Magnetism and solid solution effects in NiAl (40% Al) alloys

The solid solution effects of ternary additions of transition elements in intermetallic Ni–40% Al were investigated by both experimental studies and theoretical calculations. Co solute atoms when sitting at Ni sublattice sites do not affect the lattice parameter and hardening behavior of Ni–40Al. On the other hand, Fe, Mn, and Cr solutes, which are mainly on Al sublattice sites, substantially expand the lattice parameter and produce an unusual solid solution softening effect. First-principles calculations predict that these solute atoms with large unfilled d-band electrons develop large magnetic moments and effectively expand the lattice parameter when occupying Al sublattice sites. The theoretical predictions were verified by both electron loss-energy spectroscopy (EELS) analyses and magnetic susceptibility measurements. The observed softening behavior can be explained quantitatively by the replacement of Ni anti-site defects (potent hardeners) by Fe, Mn, and Cr anti-site defects with smaller atom size mismatch between solute and Al atoms. This study has led to the identification of magnetic interaction as an important physical parameter affecting the solid solution hardening in intermetallic alloys containing transition elements.     

Olivine-Type MgMn0.5Zn0.5SiO4 Cathode for Mg-Batteries: Experimental Studies and First Principles Calculations

Magnesium driven reaction in olivine-type MgMn_0.5Zn_0.5SiO₄ structure is subject of study by experimental tests and density functional theory (DFT) calculations. The partial replacement of Mn in Oh sites by other divalent metal such as Zn to get MgMn_0.5Zn_0.5SiO₄ cathode is successfully developed by a simple sol–gel method. Its comparison with the well-known MgMnSiO₄ olivine-type structure with (Mg)_M1(Mn)_M2SiO₄ cations distribution serves as the basis of this study to understand the structure, and the magnesium extraction/insertion properties of novel olivine-type (Mg)_M1(Mn_0.5Zn_0.5)_M2SiO₄ composition. This work foresees to extend the study to others divalent elements in olivine-type (Mg)_M1(Mn_0.5M_0.5)_M2SiO₄ structure with M = Fe, Ca, Mg, and Ni by DFT calculations. The obtained results indicate that the energy density can be attuned between 520 and 440 W h kg⁻¹ based on two properties of atomic weight and redox chemistry. The presented results commit to open new paths toward development of cathodes materials for Mg batteries.     

Structural Parameters and Spin Filtering Properties of Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(<Emphasis Type="Bold">M</Emphasis>)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>P compound

In this work, we have explored the structural and magnetic properties of GaP-based diluted magnetic semiconductors (DMSs). Based on first-principle density functional theory (DFT) calculations and using a full potential linearized augmented plane wave (FP-LAPW) method in generalized gradient approximation (GGA), some significant structural and magnetic properties of Ga _1?x (M) _x P compound as DMS are investigated. In this compound, M is a transition element such as vanadium (V), manganese (Mn), cobalt (Co), and copper (Cu) with a concentration of X. We have calculated the structural parameters such as the equilibrium lattice constant and bulk modulus of the compound. Furthermore, the spin polarization and magnetic moments are studied. We have found that by increasing the atomic number of the transition element, the lattice constant reduces, except for that of Cu, and compressibility improved in comparison with GaP. Moreover, with X=25 %, the Ga_0.75(M)_0.25P compound becomes more stable by increasing the atomic number of the transition element M. The study of the electronic properties of the compound indicates that the main contribution in total density of states near Fermi level is related to the 3d orbitals of the transition elements and the highest magnetic moment is for Mn-doped GaP.     

