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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.

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]

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]

La0.67Ca0.33MnO3 (LCMO) nanoparticles were prepared by the sol–gel method. The composite samples of (LCMO)x/(ZrO2)1-x were obtained by mixed LCMO and ZrO2 powders and sintered at 1300°C. Detailed studies of magnetic and magnetotransport properties for composite samples have been performed. The x-ray diffraction and scanning electronic microscopy observations indicated that no reaction happened between LCMO and ZrO2 grains. The low-field magnetoresistance (LFMR) can be greatly improved by ZrO2 addition close to the percolation threshold of x=60%. The field sensitivity of MR at 77 K in the low field region for (LCMO)0.4/(ZrO2)0.6 is 7%/100 Oe, which is one order of magnitude larger than that obtained by pure LCMO. The enhancement of the spin-dependent tunnelling and scattering of electrons at the interfaces of LCMO and ZrO2 grains is responsible for the enhanced LFMR. [ABSTRACT FROM AUTHOR]

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]

The effects of Ag addition in Ti-doped La0.67Ba0.33MnO3 (LBT) (abbreviated as LBT/Agx, where x is the nominal molar ratio of Ag) on the electric and magnetoresistance (MR) properties have been studied systematically. The results show that the resistivity of the samples decreases dramatically with increasing Ag addition and reaches its minimum for x = 0.27. The room-temperature MR ratio of LBT/Agx increases with increasing x and reaches its maximum at x = 0.27. The MR ratio at 280 K for the x = 0.27 sample at H = 10 kOe is as large as 41%, which is about 3.4 times larger than that for LBT. The Ag addition makes the LBT crystallites more perfect and uniform, and suppresses the magnetic scattering at the grain boundaries. The Ag conduction channels penetrating into the insulating regions can also lower the resistivity. The near room-temperature TC and low resistivity of the Ag-added LBT are responsible for the large intrinsic room-temperature MR. [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]