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Metal/polymer interfaces play an important role in polymeric light‐emitting diodes. Recent transport measurement studies by Parker promote a rigid band model with triangular barrier tunneling at the metal/polymer interface. This finding, however, stands in contradiction to the band bending and Schottky barrier formation observed using surface analytical techniques. We found that this apparent contradiction can be nicely reconciled if a modification of the tunneling model by band bending is included in the interpretation of the transport data. Band bending modified tunneling gives a clear physical picture of the tunneling process across the metal/polymer interface and is important for low field tunneling processes.

Al substitution effects on the magnetic properties of RCo5 (R=Y, Pr, Nd, and Sm) are studied on the basis of magnetic measurements for RCo5−xAlx with x less than 2. The Al substitution considerably decreases the Curie temperature, the Co‐sublattice moment, the magnetocrystalline anisotropy of the R sublattice as well as of the Co sublattice. The Co‐sublattice moments in RCo5−xAlx have a different value depending on their directions in the crystal; in addition the rare earth moments are considerably smaller than the values of their free trivalent ions. The decrease of Co‐sublattice moment with increasing content of Al can be explained by the rigid band model, and the properties of rare earth sublattices (or atoms) mentioned above seem to be explained by the exchange field at the rare earth site which weakens with increasing Al content.

To reveal the role of Fe sublattice in the coercivity of R2Fe14B, we investigated the origin of perpendicular magnetocrystalline anisotropy (MCA) of Y2Fe14B using first-principles density-functional calculations. We found that the perpendicular MCA of Y2Fe14B arises predominantly from Fe sites with higher symmetry (16k1,2 and 8j1,2). On the other hand, the Fe(4c) sites show a significant contribution to the in-plane MCA. This can be attributed to the localized character of Fe(4c)-d orbitals in R2Fe14B. Furthermore, the MCA energy of Y2Fe14B increases as the number of valence electrons increases within the rigid band model, indicating that the partial substitution of Fe by Co can enhance the MCA energy of Y2Fe14B.

Lattice instability of off-stoichiometric Ni-Mn-Ga based ferromagnetic shape memory alloys with different valence electron concentrations (e/a’s) has been studied by utilizing hard X-ray photoelectron spectroscopy. Comparison of two alloys with different e/a’s suggests that a rigid band model is not applicable to explain the different martensitic transition temperatures. It is revealed that the specimen with larger e/a shows larger density of the Ni 3d eg states near the Fermi energy compared to specimen with lower e/a. The results can be reasonably explained by the band Jahn-Teller effect.

The tuning of carrier concentration through chemical doping is very important for the optimization of thermoelectric materials. Traditionally, a rigid band model is used to understand and guide doping in such semiconductors, but it is not clear whether such an approximation is valid. This letter focuses on the changes in the electronic density of states (DOS) near the valence band maximum for different p-type dopants (Na, K, Tl, or vacancy on Pb site) maintaining the high symmetry of the NaCl structure. Na- and K-doped, and vacancy-introduced PbTe show a clear rigid-band like change in DOS unlike that concluded from supercell based calculations.

Hydrostatic-pressure (up to 0.96 GPa) dependence of Tc in a newly discovered Fe-based superconductor (Tl0.59Cs0.26)Fe1.9Se2 (Tc = 28 K, at ambient pressure) is reported. Static magnetization measurements under pressure indicate that the linear increase in Tc is initially rapid (dTc/dP ∼ 9.9 K · GPa−1) but slows down to dTc/dP ∼ 2.5 K · GPa−1 for P ≧ 0.18 GPa. The Tc of the superconducting phase is 32 K at pressure P = 0.96 GPa. The simple rigid band model or the Bardeen, Cooper, Schrieffer theory may not be sufficient to account for our observations, if one assumes that the lattice parameters would be linearly decreased with pressure.

