Inelastic magnetic X-ray scattering from highly correlated electron systems: La1.2Sr1.8Mn2O7, La0.7Sr0.3MnO3 and Fe3O4

Magnetic Compton profiles have been measured for the colossal magnetoresistance manganites La_1.2Sr_1.8Mn₂O₇ and La_0.7Sr_0.3MnO₃, and for magnetite Fe₃O₄, along various crystallographic directions, over a wide range of temperatures and magnetic fields. The experimental results are interpreted via first-principles computations for the double layer manganite, La_1.2Sr_1.8Mn₂O₇, and by using a simple model involving atomic d-orbitals and free electrons for the other two compounds. For all three materials a preference for the occupation of e_g orbitals is found, particularly, for orbitals of dx²−y² symmetry. An itinerant electron contribution is adduced at all temperatures in magnetite; such a contribution also appears in La_1.2Sr_1.8Mn₂O₇, but it is present only at low temperatures in La_0.7Sr_0.3MnO₃.     

Electron spin resonance in the Heusler alloy YbRh2Pb

An electron spin resonance (ESR) signal was observed in a concentrated Kondo lattice, Heusler alloy YbRh₂Pb. It is attributed to the combined effect of the 4f local magnetic moments of Yb³⁺ and conduction electrons. It is shown that the significant broadening and disappearance of the ESR line at temperatures above 20 K is caused by the processes of the spin-lattice relaxation of the Yb³⁺ ions through the first excited Stark doublet with an activation energy Δ ≈ 73.5 K. A comparison of the ESR data for YbRh₂Pb and some other undoped intermetallic compounds based on ytterbium, cerium, and europium indicates that hybridized electronic states occurring as the result of hybridization between the localized 4f electrons and the collectivized conduction electrons constitute a fundamentally new source of ESR.     

Structure of the highly deformed nucleus101Sr63 and evidence for identical K=3/2 bands

The low-energy level scheme of theN=63 nucleus¹⁰¹Sr has been obtained from a β-decay study of¹⁰¹Rb. The ν[532]5/2 and ν[411]3/2 orbitals are well established as the ground state and a band head at 271.2keV, respectively. The general properties of the level scheme indicate a quadrupole deformation ofβ ? 0.4, confirming the unique feature of saturation of deformation inN ≥ 60 Sr isotopes. The energies of theK=3/2 intraband transitions in the odd-neutron neighbours⁹⁹Sr₆₁ and¹⁰¹Sr₆₃ are very similar. More generally, the identical bands at low spin in^98–101Sr nuclei are correlated with the mass-independent moments of inertia in this region.     

Orbital-decomposed electronic and magnetic properties of the double perovskite Sr2FeReO6

The detailed orbital-decomposed electronic structures and magnetic properties of the double perovskite Sr₂FeReO₆ have been studied using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). Both occupied and unoccupied s and three p states of Fe³⁺ ion are located far away from the Fermi level, while all up-spin states and most down-spin states are completely filled for the s and three p states of Re⁵⁺ ion. The octahedral crystal field of the oxygen atoms around transition-metal (TM) sites splits the five-fold degenerate d states of the free TM atoms into triply degenerate t_2g states with smaller bonding-antibonding splitting and doubly degenerate e_g states with larger bonding-antibonding splitting. The Fe³⁺ and Re⁵⁺ ions are in the states (3d⁵, S=5/2) and (5d², S=1) with magnetic moments 3.70 and −0.86μ_B, respectively and thus antiferromagnetic coupling via oxygen between them. There are no direct interactions between two nearest Fe-Fe or Re-Re pairs, whereas along each Fe-O-Re-O-Fe or Re-O-Fe-O-Re chains, the hybridizations between Fe 3d and 4s, O 2s and 2p, as well as Re 5p, 5d and 6s orbitals are fairly significant.     

