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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]

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]

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]