Point defects and p-type conductivity in Zn1-xMnxGeAs2

Positron annihilation spectroscopy is used to study point defects in Zn1–xMnxGeAs2 crystals with low Mn content 0≤x≤0.042 with disordered zincblende and chalcopyrite structure. The role of negatively charged vacancies and non-open-volume defects is discussed with respect to the high p-type conductivity with carrier concentration 10exp19≤p≤10exp21cm−3 in our samples. Neutral As vacancies, together with negatively charged Zn vacancies and non-open-volume defects with concentrations around 10exp16−10exp18 cm−3, are observed to increase with increasing Mn content in the alloy. The observed concentrations of defects are not sufficient to be responsible for the strong p-type conductivity of our crystals. Therefore, we suggest that other types of defects, such as extended defects, have a strong influence on the conductivity of Zn1–xMnxGeAs2 crystals.Peer reviewe

Native vacancy defects in Zn1-x(Mn,Co)xGeAs2 studied with positron annihilation spectroscopy

We have studied vacancy defects in chalcopyrite semimagnetic semiconducting mixed Zn1−x(Mn,Co)xGeAs2 bulk crystals with alloy composition x varying between 0.052 to 0.182 using positron annihilation spectroscopy. We identified As vacancies, potentially complexed with the transition metal alloying elements, in all the studied samples, while no cation vacancy related defects were detected. The positron lifetimes for the bulk ZnGeAs2 lattice and neutral As vacancy were determined to be τB=220–230 ps and τAs=300±10 ps, respectively. Our results also show that the p-type conductivity in the samples is not due to cation vacancy related acceptor centers. The As vacancies were found to be present at such low concentrations that they cannot be responsible for the compensation of the p-type conductivity or the reduction of mobility in the Zn1−x(Mn,Co)xGeAs2 samples.Peer reviewe

Unconventional ferromagnetism and transport properties of (In,Mn)Sb dilute magnetic semiconductor

Narrow-gap higher mobility semiconducting alloys In_{1-x}Mn_{x}Sb were synthesized in polycrystalline form and their magnetic and transport properties have been investigated. Ferromagnetic response in In_{0.98}Mn_{0.02}Sb was detected by the observation of clear hysteresis loops up to room temperature in direct magnetization measurements. An unconventional (reentrant) magnetization versus temperature behavior has been found. We explained the observed peculiarities within the frameworks of recent models which suggest that a strong temperature dependence of the carrier density is a crucial parameter determining carrier-mediated ferromagnetism of (III,Mn)V semiconductors. The correlation between magnetic states and transport properties of the sample has been discussed. The contact spectroscopy method is used to investigate a band structure of (InMn)Sb near the Fermi level. Measurements of the degree of charge current spin polarization have been carried out using the point contact Andreev reflection (AR) spectroscopy. The AR data are analyzed by introducing a quasiparticle spectrum broadening, which is likely to be related to magnetic scattering in the contact. The AR spectroscopy data argued that at low temperature the sample is decomposed on metallic ferromagnetic clusters with relatively high spin polarization of charge carriers (up to 65% at 4.2K) within a cluster.Comment: 19 pages, 9 figures, 1 tabl

Automated detection of buildings on aero images

One of the challenging problems in photogrammetry is extracting of three-dimensional objects from aero images, in particular, extraction of different kinds of buildings. All methods that provide satisfactory results are rather time consuming and process data quite long. In the paper we propose a method that detects areas on aero images that might contain a building behind them. Our method allows reducing the amount of data which should be processed by more complex algorithms. This leads to reducing of the total time spent on extraction process

Magnetic Behavior of Carboxylate and β-Diketonate Lanthanide Complexes Containing Stable Organometallic Moieties in the Core-Forming Ligand

Information concerning the structures of compounds of rare earth elements with carboxylic acids and a β-diketone containing stable organometallic moieties that we obtained previously is presented. Additional results for 15 complexes with the [Gd2O2] core allowed confirming and improving the correlation between JGd–Gd′ and the Gd…Gd distance for complexes of this type that we found earlier. For the first time, dc and ac magnetic measurements were carried out for the formerly-described complex [Dy2(O2CCym)4(NO3)2(DMSO)4] (2), Cym = (η5-C5H4)Mn(CO)3), and two new binuclear complexes, namely [Dy2(O2CFc)4(NO3)2(DMSO)4] (3), and [Dy2(O2CFc)6(DMSO)2(H2O)2] (4), Fc = (η5-C5H4)Fe(η5-C5H5)). For binuclear [Dy2(O2CCym)6(DMSO)4] (1), as well as for a 1D-polymer [Dy(O2CCym)(acac)2(H2O)]n (6), ac magnetic measurements were carried out more precisely. The characteristics of a single-molecule magnet and of a single-chain magnet were determined for Complexes 2 and 6, respectively

X-ray photoelectron spectra of heterometallic 3d-metal carboxylate complexes

The electronic structure and magnetic states in the heterometallic hexanuclear complex Mn 4 II Fe 2 III (μ4-O)2(Piv)10 • MeCN4 have been studied by X-ray photoelectron spectroscopy (XPS). The substitution of two Mn atoms for two Fe atoms in the hexanuclear complex was found to have an effect on the patterns of iron and manganese X-ray photoelectron spectra. XPS data are evidence of the high-spin paramagnetic state of MnII and FeIII atoms, as well as of the ligand-metal charge transfer upon complex formation. In the heteroatomic complex, the degree of bond covalence increased for both the manganese and iron atoms. The results obtained are in good agreement with X-ray diffraction data. © 2011 Pleiades Publishing, Ltd