Unconventional superconductivity and magnetism in Sr2RuO4 and related materials

We review the normal and superconducting state properties of the unconventional triplet superconductor Sr₂RuO₄ with an emphasis on the analysis of the magnetic susceptibility and the role played by strong electronic correlations. In particular, we show that the magnetic activity arises from the itinerant electrons in the Ru d‐orbitals and a strong magnetic anisotropy occurs (χ^+‐ < χ^zz) due to spin‐orbit coupling. The latter results mainly from different values of the g‐factor for the transverse and longitudinal components of the spin susceptibility (i.e. the matrix elements differ). Most importantly, this anisotropy and the presence of incommensurate antiferromagnetic and ferromagnetic fluctuations have strong consequences for the symmetry of the superconducting order parameter. In particular, reviewing spin fluctuation‐induced Cooper‐pairing scenario in application to Sr₂RuO₄ we show how p‐wave Cooper‐pairing with line nodes between neighboring RuO₂‐planes may occur. We also discuss the open issues in Sr₂RuO₄ like the influence of magnetic and non‐magnetic impurities on the superconducting and normal state of Sr₂RuO₄. It is clear that the physics of triplet superconductivity in Sr₂RuO₄ is still far from being understood completely and remains to be analyzed more in more detail. It is of interest to apply the theory also to superconductivity in heavy‐fermion systems exhibiting spin fluctuations.     

Nd2Fe14B的价电子结构分析和磁性计算

应用固体与分子经验电子理论计算了Nd₂Fe₁₄B的价电子结构、磁矩和居里温度,计算结果与实验值相符.计算表明:该合金的磁性与3d磁电子数成正比.从Fe(c)晶位到Fe(k₂)晶位磁矩增加,其机理源于价电子、哑对电子和3d磁电子之间的转化,有78%的哑对电子和18%的3d共价电子转化成了磁电子.居里温度和磁矩与Fe原子配位数成正比,与加权等同键数I^σ成反比,Nd原子 关键词： 2Fe₁₄B')" href="#">Nd₂Fe₁₄B 价电子结构 居里温度     

First-principles research on influence of C dopants on magnetic and electric properties of rocksalt MgS

<正>The 2×2×1 rocksalt C-doped MgS supercells are optimized and their magnetic and electric properties,including the half-metallicity,the conductivity and the supercell magnetic moments,are calculated or analysed by the first-principles researches based on the density functional theory.Results show that the concentration of C-dopants may cause important influence on the magnetic and the electric properties of rocksalt MgS.C dopants are inclined to have a scattering distribution.MgC_(0.0625)S_(0.9375),~aMgC_(0.1250)S_(0.8750) and MgC_(0.1875)S_(0.8125) have evident half-metallicity. They have wide spin energy gaps,thus high Curie temperature possibly.Their supercell magnetic moments are near to integral numbers 2.0,4.0 and 6.0μB.The main reason for spin polarization and half-metallicity of C-doped MgS is that there are sp hybridized orbitals in ligand compound ML_6 caused by covalent interaction between C-ions and Mg-ions.     

Roles of the band filling and the d orbitals hybridization on the conduction and magnetism of some Sr-based double perovskites: An LSDA+U study

We have systematically investigated the electronic structure and magnetic properties of the double perovskite oxides Sr₂CrZrO₆, Sr₂MnNbO₆, Sr₂FeMoO₆ and Sr₂NiRuO₆ in terms of band filling of different t_2g and e_g orbitals. Calculations of density of the states (DOS) were performed within the frame of the local spin density approximation and Hubbard potential (LSDA+U) employed in the Linear Muffin Tin Orbitals with Atomic Sphere Approximation (LMTO-ASA) method. The DOS of Sr₂FeMoO₆ was obtained and found to agree very well with published reports. Half-metallic character through the spin-down channel and the ferrimagnetic ordering was observed with notable hybridization among the 3d, p and 4d orbitals within Fermi level. A difference between the theoretically expected values and the calculated ones for the magnetic moment (Δm) of the 3d orbitals is determined and had been found to increase on going from Sr₂CrZrO₆ to Sr₂NiRuO₆. This increment in Δm indicates increment in the hybridization strength, which leads to long range ordering in Sr₂FeMoO₆ and Sr₂NiRuO₆ compounds. In comparison with reported experiments, the frustrated magnetism and weak ferrimagnetism states are the most possible ones in Sr₂CrZrO₆ in Sr₂MnNbO₆, respectively. The half-metallic character was also seen in Sr₂MnNbO₆ and Sr₂CrZrO₆ compounds while Sr₂NiRuO₆ shows normal metallic conduction and ferromagnetism in accordance with the superexchange interaction e_g²-o-e_g⁰ of Goodenough-Kanamori-Anderson (GKA).     