The crystal structure, magnetic properties and magnetostriction of polycrystalline magnetostrictive alloys Nd(Fe1−xCox)1.9 were investigated. It was found that the single cubic Laves phase can only be obtained in the samples with x>0.4 by a traditional annealing method. In contrast, the cubic Laves phase exists over the entire composition range studied in the samples annealed under high pressure. Both the Curie temperature and saturation magnetization increase with increasing Co concentration to a maximum at x = 0.2 and then decrease with further increasing x, which could be understood in the frame of rigid band model. The spin phase diagram for Nd(Fe1−xCox)1.9 is constructed to illustrate the arrangement for the easy magnetization direction and crystal structure. The magnetostriction of Nd(Fe1−xCox)1.9 increases with increasing Co concentration and peaks at x = 0.1 and then presents an anomalous behavior when 0.2≤x≤0.6. It is suggested that the external-field-induced lattice strain should be responsible ...

Using the highly precise full potential linearized augmented plane wave method, we determined atomic structure and the magnetostriction of Fe100−xGax with x

Polycrystalline magnetostrictive alloys Pr(Fe1−xMnx)1.9 (0⩽x⩽0.2) were synthesized by high-pressure annealing. X-ray diffraction results show that all the samples exhibit cubic Laves phase with MgCu2-type structure. The lattice parameter increases with increasing Mn concentration while the Curie temperature decreases. The saturation magnetization decreases with increasing Mn concentration, which can be understood on the basis of the rigid band model. The magnetizations of the samples with x=0.05 and x=0.1 are easy to get saturated in comparison with that of the sample without Mn, which implies that small amount of substitution Mn for Fe can lower the magnetic anisotropy of the alloy. The saturation magnetostriction decreases monotonously with increasing Mn content, while the magnetostriction of the sample with x=0.1 shows a peak at low magnetic fields.

RCrSb3 (R: rare-earth ions) exhibits unconventional magnetic behaviors due to their layered structures and the complex interactions of Cr 3d and R 4f electrons. We have explored the electronic structures of LaCrSb3, YbCrSb3, and also LaVSb3 for a comparison by using the linearized muffin-tin orbital band method. For LaCrSb3 and LaVSb3, the rigid band model is well applicable to understanding their electronic and magnetic states. However, for LaCrSb3 and YbCrSb3, the extension of the rigid band model fails, because Yb ions in YbCrSb3 are in a divalent state of Yb2+ with fully occupied 4f bands, which differ from the trivalent La3+ in LaCrSb3.

The effects on the electronic structure and magnetic property of the Ni site substitution in nonoxide perovskite superconductor MgCNi3 are studied by using density functional calculations. A sharp high peak of Ni d density of states just lies below the Fermi energy in pure MgCNi3. Co-doping results in the onset of ferromagnetism at x=0.083. However, the little energy gain as well as small magnetic moment per atom indicate the weak itinerant ferromagnetism. The strong ferromagnetic spin fluctuation in MgCNi3−xCox leads to quench bulk superconductivity, while the Mn atom forms a local magnetic moment of 1.06 μB at x=0.042 which suppresses superconductivity more seriously than Co does in the low doping case. Cu doping can be well accounted for by the rigid band model, which reduces the density of states at the Fermi level and the Tc.

Amorphous Co–P alloys with compositions ranging between 18–25 at.% P were prepared by electrodeposition. Their magnetic properties were measured with a vibrating sample magnetometer between 4 and 520 °K in fields up to 8 kOe. The coercive force Hc and the ratio of remanence to saturation magnetization, σr / σs, of the alloys were several hundred times lower for the amorphous than for their as‐crystallized states. Earlier results indicating sharp increases in initial permeability with annealing, short of crystallization, were confirmed. The magnetic moment per atom, n, from low‐temperature measurements, decreases with increasing P content. In particular, the results at low P content indicate the transfer of four P valence electrons at the dilute limit, while those at >23 at.% P indicate a more rapid decrease of n than was expected from the rigid band model and suggest that n→0 at 32 at.% P. Both Tc and the spontaneous magnetization in the vicinity of Tc were determined by the method of thermodynamic parame...