Investigation of Electronic and Magnetic Properties of Iron(II)-Bromide Compound by First Principle,Mean Field,Series Expansion Calculations and Monte Carlo Simulation

The self-consistent abinitio calculations, based on DFT (density functional theory) approach and using FLAPW (full-potential linear augmented plane wave) method, are performed to investigate both electronic and magnetic properties of the FeBr ₂ compound. Polarized spin and spin-orbit coupling are included in calculations within the framework of the ferromagnetic state between two adjacent Fe atoms. Magnetic moments considered to lie along (001) axes are computed. The antiferromagnetic and ferromagnetic energies of FeBr ₂ are estimated. Obtained data from abinitio calculations are used as input for the high-temperature series expansion (HTSE) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Fe–Fe in FeBr ₂ are established by using the mean field theory. The critical temperature T _C(K) is obtained by HTSEs combined with the Padé approximant method. The critical exponent γ associated with the magnetic susceptibility is established. The critical temperature and magnetic hysteresis cycle are obtained by Monte Carlo simulation.     

First Principle Study of the Structural, Electronic and Magnetic Properties of MgO Nanolayers on Fe Substrate

We have investigated the structural, electronic, and magnetic properties of MgO nanolayers with two different nanolayer thicknesses (1.5 nm and 1.75 nm) on a Fe substrate. The calculated results in this paper were obtained using the density functional theory (DFT) within the generalized gradient approximation (GGA). The total energies as a function of volume are calculated and thereby the lattice parameters, bulk moduli of MgO nanolayers with two different thicknesses have been calculated. The effects of surface atoms and Fe substrate atoms on physical properties of these nanolayers have been analyzed using the calculated total and partial electron density of states in its ferromagnetic phase. The spin-polarized density of states of MgO shows that this compound is an insulator in the nonmagnetic phase. MgO nanolayers on Fe substrate are metal in the ferromagnetic phase. The magnetic properties of surface atoms and Fe substrate atoms have been investigated and compared with bulk. Furthermore, the effect of hydrostatic pressure on the total and local magnetic moment of these nanolayers has been investigated.     

Half-metallic Ferromagnetism in the Ti2FeGe Heusler Compound: A First-Principles Study

In this paper, the structural, electronic and magnetic properties of the Ti₂FeGe Heusler alloy with CuHg₂Ti-type structure have been investigated using first-principles calculations based on density functional theory (DFT). It was predicted that the Ti₂FeGe Heusler alloy is a half-metal with a magnetic moment of 2μ _B per formula unit for the equilibrium lattice parameter. The minority-spin and spin-flip gaps were calculated to be 0.84 and 0.34 eV, respectively. In addition, the band structure and density of states (DOS) were studied. The magnetic moments of Ti(1) and Ti(2) atoms are antiparallel to that of Fe atoms showing ferrimagnetic arrangement. It was noted that the half-metallicity exists within a wide range of the lattice constant (5.54–6.55 Å) which makes the Ti₂FeGe Heusler alloy an interesting material in the field of spintronics.     

Theoretical Study of Electronic and Magnetic Properties of Newly Derived Iron–Pnictide Compound

A theoretical study based on DFT-LDA of the structural, electronic, and magnetic properties of the new substitution CaFe₂B₂ compound derived from BaFe₂As₂ is presented. Through a relaxation calculation, we found that this compound crystallizes in tetragonal and orthorhombic phases. Formation energies, lattice parameters, density of states, and magnetic moments are calculated. The ground state for this compound is nonmagnetic (NM). As for the anti-ferromagnetic state, more formation energy is characterized by large magnetic moment on each Fe atoms for AFM spin configuration. The results are compared with previous calculations and experimental data. The results of electronic and magnetic properties show that the partial and total density of states for NM, FM, and AFM phases are characterized by strong hybridization between Fe and B atoms. The energy band structure indicates the presence of overlapping valence and conduction bands at the Fermi level. The analyses of charge densities show that the type of bonding in the CaFe₂B₂ compound is metallic. An important resemblance with the original compound is observed which leads us to think that this compound is maybe a superconducting material.     

