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101.
We present a theory of orbital ordering in orbital-degenerate itinerant electron systems. The orbital instability in a two-orbital degenerate Hubbard model is investigated in the random phase approximation (RPA). After demonstrating the criteria for the formation of orbital ordering or the orbital density wave ordering, we find that the orbital and the spin-orbital collective excitation spectra in the ferro-orbital ordered phase exhibit finite gaps. The possible application of the present theory in orbital-ordered 4d compounds is also discussed. 相似文献
102.
High-frequency magnetic properties and attenuation characteristics for barium-ferrite/epoxy composites have been studied. The methods for increasing μ′ and μ″ and controlling fR, including ion substitution, doping of small amount of oxides, effect of damping, as well as the modification of particle sizes and shapes, are introduced. The results show that the composites are potential candidates for use as electromagnetic (EM) attenuation materials with low reflectivity and broad bandwidth at 2-18 GHz. 相似文献
103.
R?za Erdem 《Journal of magnetism and magnetic materials》2009,321(17):2592-2595
The complex susceptibility or the dynamic susceptibility (χ(ω)=χ′(ω)−iχ″(ω)) for a spin-1 Ising system with bilinear and biquadratic interactions is obtained on the basis of Onsager theory of irreversible processes. If the logarithm of the susceptibilities is plotted as a function of the logarithm of frequency, then the real part (χ′) displays a sequence of plateau regions and the imaginary part (χ″) has a sequence of maxima in the ordered or ferromagnetic phase. On the other hand, only one plateau region in χ′ and one maximum in χ″ is observed in the disordered or paramagnetic phase. Argand or Cole-Cole plots (χ″−χ′) for a selection of temperatures are also shown, and a sequence of semicircles is illustrated in the ordered phase and only one semicircle for the disordered phase in these plots. 相似文献
104.
R.L. Rodríguez-Suárez F.M. de Aguiar 《Journal of magnetism and magnetic materials》2009,321(17):2596-2600
The magnetization dynamics of magnetic nanostructures magnetized at an arbitrary out-of-plane angle is investigated with the spin-wave formalism. The magnetic excitations driven by a spin-polarized direct current are considered to be standing spin-wave modes appropriate for nanopillar structures. The spin waves grow exponentially above a certain critical value of the current density and their post-threshold nonlinear dynamics leads to magnetization oscillations in the microwave range. Due to demagnetizing fields, the current-driven excitation strongly depends on the direction of the applied external magnetic field. In order to calculate the microwave oscillation frequency we derive an equation of motion for the spin-wave amplitude as a function of the out-of-plane angle of the applied field. The results are compared with recent experimental data as well as with another theoretical approach. 相似文献
105.
D. V. Vyalikh K. Kummer A. Kade A. Blüher B. Katzschner M. Mertig S. L. Molodtsov 《Applied Physics A: Materials Science & Processing》2009,94(3):455-459
We applied resonant photoemission and X-ray absorption spectroscopy for a detailed characterization of the valence electronic
structure of the regular two-dimensional bacterial surface protein layer of Bacillus sphaericus NCTC 9602. Using this approach, we detected valence electron emission from specific chemical sites. In particular, it was
found that electrons from the π clouds of aromatic systems make large contributions to the highest occupied molecular orbitals. 相似文献
106.
B. Bourahla A. Khater R. Tigrine 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):343-349
This paper describes a theoretical study, at a microscopic scale, of the
properties of a symmetric magnetic nanocontact. In particular, we study a
symmetric nanocontact separating two waveguide groups of semi-infinite spin
ordered ferromagnetic monatomic chains. The individual and total conductance
of bulk magnons of the chains, scattering coherently at the nanocontact, and
the localised density of spin states in the nanocontact domain, are
calculated and analysed. The inter-atomic magnetic exchange is varied on the
nanocontact to investigate the consequences of magnetic softening and
hardening for the calculated properties. Transmission and reflection
scattering cross sections are calculated from elements of a Landauer type
scattering matrix. The results highlight the localized spin states on the
nanocontact domain and their interactions with incident magnons. The results
demonstrate also the magnetic and symmetry properties of the nanocontact
domain. 相似文献
107.
