Search

The resistivity ρ, magnetoresistance Δρxx/ρ0(P), and Hall coefficient RH are measured in a (Cd1 ‒ xZnx)3As2 sample with х = 0.31 under the action of uniform pressure and at various temperatures in the range 80–400 K. These samples are obtained by the modified Bridgman method. The composition of the samples and their homogeneity are controlled by X-ray phase analysis and energy-dispersive X-ray spectroscopy. The results of energy dispersive X-ray spectroscopy show that the distribution of elements in the sample is uniform. It is found that the resistivity increases with increasing temperature, and the change in ρ(T) has a metallic character. The Hall coefficient RH in the field decreases slightly with increasing temperature and retains a negative sign throughout the entire range under study. With increasing pressure, anomalies are observed in the baric dependences of the electrical resistivity ρ(Р), magnetoresistance Δρxx/ρ0(Р), and the Hall coefficient RH(Р). Increasing the uniform pressure leads to suppression of the positive magnetoresistance. In the phase-transition region, the negative magnetoresistance at a pressure of Р (2.4–2.7) GPa in a field of 5 kOe is a maximum value of 1.7. [ABSTRACT FROM AUTHOR]

Příspěvek se zabývá hledáním faktorů, které ovlivňují dosažení kladného nebo záporného hospodářského výsledku hlubinných uhelných dolů Ukrajiny. Je použitá metoda diskriminační analýzy. Dochází se k závěru, že nejvýznamnější příčinou jsou důlně-geologické podmínky, v menší míře pak vliv lidského činitele.

Článek analyzuje faktory ovlivňující trh s uhlím na Ukrajině. Na základě této analýzy jsou formulovány podmínky dalšího rozvoje uhelného průmyslu Ukrajiny.

Single crystals of a diluted magnetic semiconductor (Cd1-x-yZnxMny)3As2 (CZMA) (x + y = 0.4;y=0.04 and 0.08) obtained by Bridgman method were used. The Shubnikov-de Haas (SdH) effect was observed within studying of the dependence of the resistivity on the magnetic field in CZMA solid solutions. The values of the cyclotron mass mc, Hall and Shubnikov carrier concentrations were calculated.

Structural and magnetic properties of the group III-V diluted magnetic semiconductor In1-xMnxSb with x = 0.005-0.06, including the nuclear magnetic resonance (NMR) investigations, are reported. Polycrystalline In1-xMnxSb samples were prepared by direct alloying of indium antimonide, manganese and antimony, followed by a fast cooling of the melt with a rate of 10-12 K/s. According to the X-ray diffraction data, part of Mn is substituted for In, forming the In1-xMnxSb matrix. Atomic force microscopy and scanning tunneling microscopy investigations provide evidence for the presence of microcrystalline MnSb inclusions (precipitates), having a size of ∼100-600 nm, and the fine structure of nanosize grains with a Gaussian distribution around the diameter of ∼24 nm. According to the NMR spectra, the majority of Mn enters the MnSb inclusions. In addition to the single Mn ions, which contribute to the magnetization M (T) only in the low-temperature limit of T < 10-20 K, and MnSb nanoprecipitates responsible for the ferromagnetic (FM) properties of In1-xMnxSb, a superparamagnetic (SP) contribution of atomic-size magnetic Mn complexes (presumably dimers) has been established. The fraction of the MnSb phase, η ∼ 1-4%, as well as the concentration, nsp ∼ (0.8-3.2) × 1019 cm-3, and the magnetic moment of the Mn dimers, μ ∼ 8-9 μB, are determined. The solubility limit of Mn in the InSb matrix, NSL ∼ 1020 cm-3, is estimated. Hysteresis in low (H < 500 Oe) magnetic fields and saturation of the magnetization in high (H > 20 kOe) magnetic fields are observed, indicating a presence of the SP and FM contributions to the dependence of M (H) up to T ∼ 500 K. The hysteresis is characterized by the coercivity field, Hc, decreasing between ∼100 and 75 Oe when T is increased from 5 to 510 K. The values of Hc are in reasonable agreement with the effect of the largest MnSb inclusions. The maximum of M (T), measured in the zero-field-cooled and the field-cooled conditions in a weak field of 500 Oe, is observed at T ∼ 510 K and is attributable to the Hopkinson effect. [ABSTRACT FROM AUTHOR]