Electronic structural and magnetic properties of cadmium chalcogenide beryllosilicate sodalites

Density functional self-consistent spin-polarized calculations with the Discrete Variational Method were performed to obtain the electronic structures of cadmium chalcogenide beryllosilicate sodalites Cd₈[BeSiO₄]₆Z₂ and their bulk materials CdZ (Z = S, Se, Te). Similar as their bulk materials, these sodalites are also semiconductors. From their density of states and charge distributions, it was found that there is greater localization of the electron density in the sodalites compared with that of the bulk. The band gaps in their bulk compounds are different from those in the sodalite structures due to the electrons of Si, Be and O filled in. Different from their bulk materials, the d electrons of Cd play an important role to form an unseparated valence band with all orbitals of other elements. The calculated magnetic moments of these three materials are very small since all d atomic orbitals are fully occupied. Received: 28 March 1997 / Revised: 18 July 1997 / Accepted: 9 September 1997     

Probing the structural,bonding, electronic and magnetic properties of transition–metal borazine systems: Co m (borazine) n (m = 1, 2; n = 1–3)

ABSTRACT

The geometrical structures of neutral and anionic Co _m (borazine) _n (m?=?1, 2; n?=?1–3) complexes have been determined by using density functional theory. The results indicate that most of the ground state structures for the complexes are similar to those of Co _m (benzene) _n , which might because borazine is isoelectronic and isostructural to benzene. The frontier molecular orbitals (FMOs) analyses show that their FMOs mainly arise from the 3d/4s electrons of cobalt atoms and the weak π-cloud of borazine molecule. Furthermore, the magnetic moments of complexes were studied and the results revealed that the Co atoms carry most of the magnetic moments. Comparing with the magnetic moment of a free Co atom (3.0μ_B), the magnetic moments of Co atom in most of Co _m (borazine) _n ^0/- complexes are significantly reduced and even quenched except that the Co(borazine) remains unchanged. More importantly, there is a transition FM-to-AFM between neutral and anionic Co₂(borazine)₂. Finally, natural population analyses were performed to insightfully explore the reliable electronic structure properties.     

Reentrant superconductivity in the orthorhombic system (Tm1−xLux)RuB2

The boundaries between the paramagnetic, superconducting and magnetically ordered phases in the orthorhombic pseudoternary system (Tm_1?xLu_x)RuB₂ have been established by means of ac magnetic susceptibility measurements down to 1.2 K. Reentrant superconductivity occurs between x = 0.52 and x ? 0.68. The absence of coexistence between superconductivity and long range magnetic order in this region suggests a ferromagnetic-like nature of the magnetic state. The initial linear depression of superconducting transition temperature (T_c) gives a coupling constant value N(E_F)$\text{J}$² between conduction electrons and magnetic Tm³⁺ moments of 6.7 × 10^?4 eV-atom-states/ spin direction.     

Magnetic structure of the Sr<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>4</Subscript>Cl<Subscript>2</Subscript> two-subsystem antiferromagnet according to nuclear quadrupole resonance data

The magnetic structure of the Sr₂Cu₃O₄Cl₂ two-subsystem antiferromagnet is studied by the nuclear quadrupole resonance (NQR) method on the ^{63, 65}Cu and ³⁵Cl nuclei. The resonance spectrum above T _N2 = 40 K is determined by the Zeeman splitting of the levels of the ^{63, 65}Cu nuclei of the copper atoms at the Cu1 site with the first-order quadrupole perturbation. The magnetic field on the copper nuclei is equal to 93 kOe. The spectrum below n is significantly different: it includes a low-frequency part, which is associated with the ordering of the second magnetic subsystem Cu2. The splitting of the NQR lines of ³⁵Cl is observed above and below T _N2. This fact indicates the ferromagnetic ordering of the moments of the Cu1 subsystem, which are located along the c axis of the crystal, and makes it possible to determine the direction of the magnetic field on Cu1 copper as (110).     

