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Abstract: TiO2/Co thin films were prepared on glass substrates under thermal non-equilibrium condition by alternately sputtering very thin TiO2 and Co layers for 60 periods. Microstructure and composition analyses by X-ray diffraction, transmission electron microscopy, X-ray photoemission spectroscopy and electron energy-loss spectroscopy indicated that the Co element was incorporated into TiO2 to form the Ti1− x Co x O2 magnetic semiconductors. The obvious Kerr rotations in the samples were observed, and the relation between the Kerr rotation and Co concentration was discussed. [Copyright &y& Elsevier]

Abstract: The resonant modes in a quantum well (QW) structure composed of three slabs of two dimensional (2D) photonic crystals with different lattice constants are analyzed with plane-wave-based transfer matrix method (TMM). It is found that the energy band of the well slab submerged into the band gap of barrier slab is discretized into quantized modes and the number of the resonant modes changes with the well slab thickness. A model structure of asymmetrical photonic QW consisting of two slabs of 2D photonic crystals with different lattice constants and one uniform dielectric slab in between is proposed and the resonant modes in it are investigated with the same method. A useful numerical simulation method for theoretical discussion as well as for practical application about photonic QW structure of photonic crystals with different lattice constants is proposed. [Copyright &y& Elsevier]

Homogeneous amorphous MnxGe1-x:H films were synthesized under thermal nonequilibrium condition by magnetron co-sputtering technology with hydrogen in Ar atmosphere. Compared to the MnxGe1-x films without hydrogen, the MnxGe1-x:H films with hydrogen show higher concentration of hole carriers, larger conductivity, and higher saturation magnetization. Moreover, it was found that the anomalous Hall resistivity is proportional to the perpendicular magnetization. These electrical and magnetic properties indicate that the ferromagnetism of the MnxGe1-x:H films is intrinsic ferromagnetism mediated by the spin-polarized hole carriers. [ABSTRACT FROM AUTHOR]

We theoretically investigated the electronic structures and magnetic properties of (Mn,C)-codoped ZnO system based on the first-principles calculations within a GGA+Up,d approach. We found that codoping C is a promising approach to enhance the ferromagnetic coupling between the nearest-neighboring Mn ions due to the strong hybridization between the C:2p and the Mn:3d states. Moreover, the spin-polarized states induced by C are so extended that they can mediate long-ranged ferromagnetic exchange interactions beyond the nearest-neighboring case. Therefore, (Mn,C)-codoped ZnO is expected to be a ferromagnetic semiconductor with long-ranged ferromagnetism and high Curie temperature. [ABSTRACT FROM AUTHOR]

Amorphous Ge1-xMnx magnetic semiconductor films with high Mn concentrations were prepared on liquid-nitrogen (LN2)-cooled glass substrates by ultrahigh vacuum thermal coevaporation. Hysteresis loops measured at 5 K show coexistence of ferromagnetism and paramagnetism. The maximum Curie temperature of 220 K was found in Ge0.48Mn0.52 film. Moreover, exchange bias occurs in magnetization hysteresis loops for samples with higher Mn concentrations, which can be explained by the antiferromagntic exchange coupling between ferromagnetic phase and antiferromagnetic phase. All the Ge1-xMnx magnetic semiconductor films show semiconducting transport behavior and anomalous Hall effects below the Curie temperature, indicating carrier-mediated ferromagnetism. [ABSTRACT FROM AUTHOR]

The effect of atomic disorder or chain length on the stability of photoinduced polarization inversion has been studied. The atomic disorder was simulated by square-random or Gaussian-random model. It was found that for the square-random distribution case, photoinduced polarization inversion remains steadily when atomic disorder is less than [FRACTION SHAPE="CASE"][NUM]1[/NUM][DEN]8[/DEN][/FRACTION]a (a is the lattice constant of polyacetylene), the reversion polarization disappears and gets into normal polarized state when the disorder is stronger than over [FRACTION SHAPE="CASE"][NUM]1[/NUM][DEN]8[/DEN][/FRACTION]a. The reason of a normal polarization resulted from the strong lattice disorder was discussed. The relationship between the reverse polarization of biexciton state and the confinement constant t[sub e] as well as the variation of chain length was also studied. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which prepared cobalt-niobium/palladium multilayers by radio frequency sputtering method. Experimental details; Results of low-angle x-ray diffraction; Conclusion.

