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1.
The variation of the Néel temperature (TN) of antiferromagnetic alloys of Mn with 3-d elements has been studied by electrical resistivity measurements. Binary Mn-rich alloys Fe, Co, Ni, Ti, Rh, Os, Ir, and Ru were investigated. The results show a strong and systematic dependence on the number of d-electrons of the impurity element. Elements with more d electrons than Mn raise TN, while those with fewer d electrons depress TN. The change of TN per atomic percent impurity also exhibits a striking, non-monotonic dependence on the impurity used. The dependence shows inversion symmetry with impurities around Mn.To further elucidate the properties of the Mn-rich antiferromagnetic system, a study was made of ternary Mn-rich alloys in the MnFeCr, MnCoNi, and MnVTi systems. The results from the MnFeCr system are consistent with the rigid-band model, the average number of d-electrons per atom being of primary importance determiningh the antiferromagnetism in this system.Our goal in these studies has been to provide a firm experimental data baseupon which future theoretical work can be built. A more detailed understanding of the very intriguing α-Mn magnetic system now awaits further theoretical investigation. 相似文献
2.
采用密度泛函理论和平面波赝势方法对含天然杂质黄铁矿的电子结构和光学性质进行了计算,并讨论了二十种天然杂质:钴、镍、砷、硒、碲、铜、金、银、钼、锌、铊、锡、钌、钯、铂、汞、镉、铋、铅和锑,对黄铁矿催化活性的影响.结果表明在过渡金属杂质中,杂质能级主要由它们的d轨道产生,而在主族金属及非金属杂质中,杂质能级主要由它们的s或p轨道产生.含铜、钼、砷、金、银或镍的黄铁矿对氧的还原的电催化能力增强.除锌、钼、钌、砷、锑、硒和碲外,其余杂质能增强黄铁矿表面俘获电子的能力,使光生电子和空穴复合的概率减小.光学性质计算表
关键词:
天然黄铁矿
杂质
电子结构
光学性质 相似文献
3.
We have performed first-principles calculations on the structural, electronic and magnetic properties of seven different 3d transition-metal (TM) impurity (V, Cr, Mn, Fe, Co, Ni and Cu) doped armchair (5,0) and zigzag (8,0) gallium nitride nanotubes (GaNNTs). The results show that there is distortion around 3d TM impurities with respect to the pristine GaNNTs for 3d TM-doped (5,5) and (8,0) GaNNTs. The change of total magnetic moment follows Hund’s rule for 3d TM-doped (5,5) and (8,0) GaNNTs, respectively. The total density of states (DOS) indicates that Cr-, Mn-, Fe- and Ni-doped (5,5) GaNNTs as well as Cr-, Mn-, Ni- and Cu-doped (8,0) GaNNTs are all half-metals with 100% spin polarization. The study suggests that such TM-doped nanotubes may be useful in spintronics and nanomagnets. 相似文献
4.
The effect of magnetic Ni and non-magnetic Zn impurities on superconducting transition temperature Tc in RuSr2R(Cu1?x(Ni, Zn)x)2O8 with R = Gd or Eu (Ni- and Zn-substituted Ru1212Gd(Eu)) was extensively studied. It is found that the suppression rate dTc/dx of RuSr2R(Cu1?x(Ni, Zn)x)2O8 is comparable to that of underdoped YBa2(Cu1?x(Ni, Zn)x)3O7?δ. The suppression of superconductivity in Ni-substituted Ru1212Eu samples is more significant than that in Zn-substituted ones, indicative of Ni being a more effective pair-breaker than Zn. In strong contrast, the magnetic Ni impurity atoms have a weaker effect on superconductivity than non-magnetic Zn atoms in Ru1212Gd, similar to what was observed in the high-Tc cuprates. These intriguing findings strongly suggest that the impurity-induced local disturbance of the 3d-spin correlation at Cu sites around Ni/Zn is distinctly different between Ru1212Gd and Ru1212Eu. 相似文献
5.