Structural and Magnetic Properties of Transition Metal-Adsorbed MoS<Subscript>2</Subscript> Monolayer

The electronic and magnetic properties of transition metal (TM) atoms (TM = Co, Cu, Mn Fe, and Ni) adsorbed on a MoS₂ monolayer are investigated by density functional theory (DFT). Magnetism appears in the case of Co, Mn, and Fe. Among the three magnetic cases, the Co-adsorbed system has the most stable structure. Therefore, we further study the interaction in the two-Co-adsorbed system. Our results show that the interaction between the two Co atoms is always ferromagnetic (FM) and the p–d hybridization mechanism results in such ferromagnetic states. However, the FM interaction is obviously suppressed by increasing the Co–Co distance, which could be well explained by the Zener–Ruderman–Kittel–Kasuya–Yosida (RKKY) theory. Moreover, similar magnetic behavior is observed in the two-Mn-adsorbed system and a longrange FM state is shown. Such interesting phenomena suggest promising applications of TM-adsorbed MoS₂ monolayer in the future.     

Anharmonicity and electron-phonon coupling in cuprate superconductors studied by inelastic neutron scattering

An overview is given on anharmonic lattice vibrations originating from structural instabilities. The transverse vibrations of the chain oxygens in YBa₂Cu₃O₇ are found to be only moderately anharmonic. Measurements of the phonon linewidths in the Cu-O bond stretching vibrations strongly support recent calculations of the electron-phonon coupling. Results are presented on superconductivity-induced frequency shifts at short wavelengths.     

First-Principles Study of Pressure-Induced Structural and Magnetic Phase Transitions of Binary Ferromagnets: MnSn and MnSb

First-principles calculations within density functional theory have been performed to study the structural and magnetic phase transitions of two 3d compounds (MnSn and MnSb) under pressure. We consider the rocksalt (B1), cesium chloride (B2), zinc-blende (B3), nickel arsenide (B8₁) modifications of MnSn and MnSb. Both spin-polarized and nonspin-polarized calculations are carried out for ferromagnetic (FM) and paramagnetic (PM) states, which can be used to distinguish the ground-state magnetic configuration with increasing pressure. The crystal structure preferences and the possible phase transitions among them have been studied. We report FM B8₁?^14GPaFM B2?^145GPaPM B2 phase transition for MnSn, FM B8₁?^23GPaPM B2 for MnSb. Phonon band dispersions, density of phonon states, and elastic stiffness constants are given and used to analyze the lattice dynamical and mechanical stability for the pressure-induced phase. Electronic band structures and density of states at different pressures are given to discuss the detailed electronic and magnetic properties.     

Simple explanation for the reentrant magnetic phase transition in Pr<Subscript>0.5</Subscript>Sr<Subscript>0.41</Subscript>Ca<Subscript>0.09</Subscript>MnO<Subscript>3</Subscript> perovskite

The reentrant magnetic phase transition in Pr _0.5Sr_0.41Ca_0.09MnO₃ perovskite is explained using the Ising spin model on the square lattice with mixed ferromagnetic and antiferromagnetic exchange interactions. It is shown using numerical calculations that this effect is strongly affected by the external magnetic field and lattice disorder.     

Electronic and Magnetic Properties of MnSb Compounds

The self-consistent ab initio calculations, based on density functional theory (DFT) approach and using full-potential linear augmented plane wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the MnSb compounds. Polarized spin and spin-orbit coupling are included in calculations within the framework of the ferromagnetic state between two adjacent Mn atoms. The ferromagnetic energy of MnSb systems is obtained. Magnetic moment considered to lie along the (001) axes are computed. The exchange interactions between the magnetic atoms Mn–Mn in MnSb are given using the mean field theory. Obtained data from ab initio calculations are used as input for the high-temperature series expansions (HTSEs) calculations to compute other magnetic parameters. The HTSEs of the magnetic susceptibility of the magnetic moments in MnSb (m _Mn) is given up to the tenth order series in (x = J ₁(Mn–Mn)/ k _B T). The critical temperature T _C is deduced by HTSEs of the magnetic susceptibility series combined with the Padé approximation method. The critical exponent γ associated with the magnetic susceptibility is deduced as well.     