The magnetic and magneto-transport properties of amorphous CoO 1− v films have been systematically studied and manipulated by changing the concentration of oxygen vacancies. A giant exchange bias field H E ≈4380 Oe and a large coercivity H C ≈8500 Oe are observed at 5 K for the composite films. And, a metal to insulator transition has been demonstrated in CoO 1− v films by decreasing the concentration of oxygen vacancies. Moreover, a remarkable decrease of the exchange bias and a slight increase of the saturation magnetization can be obtained by modifying the microstructures through post-thermal annealing. [ABSTRACT FROM AUTHOR]

Amorphous MnxGe1-x: H ferromagnetic semiconductor films prepared in mixed Ar with 20% H2 by magnetron co-sputtering show global ferromagnetism with positive coercivity at low temperatures. With increasing temperature, the coercivity of MnxGe1-x:H films first changes from positive to negative, and then back to positive again, which was not found in the corresponding MnxGe1-x and other ferromagnetic semiconductors before. For Mn0.4Ge0.6:H film, the inverted Hall loop is also observed at 30 K, which is consistent with the negative coercivity. The negative coercivity is explained by the antiferromagnetic exchange coupling between the H-rich ferromagnetic regions separated by the H-poor non-ferromagnetic spacers. Hydrogenation is a useful method to tune the magnetic properties of MnxGe1-x films for the application in spintronics. [ABSTRACT FROM AUTHOR]

A series of high quality single crystalline epitaxial Zn0.95Co0.05O thin films is prepared by molecular beam epitaxy. Superparamagnetism and ferromagnetism are observed when the donor density is manipulated in a range of 1018 cm-3- 1020 cm-3 by changing the oxygen partial pressure during film growth. The conduction shows variable range hopping at low temperature and thermal activation conduction at high temperature. The ferromagnetism can be maintained up to room temperature. However, the anomalous Hall effect is observed only at low temperature and disappears above 160 K. This phenomenon can be attributed to the local ferromagnetism and the decreased optimal hopping distance at high temperatures. [ABSTRACT FROM AUTHOR]

ZnO thin film growth prefers different orientations on the etched and unetched SrTiO3(STO)(110) substrates. Inclined ZnO and cobalt-doped ZnO (ZnCoO) thin films are grown on unetched STO(110) substrates using oxygen plasma assisted molecular beam epitaxy, with the c-axis 42° inclined from the normal STO(110) surface. The growth geometries are ZnCoO[100]//STO[11¯0] and ZnCoO[11¯1]//STO[001]. The low temperature photoluminescence spectra of the inclined ZnO and ZnCoO films are dominated by D0X emissions associated with A0X emissions, and the characteristic emissions for the 2E(2G)→4A2(4F) transition of Co2+ dopants and the relevant phonon-participated emissions are observed in the ZnCoO film, indicating the incorporation of Co2+ ions at the lattice positions of the Zn2+ ions. The c-axis inclined ZnCoO film shows ferromagnetic properties at room temperature. [ABSTRACT FROM AUTHOR]

First-principles calculations of undoped HfO and cobalt-doped HfO have been carried out to study the magnetic properties of the dielectric material. In contrast to previous reports, it was found that the native defects in HfO could not induce strong ferromagnetism. However, the cobalt substituting hafnium is the most stable defect under oxidation condition, and the ferromagnetic (FM) coupling between the cobalt substitutions is favorable in various configurations. We found that the FM coupling is mediated by the threefold-coordinated oxygen atoms in monoclinic HfO and could be further enhanced in electron-rich condition. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011 [ABSTRACT FROM AUTHOR]

We propose a defect-complex model to clarify the origin of ferromagnetism in Co-doped ZnO magnetic semiconductors, based on first-principles calculations. The spin-polarized defect states of oxygen vacancy (VO) induced by the charge-transfer process are essential to the ferromagnetism. Depending on the charge state of VO and carrier concentration, (VO 2+ +zinc interstitial) and (VO 0 +zinc vacancy) defect complexes are predicted to control the ferromagnetic exchange interaction between the Co ions for insulating and conductive samples, respectively. [ABSTRACT FROM AUTHOR]