V. Simonet B. Grenier F. Villain A.-M. Flank G. Dhalenne A. Revcolevschi J.-P. Renard 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(2):155-167
The chemical selectivity and great sensitivity of the
Extended X-ray Absorption Spectroscopy technique allowed the
determination, in the paramagnetic phase, of the structural
distortions induced by doping in the spin-Peierls CuGeO3
compound. The distorted environments were analyzed as a function
of concentration, magnetic nature of impurity and the substitution
site (Ni, Mn and Zn impurities on the Cu site, Si impurity on the
Ge site). This has led to estimate the variation of the angles and
pair distances, and hence to evaluate the magnetic coupling along
the Cu chains in the vicinity of the impurities. The
antiferromagnetic interaction between Cu first neighbors in the
pure sample is found to be weakened around Ni, almost cancelled in
the case of Mn doping, and even to change sign, producing a
ferromagnetic coupling for Si doping. More generally, the
structural distortions on a local scale are shown to be key
parameters for the understanding of the magnetic properties of
doped spin-Peierls compounds. 相似文献
6.
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. 相似文献
7.
We use ab initio calculations to investigate spin and orbital moments of 3d transition-metal adatoms and Co nanostructures on Cu(0 0 1) surfaces. For Fe and Co adatoms on Cu(0 0 1) we predict extremely large orbital moments, comparable to the spin moments at these sites. For Mn and Cr adatoms the orbital moments are extremely small and can be neglected in face of their rather large spin moments. Ni adatoms on Cu(0 0 1) were found to be non-magnetic. Our investigations for adsorbed flat clusters of Co on Cu(0 0 1) address the persistence and extent of these large orbital moments in the clusters as a function of their size. We find that, the average orbital moment (Morb) per Co atom is strongly correlated with the coordination number, decreasing drastically and monotonically as the average number of first Co neighbors around the sites in the cluster (NCo) is increased. 相似文献
8.
Indium selenide belongs to layered III–VI semiconductors with highly anisotropic optical and electronic properties. Energy gap of 1.32 eV makes this material very attractive for solar energy conversion. We investigated the influence of 1% 3-d transition metals M=Mn, Fe, Co, Ni, used as dopants, on energy levels of InSe:M in the range 1.4–6.5 eV and especially in the range of energy gap <1.4 eV by means of ellipsometric measurements. It was concluded that at ambient temperature foregoing dopants, all divalent, with 4s2 valent electrons, in the similar way influenced on blue-shift of energy levels in valent zone, but did not influence on the fundamental energy gap. Photoluminescence measurements confirmed blue-shift of the valent zone energy levels and an existence of deep impurity levels. 相似文献
9.
Gwyn Williams 《Solid State Communications》1974,14(7):649-652
Existing data on the depression of the superconducting transition temperature of Ru by Co, Ni, Ft, Pd, Rh and Ir impurities are analysed using Kaiser's model, which considers resonant scattering from non-magnetic impurity states. Numerical values for various parameters characterising this resonant d-state are thus derived; in particular estimates of the intra-impurity Coulomb repulsion are obtained from which the presence (or absence) of localised spin fluctuations in these alloy systems is inferred. 相似文献
10.
The effect of Co, Ni and Zn substitutions for Cu on the phase stability and superconducting properties of (Hg0.7Cr0.3)Sr2CuO4+δ was investigated. X-ray diffraction (XRD) revealed that both Co and Zn are soluble in the (Hg0.7Cr0.3)Sr2CuO4+δ material up to about 5% of the Cu content, whereas the solubility of Ni is extended up to 10%. Electrical resistivity and magnetic susceptibility measurements show that the value of the superconducting critical temperature Tc decreases linearly with the impurity content. The depression of Tc indicates that the suppression of the superconductivity in Co- and Ni-substituted samples is much stronger than that in Zn-substituted ones. The residual resistivity scales linearly with the doping level as expected from the impurity scattering due to disorder. Some possible explanations for the stronger suppression of Tc by the Co and Ni substitution than by Zn substitution are provided. 相似文献
11.
The electronic structure of 3d transition-metal atoms on face-centered cubic Co(0 0 1) substrate is determined within ab initio density functional calculations in the gradient corrected approach. Calculations are performed for ordered surface configuration with coverage equal to 0.25, 0.5, 0.75 and 1 ML. For Ni and Fe a ferromagnetic coupling with the Co atoms is always obtained independently of the concentration. Moreover the values of the magnetic moments remain similar. For Mn a ferromagnetic coupling is obtained for low-coverage whereas an in-plane antiferromagnetic coupling is found for a complete Mn overlayer on Co(0 0 1). Also, for Sc, Ti, V and Cr a drastic modification of the magnetic map is observed when we go from low-coverage to the monolayer. Cr (Mn) adatoms present antiferromagnetic (ferromagnetic) coupling with Co(0 0 1) for x = 0.25 whereas an in-plane antiferrimagnetic coupling is obtained for x = 1.00. 相似文献
12.
