Modulation of magnetic properties of bilayer SnSe with transition-metals doping in the interlayer

We investigate the spin-polarized electronic and magnetic properties of bilayer SnSe with transition-metal (TM) atoms doped in the interlayer by using a first-principles method. It shows that Ni dopant cannot induce the magnetism in the doped SnSe sheet, while the ground state of V, Cr, Mn, Fe and Co doped systems are magnetic and the magnetic moment mainly originates from 3d TM atom. Two types of factors, which reduce the magnetic moment of TM atoms doped in bilayer SnSe, are identified as spin-up channel of the 3d orbital loses electrons to SnSe sheet and spin-down channel of the 3d orbital gains electrons from 4s orbital. The spin polarization is found to be 100% at Fermi level for the Mn and Co atoms doped system, while the Ni-doped system is still a semiconductor with a gap of 0.26 eV. These results are potentially useful for development of spintronic devices.     

Features of Electronic Structure of Intermetallic Compounds CeNi<Subscript>4</Subscript>M (M = Fe,Co, Ni,Cu)

The evolution of the electronic structure of CeNi₄M (M = Fe, Co, Ni, Cu) intermetallics depending on the type of nickel substitutional impurity is explored. We have calculated band structures of these compounds and considered options of substituting one atom in nickel 3d sublattice in both types of crystallographic positions: 2c and 3g. The analysis of total energy self-consistent calculations has shown that positions of 2c type are more energetically advantageous for single iron and cobalt impurities, whereas a position of 3g type is better for a copper impurity. The Cu substitutional impurity does not change either the nonmagnetic state of ions or the total density at the Fermi level states. Fe and Co impurities, on the contrary, due to their considerable magnetic moments, induce magnetization of 3d states of nickel and cause significant changes in the electronic state density at the Fermi level.     

Quasiparticle band structure and optical spectrum of LiBr

The electronic structures of the Fe-doped perovskite ruthenates BaRu_1?x Fe _x O₃ with x = 0, 0.25, 0.5, 0.625, 0.75, and 1 are investigated through density-functional calculations. Large exchange splitting and small crystal field splitting are found in BaFeO₃, and a contrary scenario can take place on BaRuO₃ as expected since the Ru atom has a highly extended 4d orbital. The small exchange splitting and extended 4d states are the reasons why the obtained spin magnetic moment (0.628μ _B ) is significantly lower than the spin only value (2μ _B ) for the t _2g 3↑ t _2g 1↓ electronic configuration for Ru⁴⁺ ion. Further investigations suggest that Fe substitution at the Ru sites can suppress the bandwidths of Ru 4d orbital, leading to the half-metallic behaviour in BaRu_1?x Fe _x O₃ with x = 0.625 and 0.75. The different orbital feature of the Ru⁴⁺ ions in BaRu_0.375Fe_0.625O₃ is presented, which reflects the influence of Fe dopant on Ru 4d orbitals.     

Effects of copper(II) and iron(II) doping on the bound electronic states in the “one-dimensional” semiconductor Magnus' green salt

EPR and conductivity measurements on the “one-dimensional” semiconductor Magnus' Green Salt doped with Fe or Cu impurities are described. It is found that the introduction of these impurities causes significantly higher localization of the previously identified d_z2 holes.     

Study of the properties of some II–VI luminophors by Mössbauer spectrometry

Mössbauer spectrometric experiments on Fe⁵⁷ impurities embedded in synthetic ZnS (blende and wurtzite) and ZnO crystals were performed. The observed chemical isomer shifts are typical of Fe ions in configurations 3d⁶4s^x, with x ≈ 0.5 in ZnS; accidental d⁵ ions appear only at the beginning of the diffusion; alkaline cations cannot stabilize Fe ions in the d⁵ configuration; combined with the results of other authors, these shifts give a classification of the bond ionicities. The small broadening of the absorption lines in ZnS wurtzite allow us to evaluate the crystal field trigonal component as being very small; the positions and values of some nuclear quadrupole splitting doublets show that, depending on the preparation, S vacancies or substitutional oxygen atoms are always present and associated with a certain amount of impurities in such a way that their electronic energy levels are greatly perturbed. Similar associations of these defects with Dy³⁺ ions explain some variations of the fluorescence spectra of ZnS?Dy³⁺.     