Abstract: We performed first-principles calculations to investigate the electronic structures and magnetic properties of neutral and charged intrinsic defects of wurtzite ZnO. Our results show that an isolated single charged Zn vacancy can introduce a magnetic moment of , and may be responsible for the unexpected ferromagnetism in the system. [ABSTRACT FROM AUTHOR]

Abstract: A novel approach was developed to calculate temperature-dependent Seebeck coefficient of heavily doped systems. The electronic density of states (DOS) and Fermi energy were determined and then, using these two parameters, the Seebeck coefficient was calculated by using Boltzmann transport theory. This approach is applied to heavily La-doped SrTiO3. The calculated Seebeck coefficient agrees well with the experimental data. By analyzing the results, it was shown that Seebeck coefficient is greatly affected by the asymmetry of DOS with respect to Fermi energy. [Copyright &y& Elsevier]

Abstract: Amorphous GaN (a-GaN) films on Si (111) substrates have been deposited by RF magnetron sputtering with GaN powder target. The growth process from amorphous GaN to polycrystalline GaN is studied by XRD, SEM, PL and Raman. XRD data mean that annealing under flowing ammonia at 850–950°C for 10min converts a-GaN into polycrystalline GaN (p-GaN). The growth mechanism can be mostly reaction process through N3− in amorphous GaN replaced by N3− of NH3. Annealing at 1000°C, the appearance of GaN nanowires can be understood based on the vapor–liquid–solid (VLS) mechanism. In addition, XRD, PL and Raman measurement results indicate that the quality of GaN films increases with increasing temperature. The tensile stress in the films obtained at 1000°C is attributable to the expansion mismatch between GaN and Si, with the gallium in the film playing a negligible role. [Copyright &y& Elsevier]

Abstract: TiO2:Co thin films of high Co concentration were investigated by the high resolution transmission electron microscopy, physical property measurement system and energy dispersive X-ray. The as-deposited films are amorphous magnetic semiconductors and we did not find any Co metal particles in them. The electronic transport process in the low-temperature range below 80K could be described by the spin-dependent variable-range-hopping process. However, after the samples were annealed at 300°C, large amounts of Co metal particles were observed to connect each other and the films show a metallic behavior. The origin of ferromagnetism of the thin films is also discussed. [Copyright &y& Elsevier]

Abstract: Structural, magnetic, electrical, and magnetotransport properties have been carried out on the Ag-added La0.67Ba0.33MnO3/(TiO2)0.035 (LBT) (abbreviated by LBT/Ag x ,) composites. Ag addition has little influence on the magnetization or Curie temperature (T C), but decreases the resistivity (ρ) and sharps the ρ peak evidently. The ρ in the ferromagnetic (FM) metallic regime is proportional to T 2, reflecting that the conductive mechanism mainly arises from the electron–electron scattering. In the paramagnetic (PM) insulating region, the ρ data fit well to the self-trapped small polaron hopping model. The ρ–T curves for x =0.27 and 0.30 samples fit well with the phenomenological percolation approach, which is based on the phases segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. These excellent agreements highlight the dominant intrinsic behavior of LBT. In addition, from the magnetotransport measurements, a large magnetoresistance (MR) ratio up to 41% was obtained at 280K, and 10kOe for x =0.27 sample. The good fits between the field dependence of MR and Brillouin function indicate that the MR behavior in the Ag-added LBT is induced by the spin-dependent hopping of the electrons among the spin clusters, and which is related to the increase and growth of the FM spin clusters. [Copyright &y& Elsevier]

Abstract: We have prepared a series of polycrystalline manganites with the nominal compositions, La0.67Ba0.33Mn0.88Cr0.12O3/Ag x (LBMCO/Ag x ) (x is the mole fraction) with , 0.05, 0.1, 0.15, 0.2, 0.23, 0.27, 0.3, 0.35. The X-ray diffraction patterns show that the samples with are two-phase composites. The Ag addition in LBMCO improves the properties of grain surfaces/boundaries and reduces the resistivity of the composites. For sample, a minimum resistivity is obtained and a maximum room temperature magnetoresistance up to −54.5% was observed at 288K, 1T field. The room temperature T C and the reduced resistivity are responsible for the enhancement of room temperature MR. [Copyright &y& Elsevier]