Opeil CP Mihaila B Schulze RK Mañosa L Planes A Hults WL Fisher RA Riseborough PS Littlewood PB Smith JL Lashley JC 《Physical review letters》2008,100(16):165703
Ultraviolet-photoemission (UPS) measurements and supporting specific-heat, thermal-expansion, resistivity, and magnetic-moment measurements are reported for the magnetic shape-memory alloy Ni2MnGa over the temperature range 100T(PM) is due to the Ni d minority-spin electrons. Below T(M) this peak disappears, resulting in an enhanced density of states at energies around 0.8 eV. This enhancement reflects Ni d and Mn d electronic contributions to the majority-spin density of states. 相似文献
13.
Jun Sasaki N.L. Peterson K. Hoshino 《Journal of Physics and Chemistry of Solids》1985,46(11):1267-1283
By means of the radioactive-tracer sectioning technique, the tracer diffusion of the impurity ions, 46Sc, 51Cr, 54Mn, 59Fe, 60Co, 63Ni and 95Zr, in rutile single crystals was measured as functions of crystal orientation, temperature, oxygen partial pressure and Al impurity content. The diffusion coefficients are very sensitive to the electric charge of the impurity ions. Divalent impurities (e.g., Co and Ni) diffuse extremely rapidly in TiO2, compared to cation self-diffusion, and exhibit an extreme anisotropy in diffusion behavior, divalent-impurity diffusion parallel to the c-axis is much larger than it is perpendicular to the c-axis. Trivalent impurity ions (Sc and Cr) and tetravalent impurity ions (Zr) diffuse similar to cation self-diffusion, both as functions of temperature and oxygen partial pressure. The divalent impurity ions Co and Ni apparently diffuse as interstitial ions along open channels parallel to the c-axis. The results suggest that Sc, Cr and Zr ions diffuse by an interstitialcy mechanism involving the simultaneous and cooperative migration of tetravalent interstitial titanium ions and the tracer-impurity ions. Iron ions diffuse both as divalent and as trivalent ions. The impurity diffusion as functions of oxygen partial pressure and Al-impurity content are consistent with calculations of point-defect concentrations in rutile. 相似文献
14.
The possibility of forming surface films with an elevated concentration of an impurity metal during high-temperature diffusion has been analyzed for a wide series of ionic crystals: LiF with Co, Ni, Mg, Ca, Ba, and Sr impurities; NaF with Co, Mn, Mg, Ca, and Sr; MgF2 with Co and Ni; and CaF2 with Co. It is established that films are formed only on alkali halide crystals with impurities of transition metals and are not formed on alkaline earth fluorides with transition metals, as well as on alkali halide crystals activated with other divalent cationic impurities. The dynamics of the increase and decrease in the intensity of centers related to impurity-vacancy dipoles during thermal diffusion is shown. The mechanisms of film formation are explained in terms of the features of growth and structure of ionic crystals with cationic impurities and on the basis of isomorphism rules. 相似文献
15.
Effects of the 3d transition metal doping on the structural,electronic, and magnetic properties of BeO nanotubes
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First-principles calculations have been performed on the structural, electronic, and magnetic properties of seven 3d transition-metal(TM) impurities(V, Cr, Mn, Fe, Co, Ni, and Cu) doped armchair(5,5) and zigzag(8,0) beryllium oxide nanotubes(BeONTs). The results show that there exists a structural distortion around the 3d TM impurities with respect to the pristine BeONTs. The magnetic moment increases for V- and Cr-doped BeONTs and reaches a maximum for Mn-doped BeONT, and then decreases for Fe-, Co-, Ni-, and Cu-doped BeONTs successively, consistent with the predicted trend of Hund’s rule to maximize the magnetic moments of the doped TM ions. However, the values of the magnetic moments are smaller than the predicted values of Hund’s rule due to the strong hybridization between the 2p orbitals of the near O and Be ions of BeONTs and the 3d orbitals of the TM ions. Furthermore, the V-, Co-, and Ni-doped(5,5) and(8,0) BeONTs with half-metal ferromagnetism and thus 100% spin polarization character are good candidates for spintronic applications. 相似文献
16.