A new experimental method for the determination of the Landau–Lifshitz damping parameter, α, based on measurements of the frequency and field dependence of the complex magnetic susceptibility, χ(ω,H)=χ′(ω,H)-iχ″(ω,H), is proposed. The method centres on evaluating the ratio of fmax/fres, where fres is the resonance frequency and fmax is the maximum absorption frequency at resonance, of the sample susceptibility spectra, measured in strong polarizing fields. We have investigated three magnetic fluid samples, namely sample 1, sample 2 and sample 3. Sample 1 consisted of particles of Mn0.6Fe0.4Fe2O4 dispersed in kerosene, sample 2 consisted of magnetite particles dispersed in Isopar M and sample 3 was composed of particles of Mn0.66Zn0.34Fe2O4 dispersed in Isopar M . The results obtained for the mean damping parameter of particles within the magnetic fluid samples are as follows: 〈α(Mn0.6Fe0.4Fe2O4)〉=0.057 with the corresponding standard deviation SD=0.0104; 〈α(Fe3O4)〉=0.1105 with the corresponding standard deviation, SD=0.034 and 〈α(Mn0.66Zn0.34Fe2O4)〉=0.096 with the corresponding standard deviation, SD=0.037. 相似文献
108.
Polyimide (PMDA-ODA) surface was irradiated by low energy reactive atomic beam with energy 160-180 eV to enhance the adhesion with metal Cu film. O2+ and N2+ ions were irradiated at the fluence from 5 × 1015 to 1 × 1018 cm−2. Wetting angle 78° of distilled deionized (DI) water for bare PI was greatly reduced down to 2-4° after critical ion flounce, and the surface energy was increased from 37 to 81.2 erg/cm. From the analysis of O 1s core-level XPS spectra, such improvement seemed to result from the increment of hydrophilic carbonyl oxygen content on modified PI surface. To see more carefully correlation of the peel strength with interfacial reaction between Cu and PI, flexible copper clad laminate with Cu (9 μm)/Cu (200 nm) on modified PI substrate (25 μm) was fabricated by successive sputtering and electroplating. Firstly, peel strength was measured by using t-test and it was largely increased from 0.2 to 0.5 kgf/cm for Ar+ only irradiated PI to 0.72-0.8 kgf/cm for O2+ or N2O+ irradiated PI. Chemical reaction at the interface was reasoned by analyzing C 1s, O 1s, N 1s, and Cu 2p core-level X-ray photoelectron spectroscopy over the as-cleaved Cu-side and PI side surface through depth profiling. From the C 1s spectra of cleaved Cu-side, by the electron transfer from Cu to carbonyl oxygen, carbonyl carbon atom became less positive and as a result shifted to lower binding energy not reaching the binding energy of C2 and C3. The binding energy shift of the peak C4 as small as 1.7 eV indicates that carbonyl oxygen atoms were not completely broken. From the analysis of the O 1s spectra, it was found that new peak at 530.5 eV (O3) was occurred and the increased area of the peak O3 was almost the same with reduced area of the peak carbonyl oxygen peak O1. Since there was no change in the relative intensity of ether oxygen (O2) to carbonyl oxygen (O1), and thus O3 was believed to result from Cu oxide formation via a local bonding of Cu with carbonyl oxygen atoms. Moreover, from X-ray induced Auger emission spectra Cu LMM which was very sensitive to chemical bonding, Cu oxide or CuOC complex formation instead of CuNO complex was clearly identified by the observation of the peak at 570 eV at higher 2 eV than that of metal Cu. In conclusion, when Cu atoms were sputtered on modified PI by low energy ion beam irradiation, it can be suggested that two Cu atoms locally reacted with carbonyl oxygen in PMDA units and formed Cu+O−C complex linkage without being broken from carbon atoms and thus the chemically bound Cu was in the form of Cu2O. 相似文献
109.
F. Ricoul M. Dubois T. Zemb D. Plusquellec 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):333-340
By use of a mean-field approach the spin-wave dispersion of the Cu degrees of freedom in the undoped high-T C material Nd2CuO4is investigated. The experimentally observed sharp decrease of the Cu spin-wave gap with increasing temperature in the range
is explained by a paramagnetic-like susceptibility of the Nd spins which couple to the Cu subsystem. The degeneracy of the
“in-plane” and “out-of-plane” polarized Cu spin-wave branches is shown to be lifted by the uniaxial anisotropy of the Cu-Cu
nearest-neighbor interaction.
Received: 13 August 1997 / Revised: 4 December 1997 / Accepted: 11 December 1997 相似文献
110.
We study the melting of incommensurate soliton lattice using the exact Bethe ansatz solution of one-dimensional quantum sine-Gordon Hamiltonian with U(1) coupling. The elastic moduli of soliton lattice are obtained and their asymptotic behaviors are explicitly calculated both at zero and finite temperature. We have obtained the thermodynamic phase boundaries of the soliton lattice and shown that the direct commensurate-incommensurate transitions are intervened by the fluid phase for T>0 as predicted by Coppersmith et al. [Coppersmith et al., Phys. Rev. Lett. 46 (1981) 549. [1]] for n≤2. 相似文献