Abstract: The giant magnetoimpedance (GMI) effects in radio frequency sputtered FeCuNbSiB films with a dc magnetic field applied in the process of deposition are presented, and the relation between annealing temperature and GMI ratio is investigated. The results show that 300 °C is the optimum annealing temperature, at which the GMI ratios reach the maximum values of about 38% and 27% in longitudinal and transverse dc magnetic fields, respectively, at a frequency of 13 MHz. The longitudinal magnetic responses of GMI ratios show very sharp peaks around the transverse anisotropy field, and the sensitivity can reach a value larger than 47.5%/kA/m in the field range 0.4∼6 kA/m, at 13 MHz. The frequency dependencies of the magnetoresistance and magnetoreactance indicate that at lower frequencies, the giant magnetoinductance effect is dominant, while at higher frequencies, skin effect becomes important, and the GMI effect is determined by the change of both the resistance and reactance components. [Copyright &y& Elsevier]

Abstract: The electrical and magnetoresistant properties of La0.67(Ca0.65Ba0.35)0.33MnO3/Ag x (abbreviated by LCBMO/Ag x ) have been studied. The results show that Ag addition causes a decrease of resistivity dramatically and especially induces a large enhancement of room temperature magnetoresistance (MR). The room temperature MR ratio for x=0.27 sample in 10kOe magnetic field is 41%, almost 20 times larger than that for x=0 sample. This enhancement is related to that the Curie temperature (T c) of the sample is near room temperature, as well as the significant reduction of resistivity. The good fits of experimental results for x=0.27 sample to Brillouin function indicate that the MR behavior in the Ag added LCBMO is induced by the spin-dependent hopping of the electrons between the spin clusters, which is an intrinsic property of the CMR materials. [Copyright &y& Elsevier]

Abstract: Lattice vibration in one-dimensional copolymer chains was studied in the framework of a tight-binding model including the interfacial coupling between homopolymer segments. The vibration density of states was obtained numerically and the characteristic of the vibration modes was recognized. It was found that there exist two types of modes, confined and hybridized. Interface modes might appear at a strong interfacial interaction. The characteristic of the organic quantum well or superlattice of a copolymer chain was discussed from the point of the lattice vibration. [Copyright &y& Elsevier]

Enhancements of the low-field (LFMR) and high-field magnetoresistance (HFMR) were observed in the manganite system prepared by doping Nb2O5 into La0.67Sr0.33MnO3 powders. The maximum MR ratios at 77 K with H=1 T and 1 kOe are 30% and 20% for the 0.07 molar ratio doped sample, which are 1.7 times and 1.6 times as large as that for LSMO, respectively. An MR effect up to 6.5% was also found for the sample with x=0.03 at room temperature (RT). The spin-dependent tunneling and scattering at the interfaces of grain boundaries are responsible for the LFMR while the HFMR originates from a noncollinear spin structure in the surface layer. With increasing x, the Curie temperature (TC) decreases monotonically from 364 to 154 K while the temperature TP related to the peak resistivity decreases firstly to a minimum of 204 K (x=0.06) and then rises up to 240 K (x=0.1). There is a maximum resistivity ρ for the sample with x=0.06, which is higher than that for LSMO by five orders of magnitude. It is due to the enhancement of spin-dependent and independent scattering and tunneling effects on the interfaces of grain boundaries and inside the grains. [Copyright &y& Elsevier]

La0.67Ca0.33MnO3 (LCMO) fine powder was prepared by a sol–gel procedure. The effects of Ti addition in LCMO on the magnetic, transport and magnetoresistive (MR) properties have been studied systematically. With increasing Ti addition, the magnetization and Curie temperature for the samples decrease monotonously, and the resistivity increases dramatically. The MR effect increases first and then decreases after a maximum MR ratio is reached. When the amount of Ti addition is 5.5% (molar ratio), a maximum MR ratio as large as 500% in 10 kOe at 120 K was obtained, which is 25 times larger than that obtained by the undoped LCMO. The effect of Ti addition is to introduce local magnetic inhomogeneity and inducing spin clusters in the material. Fitting the experimental results to the Brillouin function proposed by Wagner et al. indicates that a possible explanation for the MR behaviour in the Ti-doped LCMO is the formation of spin clusters. [Copyright &y& Elsevier]

