Resistivity ρ(T) and absolute thermoelectric power S(Τ) have been measured for USb single crystals characterized by different residual resistivity ratios, RRR = ρ(300 K)/ρ(4.2 K). A 50 μV/K peak of S(Τ) observed at 40 K for high RRR crystal vanishes for low RRR one. The ρ ∝ Τ^{4} dependence observed below 40 K changes to the ρ ∝ Τ^{5/2} one. These variations are ascribed to reduction of the magnon drag effect by an increased incoherent magnetic scattering of carriers, possibly induced by a small change of composition. Resistivity anomaly is analysed above the antiferromagnetic transition temperature T_{N}. We have found that resistivity decreases as tlnt in the range 0.02 ≤ t ≤ 0.35, where t = (Τ - T_{N})/T_{N}. It is ascribed to a semimetallic character of this compound.
We present results of extensive measurements of magnetic susceptibility, electrical resistance, specific heat and thermoelectric power of two series of solid solutions GdNi_{x}Ga_{4-x} and GdCu_{x}Ga_{4-x}, for ranges of doping x from 0.6 to 1 and from 1 to 1.5, respectively. All studied phases display the Curie-Weiss behaviour of magnetic susceptibility and antiferromagnetic ordering at temperatures below 23 K. Substitution of gallium with transition metal atoms has strong influence on Néel temperatures of all studied phases, shifting them by few K, depending on x. Metamagnetic-like anomalies are observed for some compositions. Behaviour of the electrical resistivity reveals metallic nature of all samples. Their magnetic ordering is reflected in low-temperature anomalies of the resistivity and the heat capacity.
Single crystals of ErPdBi were grown from Bi-flux. The crystal structure of MgAgAs-type was confirmed using X-ray diffraction. Magnetization, magnetic susceptibility, electrical resistance and heat capacity measurements revealed an antiferromagnetic phase transition at T_{N} = 1.2 K. At high temperatures, the electrical resistance has a semiconducting-like character (dR/dT < 0 ). The resistance starts decreasing with decreasing T below 15 K and shows a very sharp drop below T_{N} but remains finite down to 0.4 K. Hence, no obvious evidence of superconductivity was found in the electrical transport data. On the other hand, the real part of AC magnetic susceptibility is negative below T_{C} = 1.6 K and its imaginary component has a clear maximum at this temperature that might be associated with the onset of superconducting state. The electrical resistance revealed Shubnikov-de Haas oscillations in magnetic fields 8-33 T. Their amplitude decreases with increasing T and disappears above 10 K. Cyclotron mass determined from this dependence is 0.21 m_{e}.
High quality single crystals of some representatives of half-Heusler family were grown from Bi-flux. For single crystals characterization, X-ray diffraction and scanning electron microscopy techniques were used. The low-temperature physical properties of the synthesized crystals were determined by means of magnetization, magnetic susceptibility, electrical resistivity and heat capacity measurements. For each compound but LuPtBi, the electrical resistivity varies in a semimetallic manner at high temperatures, and exhibits a metallic character at low temperatures. LuPtBi is metallic in the whole temperature range studied. The bismuthides HoPdBi, LuPdBi, LuPtBi and YPtBi were found superconducting below the critical temperature T_{c} = 0.7, 1.8, 0.9, and 0.96 K, respectively. For the compounds GdPdBi, DyPdBi and HoPdBi, an antiferromagnetic ordering was found to set in below T_{N} = 12.8, 3.7, and 1.9 K, respectively. HoPdBi is thus an intriguing material in which both cooperative phenomena coexist.
A single-crystalline sample of disordered ferromagnetic U₂NiSi₃ was investigated by means of electrical resistivity measurements under ambient and high hydrostatic pressure. Temperature dependences of the electrical resistivity clearly reveal interplay of the ferromagnetic ordering and quantum interference effects resulting from crystallographic disorder. