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Magnetotransport measurements were performed on a series of nanostructured Bi1-xSbx alloy samples with an Sb content in the range between 0% and 60%. The samples were prepared by cold pressing and annealing of crystalline Bi1-xSbx nanoparticles, which were synthesized by mechanical alloying. The incorporation of Sb changes the band structure of these nanotextured alloys as well as their transport behavior. With increasing Sb content the band gap increases and reaches a maximum band gap of 42 meV at an Sb concentration of about 14% determined from temperature dependent resistivity measurements. For even higher Sb content, the band gap decreases again. The bands and thus the band gaps are shifted with respect to bulk material due to quantum confinement effects in the nanostructures. The change of the band structure with varying Sb content strongly affects the magnetoresistance behavior as well as the magnetic field dependence of the Hall-coefficient. Using a three band model in order to describe both properties, it was possible to determine the main band parameters of the nanostructured material as a function of the Sb content. [ABSTRACT FROM AUTHOR]

Random arrangements of ferromagnetic MnAs nanoclusters were deposited on (111)B-GaInAs surfaces by standard metal-organic vapor-phase epitaxy (MOVPE). Ordered arrangements of MnAs nanoclusters and cluster chains were obtained by selective-area MOVPE on prepatterned (111)B-GaAs substrates. This new method enables one to control the arrangement of nanoclusters in the growth process offering interesting opportunities to tune the properties of individual MnAs clusters as well as the interaction between the carriers in the surrounding semiconductor matrix and the clusters. The magnetic anisotropy of the MnAs clusters was investigated by magnetic force microscopy and ferromagnetic resonance measurements. The in-plane magnetic anisotropy is mainly determined by the interplay of cluster shape and magnetocrystalline anisotropy while the hard magnetic axis of the clusters is perpendicular to the sample plane independent of cluster shape. The magnetotransport measurements demonstrate that the cluster arrangements strongly influence the transport properties. [ABSTRACT FROM AUTHOR]

The angle-dependent behavior of the magneto-resistance of a series of low-temperature molecular beam epitaxy grown Ga0.98Mn0.02As samples on (311)A-GaAs-substrates is studied. The samples are annealed at different temperatures in a range from 300 °C to 500 °C, which leads to a redistribution of the manganese in the sample and finally to the formation of MnAs clusters. As a consequence, the angle-dependence of the magneto-resistance changes with increasing annealing temperature and vanishes finally at an annealing temperature of 400 °C. The observed anisotropy of the magneto-resistance can be correlated with the magnetic anisotropy of the magnetization. The parameters describing this magnetic anisotropy and their changes due to annealing are extracted from the experimental magneto-resistance data by a fitting procedure. The magnetocrystalline anisotropy of the samples can be described by the sum of cubic and uniaxial contributions. The former are not affected by the annealing whereas the latter change considerably. [ABSTRACT FROM AUTHOR]

We study the changes of magnetoresistance induced by controlled thermal annealing at temperatures ranging from 300 to 600 °C of a Ga0.98Mn0.02As alloy grown by low-temperature molecular beam epitaxy. We use a resistor-network model for describing the electrical transport as a function of temperature and external magnetic field. The model is founded on classical semiconductor band transport and neglects many-body interactions. The peculiarities of dilute magnetic semiconductors, in particular, the magnetic-field induced changes of the density of states and the potential fluctuations due to the giant Zeeman splitting in the paramagnetic phase as well as spontaneous magnetization effects in the ferromagnetic phase, are accounted for in a mean-field fashion. This empirical transport model based on reasonable assumptions and realistic material parameters yields a satisfactory quantitative description of the experimentally obtained temperature and magnetic-field dependence of the resistivity of the entire series of annealed Ga0.98Mn0.02As samples, which exhibit metallic, semiconducting, and almost insulating transport behavior with increasing annealing temperature. Our analysis provides further understanding of the annealing-induced changes of the transport properties in dilute magnetic III-Mn-V semiconductors. [ABSTRACT FROM AUTHOR]

We report on magnetotransport measurements on a MnAs nanocluster arrangement consisting of two elongated single-domain clusters connected by a metal spacer. The arrangement was grown on GaAs(111)B-substrates by selective-area metal organic vapor phase epitaxy. Its structural properties were investigated using scanning-electron microscopy and atomic-force microscopy, while its magnetic domain structure was analyzed by magnetic-force microscopy. The magnetoresistance of the arrangement was investigated at 120?K for two measurement geometries with the magnetic field oriented in the sample plane. For both geometries, discrete jumps of the magnetoresistance of the MnAs nanocluster arrangement were observed. These jumps can be explained by magnetic-field induced switching of the relative orientation of the magnetizations of the two clusters which affects the spin-dependent scattering in the interface region between the clusters. For a magnetic field orientation parallel to the nanoclusters' elongation direction a spin-valve like behavior was observed, showing that ferromagnetic nanoclusters may be suitable building blocks for planar magnetoelectronic devices. [ABSTRACT FROM AUTHOR]

We study the transport properties of artificially structured n-type ZnO:Al thin films prepared by rf magnetron sputtering on glass substrates. The samples were patterned with an array of 4×4 and 8×8 μm2 holes. With decreasing hole size, the resistance of the samples increases. Filling the holes with Au or Al increases and decreases the resistance, respectively. All samples show a negative magnetoresistance, which becomes more pronounced with decreasing hole diameter. The filling of the holes with Au or Al reduces the effects of the artificial structuring on the magnetoresistance. [ABSTRACT FROM AUTHOR]

The magnetoresistance properties of GaAs:Mn/MnAs granular hybrid structures consisting of ferromagnetic MnAs clusters within a paramagnetic GaAs:Mn host differ considerably from those of paramagnetic and ferromagnetic (Ga,Mn)As alloys. We analyze the magnetoresistance effects on the basis of a resistor network model. Typical experimental findings are reproduced and their dependence on cluster density and random spatial arrangement of the clusters are revealed. Controlled spatial positioning of the MnAs clusters within the GaAs:Mn host offers interesting opportunities for optimizing the magnetoresistance properties for applications and for overcoming problems of miniaturization arising from cluster statistics. [ABSTRACT FROM AUTHOR]