Structural and magnetic properties of LaFe0.5Cr0.5O3 studied by neutron diffraction, electron diffraction and magnetometry

The structural and magnetic properties of the perovskite type compound LaFe_0.5Cr_0.5O₃ have been studied by temperature dependent neutron powder diffraction and magnetization measurements. Rietveld refinement of the neutron diffraction data shows that the compound crystallizes in an orthorhombic perovskite structure with a random positioning of the Fe and Cr cations at the B sublattice. The magnetic structure at 10 K is a collinear antiferromagnetic one with the magnetic moment per site being equal to 2.79(4) μ_B. Magnetisation measurements confirm the overall antiferromagnetic behaviour. Moreover, it indicates a weak uncompensated magnetic moment close to the transition temperature T_N ≈ 265 K. This moment can be described by a magnetic cluster state, which remains up to 550 K. Electron diffraction patterns along with high-resolution transmission electron microscopy images reveal that the crystallites are composed by domains of different orientation, which share the same cubic perovskite sub-cell reflections.     

Crystal and magnetic study of the disordered perovskites Ca(Mn0.5Sb0.5)O3 and Ca(Fe0.5Sb0.5)O3

We have investigated the double perovskites Ca₂MSbO₆ (M = Mn, Fe) that have been prepared by solid-state reaction (M = Fe) and wet chemistry procedures (M = Mn). The crystal and magnetic structures have been studied from X-ray (XRD) and neutron powder diffraction (NPD) data. Rietveld refinements show that the crystal structures are orthorhombic (space group Pbnm) with complete disorder of M and Sb cations, so the formula should be rewritten as Ca(M_0.5Sb_0.5)O₃. Due to this disorder no evidences of Jahn-Teller distortion can be observed in the MnO₆ octahedra of Ca(Mn_0.5Sb_0.5)O₃, in contrast with the ordered double perovskite Sr₂MnSbO₆. Ca(Fe_0.5Sb_0.5)O₃ behaves as an antiferromagnet with an ordered magnetic moment for Fe³⁺ of 1.53(4)μ_B and a propagation vector k = 0, as investigated by low-temperature NPD. The antiferromagnetic ordering is a result of the high degree of Fe/Sb anti-site disorder of the sample, which originates the spontaneous formation of Fe-rich islands, characterized by the presence of strong Fe-O-Fe antiferromagnetic couplings with enough long-range coherence to produce a magnetic contribution perceptible by NPD. By contrast, the magnetic structure of Ca(Mn_0.5Sb_0.5)O₃ cannot be observed by low-temperature NPD because the magnitude of the ordered magnetic moments is below the detection threshold for neutrons.     

Bond-order potential for transition metal carbide cluster for the growth simulation of a single-walled carbon nanotube

A classical many-body potential for transition metal carbide cluster is developed in the form of the bond-order type potential function. The parameter sets between carbon atoms and several transition metal atoms (Fe, Co and Ni) are constructed by fitting binding energies from Density Functional Theory (DFT) calculations. Using the potential function, clustering process of carbon atoms to a small metal cluster is studied by classical molecular dynamics (MD) simulation. The number of hexagonal rings in the Co cluster increases about twice as fast as in the Fe cluster. This implies that the graphitic lattice interacts more strongly with Co atoms than with Fe atoms. A Co cluster has a crystal structure where metal atoms are regularly allocated and embedded in the hexagonal carbon network in the simulation. In contrast, carbon atoms cover the entire surface in case of the Fe cluster. Additionally, the potential energy surface that a carbon atom feels from a 2D closed-packed facet is examined using a hypothetical FCC(1 1 1) facet of several transition metals. The potential energy minima are distributed on the hexagonal network showing the 2D closed-packed facet can be a template where a graphene is formed.     

Microstructure and magnetic properties in Mn-doped Nd-Fe-B magnets

The effect of the addition of antiferromagnetic element Mn on the local structure and the magnetic properties of Nd₉Fe₈₅B₆ magnets has been studied. It was found that the microstructure and local structure heavily depended on both the Mn addition and the quenched speed. The Mn additions could promote the order degree around Fe atom in as-spun samples. After appropriate annealing, the completely crystallized samples were obtained. It showed that the difference of the local structures around Fe atoms almost disappeared and the hard magnetic properties, especially the coercivity was enhanced. It is presumed that the enhanced hard magnetic properties were attributed to the enhancement of the exchange coupling, which is between the hard phases and the soft phases.     

