mechanical deformations. Their fast response and high energy density make them ideal candidates for implementation in sensors and actuators. Recently, the development of high-temperature FSMAs (HTFSMAs), working at temperatures over 373 K, has become an important task to meet the current requirements of modern technologies. The magnetic and magnetoelastic properties of FSMAs are very sensitive to the interactions between the magnetic moments of atoms that, in turn, depend on the atomic positions within the lattice. Here we investigate a series of the polycrystalline Ni45Mn25-xGa20Co5Cu5Fex (x = 0, 1, 2 and 5 at%) HTFSMAs. Their MT and Curie temperatures, the crystal structures of the martensitic and austenitic phases, the temperature evolutions of the lattice parameters of both phases and the atomic site occupancies have been studied by means of powder neutron diffraction measurements, complemented by standard characterization techniques. Based on the atomic site occupancies and additional measurements of the saturation magnetization, the influence of the structure and atomic ordering on the magnetism in these materials is analysed. The most promising candidate for high temperature magnetic actuation is the alloy with Fe 5 at%, following a combination of the high MT and Curie temperatures, around 370 K and 440 K, respectively, with a low tetragonality ratio, c/a ≈ 1.16, in the proximity of MT.

Layer-dependence of macroscopic and atomic magnetic correlations in Co/Pd multilayers

The development of multilayered materials with engineered magnetic properties compels a deep knowledge of physical properties at the atomic scale. The magnetic anisotropy is a key property in these materials. This work accounts for the magnetic anisotropy energy and its correlation with atomic properties of Co/Pd multilayers with the number of Co/Pd repetitions. Magnetometry measurements confirm stronger perpendicular magnetic anisotropy energies as the number of repetitions increases up to 40. However, the intrinsic anisotropy, related to the Co–Pd orbital hybridization and spin–orbit coupling, saturates at 15 repetitions. This finding is supported by x-ray magnetic circular dichroism analysis that reveals a direct correlation of the atomic Co and Pd orbital magnetic moments and the effective anisotropy of the system. The proximity effect that accounts for the Pd induced magnetization, along with the increasing Co moment, provides a suitable mechanism for the observed anisotropy energy layer dependence.

Material informatics for layered high-T C superconductors

Superconductors were typically discovered by trial-and-error aided by the knowledge and intuition of individual researchers. In this work, using materials informatics aided by machine learning (ML), we build an ML model of superconductors, which is based on several material descriptors with apparent physical meanings to efficiently predict critical superconducting temperature TC. The descriptors include the average atomic mass of a compound, the average number of electrons in an unfilled shell, the average ground state atomic magnetic moments, the maximum difference of electronegativity, etc. To fully optimize the ML model, we develop a multi-step learning and multi-algorithm cross-verification approach. For known high TC superconductors, our ML model predicts excellent TC values with over 92% confidence. When the ML model is applied to about 2500 layered materials in the inorganic crystal structure database, 25 of them are predicted to be superconductors not known before, including 12 cuprates, 7 iron-based crystals, and 6 others, with TC ranging from ∼32 K to ∼138 K. The findings shed considerable light on the mapping between the material descriptors and TC for layered superconductors. The ML calculates that in our descriptors, the maximum difference of electronegativity is the most important one.