Ferromagnetism in epitaxial germanium and silicon layers supersaturated with managanese and iron impurities

The possibility of laser synthesis of diluted magnetic semiconductors based on germanium and silicon doped with manganese or iron up to 10–15 at % has been shown. According to data on the electronic levels of 3d atoms in semiconductors, Mn and Fe impurities are most preferable for realizing ferromagnetism in Ge and Si through the Ruderman-Kittel-Kasuya-Yosida mechanism. Epitaxial Ge and Si layers 50–110 nm in thickness were grown on gallium arsenide or sapphire single crystal substrates heated to 200–480°C. The content of a 3d impurity has been measured by x-ray spectroscopy. The ferromagnetism of layers and high magnetic and acceptor activities of Mn in Ge, as well as of Mn and Fe in Si, are manifested in the observation of the Kerr effect, anomalous Hall effect, high hole conductivity, and anisotropic ferromagnetic resonance at 77–500 K. According to the ferromagnetic resonance data, the Curie point of Ge:Mn and Si:Mn on a GaAs substrate and of Si:Fe on an Al₂O₃ substrate is no lower than 420, 500, and 77 K, respectively.     

Volume and charging effects in alloy isomer shifts

Mössbauer isomer shift trends with d-atom impurities, ⁵⁷Fe in particular, in d-band hosts appear consistent with elementary ideas of volume and charge transfer. A rudimentary treatment based upon OPW-pseudopotential concepts is given.     

Correlation effects in the photoelectron spectra of 3d metals

An approximate method is presented for calculation of the orbital relaxation in photoelectron spectra for systems with a continuous distribution of electron states. The results for Fe, Ni and Cu 3d states explain the discrepancy between experimental data and band structure calculations. The nature of the satellite in photoelectron spectra of Ni is discussed.     

Electrotransport d'impuretes dans Cu et Ni

The effective valency of ⁵⁹Fe, ⁵⁸Co and ¹²⁵Sb in Cu and ⁵⁹Fe, ¹²⁵Sb in Ni has been determined using the thin-layer technique. The impurities are observed to move to the cathode in Ni, showing that the scattering of the holes of the d band dominates s scattering in Ni. In the Cu matrix, the resistivities obtained at the saddle point are rather small. A tentative explanation is given in terms of a virtual bound level on the impurity.     

Quantum chemical study of sulfur and hydrogen at the Σ=5 BCC Fe grain boundary

We investigate the effect of segregated atoms on metal-metal bonding at a grain boundary (GB). The structure and electronic properties of S and H impurities in Fe Σ=5 (013) [100] symmetrical tilt GB are studied using the atom superposition and electron delocalization molecular orbital (ASED-MO) theory. A large cluster containing 196 Fe atoms is used to simulate the local environment of the boundary. The results show that impurities induce large relaxation in the GB and that the GB gives rise to an energetically favorable zone for the H and S accumulation. No S-H association is found and the deleterious effect of H is of much less important as compared with S.     

Theory of E.P.R. of 3d impurities in metals

The application to the E.P.R. behaviour of dilute alloys of the generalized s-d interaction model appropriate to a 3d impurity with orbital degrees of freedom is considered. It gives rise in some cases to a large spin-lattice relaxation rate in addition to the usual cross relaxation to the conduction-electron spin. Our calculation shows why bottlenecking is effective for some 3d impurities and ineffective for others, leading to qualitative differences in the observed E.P.R. behaviour. It is emphasized that, as a result of the bottlenecking phenomenon, E.P.R. is a uniquely powerful method for determining the electronic states of 3d impurities in metals.     

X-ray magnetic circular dichroism at IrL2,3 edges in Fe100−x Ir x and Co100−x Ir x alloys: Magnetism of 5d electronic states

The formation of induced 5d magnetic moment on Ir in Fe_100−x Ir _x (x=3, 10 and 17) and Co_100−x Ir _x (x=5, 17, 25 and 32) alloys has been investigated by X-ray magnetic circular dichroism (XMCD) at Ir L_2,3 absorption edges. Sum rule analysis of the XMCD data show that the orbital moment of Ir is in the range of −0.071(2)μB to −0.030(1)μB in Fe-Ir alloys and −0.067(2)μB to 0.024(1)μB in Co-Ir alloys. We find that the total moment of Ir in Fe-Ir alloys is approximately 1/5 of the total 3d moment on Fe at all the three compositions. In contrast, the total moment on Ir in Co-Ir alloys varies between 1/6 to 1/16 of the 3d moment on cobalt. The observed trends of Ir moments and the role of interatomic exchange interactions in 5d moment formation are discussed.     