Structural,Electrical and Magnetic Behaviour of FeTe0.5Se0.5 Superconductor

We report the synthesis as well as structural and physical properties of the bulk polycrystalline FeTe and FeTe_0.5Se_0.5 compounds. These samples are synthesised by the solid state-reaction method via vacuum encapsulation. Both studied compounds are crystallized in a tetragonal phase with space group P4/nmm. The parent FeTe compound shows an anomaly in resistivity measurement at around 78 K, which is due to the structural change along with a magnetic phase transition. The superconductivity in the FeTe_0.5Se_0.5 sample at 13 K is confirmed by the resistivity measurements. DC magnetisation along with an isothermal (M–H) loop shows that FeTe_0.5Se_0.5 possesses bulk superconductivity. The upper critical field is estimated through resistivity ρ (T,H) measurements using Gingzburg–Landau (GL) theory and is above 50 T with 50 % resistivity drop criterion. The origin of the resistive transition broadening under magnetic field is investigated by thermally activated flux flow. The magnetic field dependence of the activation energy of the flux motion is discussed.     

Interactions between transition metals and defective carbon nanotubes

Interactions between 3d transition-metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) and (5,5) carbon nanotube (CNT) with a vacancy defect are quantitatively characterized using first-principles calculations. The binding energies between CNT and transition metals are found to be significantly enhanced when vacancy defects are introduced into the CNT. For the defective CNTs doped with Sc, Cr and Zn atoms, the structures of defective CNTs are found to be intact. The doping of Ti, Mn, Cu, Fe, Ni and Co alternates the structures of defective CNTs. Among all 3d transition metals, only the ferromagnetic metal atoms Fe, Co and Ni form bonds with carbon atoms of CNT, suggesting the important role of magnetic exchange interaction in the p–d hybridisation between carbons and transition-metal atoms. The results also indicate that the 3d transition-metal atoms acting as substitutional defects can substantially modify the electronic structure of CNT. It is suggested that these stable CNT-metal systems could become promising engineering materials in many fields such as CNT devices for various spintronics applications and CNT metal–matrix composites.     

Preparation of a new nanosized As2O3/Mn0.5Zn0.5Fe2O4 thermosensitive magnetoliposome and its antitumor effect on MDA_MB_231 cells

The purpose of our research is to explore the preparation method of a new nanosized As2O3/Mn0.5Zn0.5Fe2O4 thermosensitive magnetoliposome and study its antitumor effect on MDA_MB_231 cells. The liposomes prepared by the method of rotatory film and high-pressure homogenization were detected by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), nano-particles detector, atom fluorescence spectrophotometer and differential scanning calorimetry (DSC). The therapeutic effects of the nanosized thermosensitive magnetoliposomes combined hyperthermia on human MDA_MB_231 cells in vitro were evaluated by MTT assay and flow cytometry assay. The results indicated that the nanosized As2O3/Mn0.5Zn0.5Fe2O4 thermosensitive magnetoliposomes were prepared successfully. The liposomes were spherical, and most of them were single-room. The exat average diameter of them was 103.8 nm. EDS showed each nanosized As2O3/Mn0.5Zn0.5Fe2O4 thermosensitive magnetoliposome contained P, Mn, Zn, Fe, and As elements, and this proved liposomes have successfully entrapped As2O3 and Mn0.5Zn0.5Fe2O4. The encapsulation ratio of As2O3 detected by atom fluorescence spectrophotometer was 82.16%. The result of heating test showed that Mn0.5Zn0.5Fe2O4 can serve as a heating source upon alternating magnetic field (AMF) exposure leading the nanosized thermosensitive liposomes to reach its phase transition temperature (42.52 degrees C) and release As2O3. MTT assay and flow cytometry assay revealed that the therapeutic effect of the nanosized As2O3/Mn0.5Zn0.5Fe2O4 thermosensitive magnetoliposomes combined with hyperthermia upon AMF on MDA_MB_231 cells was much better than other groups.