Extended Huckel calculations are reported for clusters of Pd, Ag, Cu, Au, Pd−Ag, and Ni−Cu containing up to 55 atoms. Electronic properties important in catalysis are calculated and include the width and position of conduction−band states. Silver particles have a conduction band that shows increasing spread with increasing size. It is 5 eV wide at 55 atoms and the d states are 5 eV below the Fermi level. Palladium clusters have a high density of d states at the Fermi level, which is −7.9 eV for Pd19. Fewer d holes are present on surface than interior Pd atoms in Pd19. Clusters of Cu/Ni and Ag/Pd show d holes on the Group VIII metal atom for compositions up to and greater than 60% Ib metal, in contrast to the rigid band model prediction.

Optical properties of cosputtered thin‐film (1500 A) polycrystalline Au‐Cr alloys have been investigated in the energy range 0.2–6.1 eV. Cosputtering of Au and Cr has extended the solubility limits of Cr in Au from 20 to 48 at.%. The reflectance data were analyzed by the Kramers‐Kronig method and presented in terms of intraband, and interband contributions. The observed frequency dependence of the relaxation time is explained on the basis of a two carrier mode. The shift in the Fermi level with increasing Cr concentration is found to be closer to the prediction of the Friedel theory than the rigid band model. The character of critical points for the interband transitions has been identified.

Measurements of the normal spectral emissivity of Ta–W and Nb–Mo alloys are reported. The emissivities were measured at 2000°, 2200°, and 2400°K in the wavelength range 0.4 to 4 μm. The emissivities of the alloys generally lie between the values of the pure constituents. The temperature coefficient and the x‐point wavelength of Ta–W alloys change in a characteristic way. The measurements support the validity of the rigid band model.

The optical properties of β′ phase CoAl, CoGa, and NiGa were studied as functions of composition and photon energy in the spectral region from 0.7 to 6.3 eV. Similar investigations were conducted on NiAl between 0.7 and 2.0 eV. The specimens were prepared by a mechanical polishing technique that was shown, by the use of annealing studies, to produce surfaces from which reliable optical data could be taken. Measurements were made by the use of two polarimetric techniques on a reflectometer that was designed by the authors. The results of the optical measurements indicate that some of the investigated alloys show free electron behavior in the infrared, although the limited spectral region of investigation did not permit the authors to apply the Drude free electron theory to the data with confidence. The possible presence of hybridized plasma oscillations is indicated by structure in the loss function. The prominent optical absorption structure which is displayed by these materials in the visible and ultraviolet regions of the spectrum, and which indicates the presence of interband transitions, has been interpreted by the use of a simple rigid band model.

An experimental method for determining the densities of states in solids based on photoemission and optical measurements is described and illustrated with data from Cu and Ni. Densities of states for Cu, Ag, Ni, and Fe determined by this technique are presented. The Cu density of states is found to be in reasonable agreement with the band calculations of Burdick except for the appearance of a rather large peak in the experimentally determined density of states 6.2 eV below the Fermi surface. The Ni density of states is dominated by a strong maximum 4.5 eV below the Fermi level. This maximum is not predicted either by recent band calculations or by the rigid band model using the Cu density of states. Recent suggestions of Phillips and Mott concerning this are outlined.

A theoretical analysis of the solubility of interstitials in transition metal alloys is given. The change‐of‐system free energy as the interstitials are formed from the atomic state to the ionized state during the dissolving process is found to be dominated by the electronic interaction. This electronic interaction energy is characterized by the energy band structure, a rigid band model being used for the case of these bcc alloys. The minimum exhibited in the density‐of‐states curve, caused by the overlapping of subbands, gives rise to an unusual free energy change. Numerical calculations predict the interstitial solubilities in good agreement with Jones' experimental result. By comparing the solubilities of hydrogen and oxygen, oxygen should be singly ionized as an interstitial in these alloys.