The influence of 3d transition metal substitution on the magnetic properties of MnGaGe

A study has been made of the effect of 3d transition element substitution on the magnetic moment and Curie temperature of MnGaGe. Substitution of 3d elements with atomic number less than Mn (i.e. Ti, V, or Cr) cause relatively small changes in magnetic properties, whereas substitution of Fe, Co, Ni and Cu cause a large reduction in moment and Curie temperature, e.g. substitution of 5 at.% Fe for Mn causes the moment to decrease by 30 per cent. The moment and ferromagnetism of MnGaGe are described in terms of a band model involving both strongly correlated and intinerant 3d electrons. The effect of 3d element substitution may be qualitatively understood in terms of this model.     

Reactivity and magnetism of Fe/InAs(100) interfaces

Interface reaction and magnetism of epitaxially-grown Fe on InAs(100) are studied by core-level photoemission (As 3d and In 4d) and Fe 2p X-ray magnetic circular dichroism using synchrotron radiation. The reactivity of Fe/InAs(100) is relatively low compared to that of other interfaces involving deposition of 3d metals on III-V semiconductors. As a consequence, we observe a magnetic signal at Fe L_{2, 3} edges for the lowest thicknesses studied (1 ML). The atomic magnetic moment reaches a value close to that of the bulk α-Fe (2.2 μ _B) for Fe coverages exceeding 5 ML. A ferromagnetic compound with approximate stoichiometry of FeAs is formed at the interface. The orbital magnetism represents between 12 and 20% of the total momentum, due to 3d density of states depletion and to crystal-field modification of the electronic levels. These properties make the Fe/InAs(100) interface very promising for spin-tunneling devices. Received 4 April 2002 / Received in final form 13 May 2002 Published online 31 July 2002     

On the electrical resistivity of noble based transition metal dilute alloys

We apply the CPA expression of the electrical conductivity to the case of Au-based alloys containing 3d and 4d transition impurities. In this approach, a s-diagonal disorder larger for the 3d case than for the 4d one can explain the measured differences in resistivity between these two cases.     

Variation of hyperfine splitting constants for 3d5-ions with interatomic distance

The hyperfine splitting constants A in the EPR spectra of the d⁵-ions of ⁵⁵Mn and ⁵⁷Fe as impurities in crystals increase with the size of the host ion and seem to approach an upper limiting value. Also, for divalent manganese in noncubic sites larger splittings along the directions of bond elongation are observed. Both effects can for ⁵⁵Mn be represented by a linear increase of about 0.1–0.2·10^?4 cm^?1 ppm. For ⁵⁷Fe the increase relative to the free ion value is about four times as large. An explanation for this variation with bond distance based on accompanying changes of covalency is proposed.The size of A can be used to decide which one of several possible sites is actually occupied by the transition metal ion. Other potential applications for the solution of structural details in amorphous or crystalline systems are indicated.     

The effect of Fe and Ru substitution on the superconductivity in MgCNi3

We report the effects of partial substitutions of the VIIIa elements: Fe (3d) and Ru (4d) in the intermetallic perovskite superconductor MgCNi₃. In both the MgCNi_3−xRu_x and MgCNi_3−xFe_x systems, the superconducting critical temperature (T_C) decreases monotonically as x is increased. T_C decreases more slowly in the case of Ru, suggesting that the 3d electrons in Fe are magnetically pair breaking. This is supported by the normal state magnetic susceptibility measurements (χ), which shows that χ increases with Fe and decreases with Ru doping. No ferromagnetism is observed in either system.     

Electronic structure of TiH2

The electronic structure of TiH₂ has been studied using the augmented-plane-wave method and the LCAO interpolation. The density of states and its orbital components show that the conduction band is Ti d-like and that the valence band is largely derived from the hydrogen orbitals with small Ti 3d hybridization. The electronic charges on the hydrogen atom are ～ 1.5 as compared to 1.6–1.7 of the rare-earth metal hydrides.     

Application of LAPW and Green-function methods to calculation of electronic structure of crystal defects

Calculations based on the Linear Augmented Plane-Wave (LAPW) which was treated by the KKR-Green-function method were performed for the electronic structure of 3d impurities (Sc, Ti, V, Cr, Mn, Fe, Co, Ni) in Cu-matrix as well as for vacancies in Cu and Ni. The results are in good agreement with experiments.