Effect of doping by boron,carbon, and nitrogen atoms on the magnetic and photocatalytic properties of anatase

The effect of doping of titanium dioxide with the anatase structure by boron, carbon, and nitrogen atoms on the magnetic and optical properties and the electronic spectrum of this compound has been investigated using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) band-structure method in the local spin density approximation explicitly including Coulomb correlations (LSDA + U) in combination with the semiempirical extended Hückel theory (EHT) method. The LSDA + U calculations of the electronic structure, the imaginary part of the dielectric function, the total magnetic moments, and the magnetic moments at the impurity atoms have been carried out. The diagrams of the molecular orbitals of the clusters Ti₃ X (X = B, C, N) have been calculated and the pseudo-space images of the molecular orbitals of the clusters have been constructed. The effect of doping on the nature and origin of photocatalytic activity in the visible spectral range and the specific features of the generation of ferromagnetic interactions in doped anatase have been discussed based on the analysis of the obtained data. It has been shown that, in the sequence TiO_{2 ? y} N _y → TiO_{2 ? y} C _y → TiO_{2 ? y} B _y (y = 1/16), the photocatalytic activity can increase with the generation of electronic excitations with the participation of impurity bands. The calculated magnetic moments for boron and nitrogen atoms are equal to 1 μ_B, whereas the impurity carbon atoms are nonmagnetic.     

Ferromagnetic half-metallic characteristic in bulk Ni0.5M0.5O (M=Cu,Zn and Cd): A GGA+U study

Ferromagnetic half metallicity with a high spin polarization of 100% was predicted in the bulk Ni_0.5Cu_0.5O using density-functional theory method. The band gap of majority spin is 3.45 eV for Ni_0.5Cu_0.5O. The density of states of minority spin at the Fermi level are mainly from Cu 3d and O 2p in the Ni_0.5Cu_0.5O. The magnetic moments are from Ni 3d states. Ni_0.5Zn_0.5O and Ni_0.5Cd_0.5O systems are ferromagnetic insulators, but the magnetic moment of Ni²⁺ ions is enhanced by the Zn and Cd incorporation. Therefore, Ni_0.5Cu_0.5O is the potential candidate for spintronics devices because of the predicted high spin polarization.     

A new study on the catalytic mechanism of Fe-based alloys in diamond formation by Mössbauer spectroscopy

M?ssbauer spectroscopy has been used to systemically study the catalytic mechanism of Fe-based alloys in diamond formation at high temperature–high pressure (HTHP) for the first time. M?ssbauer spectra reveal the magnetic state of the 3d electrons of a Fe atom in the Fe-based alloy catalyst during diamond formation at HTHP. During carburization at lower temperatures than that required for diamond formation and diamond formation in the diamond-stability region using Fe-based alloys as a catalyst, both the quadrupole splitting QS and the isomer shift IS change from negative to positive, especially reaching a state in which they are zero. It was indicated that the state of the 3d-shell electrons of the iron atom changes greatly during carburization and diamond formation and that the incomplete 3d sub-bands of Fe atoms in the catalyst alloys could be filled up in proper order by electrons of interstitial carbon atoms. During diamond formation, the unpaired 3d-shell electrons of an iron atom in the Fe-based alloy absorb and interact with 2P_z electrons of the carbon atoms. There exist a Fe–C bonding and an electron charge transfer stage. The 2P_z electrons of the carbon atoms could be dragged into the metal atoms in the catalyst alloy and would make a transition of triangular (sp²π) hybridization of valence electrons to tetrahedral (sp³) hybridization of valence electrons (a transition of sp²π bonds of graphite to sp³ bonds of diamond), resulting in a transition of graphite structure to diamond. Although the conclusion of this study is strictly applicable only to Fe-based alloy catalysts, it could be considered more general because of the chemical similarities between the transition elements used as solvent catalysts for diamond synthesis. Received: 2 March 2001 / Accepted: 20 August 2001 / Published online: 2 October 2001     