The electronic heat capacity, magnetic and structural properties of the ternary YFe3−xNix system, with 0

The magnetic susceptibility χ of Cr–Os alloys containing 0.3, 0.6, 1.1, and 2.0 at.% Os has been measured as a function of temperature T between 4.2 and 600 K. The χ vs T curves exhibit a well defined knee at the Neel temperature TN. TN increases with Os content, in agreement with earlier determinations from electrical resistivity data. at the Neel temperature TN. TN increases with Os content, in agreenment with earlier determinations from electrical resistivity data. The rise of TN is consistent with expectations based on the rigid band model for these alloys. The measured susceptibility in the antiferromagnetic regime below TN is compared with that calculated using the two‐band model for chromium. Variation in the size of the electron jack and hole octahedron upon alloying is taken into account within the rigid band approximation. The impurity and phonon‐scattering contributions to the susceptibility have been included. Agreement between theory and experiment is good over most of the temperature range, although discrepancies are apparent at low temperatures.

High‐resolution measurements of magnetic susceptibility χ of dilute alloys of Pd1−a Rh a (a = 0.001, 0.075, 0.015, 0.03, and 0.07) and Pd1−a Ag a (a = 0.001, 0.005, 0.012, 0.023, and 0.025) are presented for temperatures from 4.2° to 300°K and for fields up to 55 kG. The general features show a broad maximum of χ(4.2°K) between 0.03 Rh and 0.07 Rh for Pd(Rh), then a rapid decrease in χ(4.2°K) to the value of χ for pure Pd, and a further decrease of χ with increasing Ag content. Small effects of Fe impurities are noted and briefly discussed. The very rapid variation of χ versus Rh content is consistent with earlier measurements. The maximum of χ(T), observed at about 80°K for pure Pd, moves toward 0°K as Rh content increases to 0.03, but the maximum in χ(T) is almost independent of increasing Ag content. The measured susceptibility and electronic specific heat are used to estimate the Stoner exchange enhancement in Pd and Pd0.95Rh0.05 and the results are in reasonable agreement with independent high‐field results discussed elsewhere. The relevance of recent high‐resolution band calculations is briefly discussed. Finally, for simplicity, a rigid band model and the χ(4.2°K) data for the Pd(Rh) and Pd(Ag) alloys are employed to construct the density of states versus energy for Pd.

The optical reflectance of chromium alloys with up to 10 at.% manganese or 50 at.% vanadium was measured at room temperature for photon energies from 0.475 to 2.24 eV. The Cr–Mn alloy system shows a very slight shift of the chromium absorption edge to higher photon energies, whereas the addition of vanadium shifts the absorption edge to lower photon energies. For the alloy with 10 at.% V, the edge disappears to values below the measured photon energy range. The direction of the shift of the absorption edge can be explained qualitatively in a rigid band model with transitions from the t2g band to the Fermi level. This model was previously proposed to explain optical reflection data of chromium‐iron alloys.

The behavior of the magnetic susceptibility and the electronic specific heat of alloys of Ir with the other nearly filled d‐band elements indicates that a rigid band model cannot be used to describe the behavior of the susceptibility. It appears that the large‐susceptibility enhancement in these metals in mainly due to large intra‐atomic interactions which, e.g., are large on Pt ions in pure Pt and remain large when a Pt ion is placed in Ir.

Low‐temperature specific heats were measured in the systems of borides Co2B–Ni2B and FeB–CoB, especially near cF, the critical composition for ferromagnetism. In the critical concentration range the linear term γT is largely increased and the specific heat curves reveal anomalies at low temperature. Except for this cF range, the γ values, in conformity with the magnetic moments, describe the filling up of a d band in a rigid band model.

Photoemission and optical studies of transition metals alloyed into noble metals enable us to distinguish between the rigid band model for these alloys and models such as that of the virtual bound state in which the local nature of the transition‐metal d state is retained. For the noble‐metal‐rich Cu–Ni and Ag–Mn alloys we have studied, the results are in agreement with the virtual bound state model. For both systems, no change is observed in the energy separation between the top of the noble‐metal d band and the Fermi level. With the addition of Ni to Cu, states are formed above the Cu d states which extend to the Fermi level. For 7–14% Mn in Ag the filled Mn d states do not extend to the Fermi level, rather they are separated from it by about 1.5 eV. The width at half‐maximum of the virtual bound states is estimated to be about 1.5 eV for Ni in Cu and about 2 eV for Mn in Ag.