The dynamics of a bipolaron in a phenylene ring polymer in the presence of a high electric field was studied by using an extended tight-binding model. Due to the strong electron–phonon coupling, the doped electrons cannot dissociate from the lattice even if the applied electric field is as high as up to 5×106 V/cm. The lattice potential energy and the electronic energy oscillate out of phase. [Copyright &y& Elsevier]

Polaron tunneling is studied in xPA/nPPP/xPA (polyacetylene (PA), poly(p-phenylene) (PPP)) triblock copolymer, which has a well–barrier–well structure. The chain is modeled by a modified tight-binding Hamiltonian with an external electric field. It is found that there exists a threshold value of the external field for the polaron to tunnel through the middle barrier. The critical tunneling electric field mainly depends upon the length of the PPP segment. [Copyright &y& Elsevier]

Magnetoresistance and rectification are two fundamental physical properties of heterojunctions and respectively have wide applications in spintronics devices. Being different from the well known various magnetoresistance effects, here we report a brand new large magnetoresistance that can be regarded as rectification magnetoresistance: the application of a pure small sinusoidal alternating-current to the nonmagnetic Al/Ge Schottky heterojunctions can generate a significant direct-current voltage, and this rectification voltage strongly varies with the external magnetic field. We find that the rectification magnetoresistance in Al/Ge Schottky heterojunctions is as large as 250% at room temperature, which is greatly enhanced as compared with the conventional magnetoresistance of 70%. The findings of rectification magnetoresistance open the way to the new nonmagnetic Ge-based spintronics devices of large rectification magnetoresistance at ambient temperature under the alternating-current due to the simultaneous implementation of the rectification and magnetoresistance in the same devices. [ABSTRACT FROM AUTHOR]

Co2MnSi thin films are made by magnetron sputtering onto MgO (001) substrates. The crystalline quality is improved by increasing depositing temperature and/or annealing temperature. The sample deposited at 550°C and subsequently annealed at 550°C (sample I) exhibits a pseudo-epitaxial growth with partially ordered L21 phase. Sample I shows a four-fold magnetic anisotropy, in addition to a relatively weak uniaxial anisotropy. The Gilbert damping factor of sample I is smaller than 0.001, much smaller than reported ones. The possible reasons responsible for the small Gilbert damping factor are discussed, including weak spin-orbit coupling, small density of states at Fermi level, and so on. [ABSTRACT FROM AUTHOR]

The thermoelectric properties of Sr0.61Ba0.39Nb2O6−δ ceramics, reduced in different conditions, are investigated in the temperature range from 323 K to 1073 K. The electrical transport behaviors of the samples are dominated by the thermal-activated polaron hopping in the low temperature range, the Fermi glass behavior in the middle temperature range, and the Anderson localized behavior in the high temperature range. The thermal conductivity presents a plateau at high-temperatures, indicating a glass-like thermal conduction behavior. Both the thermoelectric power factor and the thermal conductivity increase with the increase of the degree of oxygen-reduction. Taking these two factors into account, the oxygen-reduction can still contribute to promoting the thermoelectric figure of merit. The highest ZT value is obtained to be ∼0.19 at 1073 K in the heaviest oxygen reduced sample. [ABSTRACT FROM AUTHOR]

The first-principles calculations are employed to investigate the electrical properties of polar MgO/BaTiO3 (110) interfaces. Both n-type and p-type polar interfaces show a two-dimensional metallic behavior. For the n-type polar interface, the interface Ti 3d electrons are the origin of the metallic and magnetic properties. Varying the thickness of BaTiO3 may induce an insulator–metal transition, and the critical thickness is 4 unit cells. For the p-type polar interface, holes preferentially occupy the interface O 2py state, resulting in a conducting interface. The unbalance of the spin splitting of the O 2p states in the interface MgO layer leads to a magnetic moment of about 0.25μB per O atom at the interface. These results further demonstrate that other polar interfaces, besides LaAlO3/SrTiO3, can show a two-dimensional metallic behavior. It is helpful to fully understand the role of polar discontinuity on the properties of the interface, which widens the field of polar-nonpolar interfaces. [ABSTRACT FROM AUTHOR]