Superhyperfine structure in the EPR spectra and optical spectra of impurity f ions in dielectric crystals: A review

The results of observation and simulation of the superhyperfine (ligand hyperfine) structure (SHFS) of the electron paramagnetic resonance (EPR) spectra of rare-earth and uranium impurity ions in dielectric crystals have been systematized. The resolved SHFS of the EPR spectra of doped cubic crystals (with the fluorite and perovskite structures) has been observed for orientations of a constant magnetic field along the crystallographic axes. Most attention has been paid to tetragonal double fluorides LiRF₄ (R = Y, Lu, Tm), in which the SHFS of the EPR spectra has also been found for intermediate orientations of the magnetic field. For the LiYF₄: Nd³⁺ single crystal, the splitting of optical spectral lines due to the interaction of Nd³⁺ ions with nuclear magnetic moments of the nearest neighbor fluorine ions has been observed for the first time. The Van Vleck paramagnet LiTmF₄: U³⁺ is characterized by the SHFS with clearly distinguishable components due to the interaction of uranium ions both with nuclei of the fluorine ions and with enhanced magnetic moments of the thulium nuclei. The SHFS envelopes of the EPR spectra of Yb³⁺, Ce³⁺, Nd³⁺, and U³⁺ ions in LiYF₄ and LiLuF₄ crystals are well reproduced by numerical calculations based on the microscopic model using only three fitting parameters: the width of transitions between the electron-nuclear sublevels of the complex containing the paramagnetic ion and nuclei of the ligands and two constants of covalent bonding of the f electrons with 2s and 2p electrons of the nearest neighbor fluorine ions.     

Infrared spectroscopic study of thermal annealing effects of hydrocarbon species on a Si surface exposed to methane plasma

We have investigated the thermal annealing effects of hydrocarbon species on the methane-plasma exposed silicon surface, investigated by in situ infrared absorption spectroscopy (IRAS) in multiple internal reflection (MIR) geometry. The proportion of types of hydrocarbon species is not remarkably changed in the hydrocarbon network that consists of sp-, sp²- and sp³-CH_X species by annealing at moderate temperatures. On the other hands, the proportion is drastically changed in the network that is mainly composed of sp³-CH_X species by annealing at moderate temperatures. It suggests that excess CH₃ species in the film is not stable against thermal annealing and would be converted to sp³-CH_1-2 species by annealing at moderate temperatures. And the data also show that sp²-CH species is more stable against the thermal annealing than sp³-hydrocarbon species.     

Charge Distribution and Hyperfine Interactions in the CuFeO<Subscript>2</Subscript> Multiferroic According to <Superscript>63,65</Superscript>Cu NMR Data

For the first time, the CuFeO₂ single crystal has been studied by ^63,65Cu nuclear magnetic resonance (NMR). The measurements have been carried out in the temperature range of T = 100?350 K in the magnetic field H = 117 kOe applied along different crystallographic directions. The components of the electric field gradient tensor and the hyperfine coupling constants are determined. It is shown that electrons of copper 4s and 3d orbitals are involved in the spin polarization transfer Fe → Cu. The occupancies of these orbitals are estimated.     

a-C∶H(N)薄膜结构的X射线光电子能谱分析

采用直流-射频等离子增强化学汽相沉积技术制备a-C∶H(N)薄膜，用X射线光电子能谱研究了混合气体中N₂含量对薄膜成分与结构的影响.a-C∶H(N)薄膜中含氮量可达9.09%.对a-C∶H(N)薄膜的C1s和N1s结合能谱的分析表明a-C∶H(N)薄膜的结构是由C₃N₄相镶嵌在sp²键结合的CN_x基体中组成.其中C₃N₄相中N和C原子比接近4∶3，不随薄