We have measured the optical absorption of dilute AuTi alloys for photon energies from 0.1 to 4.5 eV. The extra absorption we observe below the Au interband threshold can be accounted for if the Ti impurities form virtual bound states with half-width at half height δ ~ 0.6 ± 0.2 eV centered Ed ~ 0.5 ± 0.2 eV above the Fermi level and containing 2.7 ± 0.3 electrons. 相似文献
17.
基于密度泛函第一性原理计算,系统研究了Mg12O12笼状团簇组装一维纳米线及其掺杂3d族元素体系的几何结构与电子结构。结果表明:Mg12O12团簇组装一维纳米线为非磁性半导体,带隙值为3.16 eV;掺杂Sc和V后,体系由半导体转变为金属;掺杂Ti、Cr、Mn、Fe、Co、Ni、Cu后体系仍然保持半导体特性、但带隙值明显减小,而掺杂Zn时带隙值变化不大;掺杂V、Cr、Mn、Fe、Co、Ni、Cu后纳米线具有磁性。 相似文献
18.
Mössbauer measurements were carried out in order to study the influence of the transition metal substitution TM/Fe (where TM = Co, Ni, Mn, and (TM)xFe3−xO4) ranging from 0.1 to 0.9 on the morphology and magnetic properties of ferrite nanoparticles. Chemically prepared magnetite nanoparticles with 13 nm were used as a reference material. The Mössbauer spectrum of the initial magnetite sample show a well-resolved magnetically split patterns connected with tetrahedral (A) positions and octahedral (B) positions. For low concentrations of TM, the relative intensities of the sextet that comes from the iron B position decrease. This means that the Co, Ni, Mn atoms are located preferentially in the B-site of the magnetite. However, the qualitative analysis of the spectra also suggests that Mn and Ni partially occupy the A-site. The increase of the concentration of the substitution transition metal causes broadening of the magnetic part of the spectra and appearance of a doublet in the central part of spectra for all samples. TEM studies show that the incorporation of the Me atoms into the structure causes a decrease of the average particle size. This is also confirmed by XRD. This also means that the blocking temperature decreases and for about Ni/Fe = 0.8 and TM/Fe = 0.9 (for Mn and Co) reaches room temperature. In the case of the nominal 0.9 substitution by Ni, a pure superparamagnetic state is observed, while for Co and Mn some of the particles are still below the blocking temperature, in agreement with the TEM studies. 相似文献
19.
We made Cu2ZnSnS4 (CZTS) thin films by sulfurization of Cu/Sn/Cu/Zn metallic films. Sulfurizations were carried out under different thermal annealing conditions, where maximum temperatures were 440 °C (LT-CZTS) and 550 °C (HT-CZTS). For LT-CZTS films, secondary phases such as SnS2 and Cu2?xS were observed, whereas for HT-CZTS films secondary impurities were not detected. Chemical composition of LT-CZTS film was observed to be very non-uniform. Highly Sn-rich and Zn-rich regions were found on the film surface of LT-CZTS. However, averaged chemical composition for larger area was close to stoichiometry. The HT-CZTS film showed homogeneous structural and chemical composition features. But, for HT-CZTS film, the Sn composition was observed to be decreased, which was due to the Sn-loss. By UV–Visible spectroscopy, optical band gaps of LT- and HT-CZTS films were measured to be ~1.33 eV and ~1.42 eV, respectively. The band gap of LT-CZTS film was also observed to be smaller by photoluminescence measurement. The depressed band gap of LT-CZTS film may be ascribed to some defects and low band gap impurities such as Cu2SnS3 and Cu2-xS in the LT-CZTS film. 相似文献
20.
We argue that the scanning tunneling microscope (STM) images of resonant states generated by doping Zn or Ni impurities into Cu-O planes of BSCCO are the result of quantum interference of the impurity signal coming from several distinct paths. The impurity image seen on the surface is greatly affected by interlayer tunneling matrix elements. We find that the optimal tunneling path between the STM tip and the metal (Cu, Zn, or Ni) d(x(2)-y(2)) orbitals in the Cu-O plane involves intermediate excited states. This tunneling path leads to the fourfold nonlocal filter of the impurity state in Cu-O plane that explains the experimental impurity spectra. Applications of the tunneling filter to the Cu vacancy defects and "direct" tunneling into Cu-O planes are also discussed. 相似文献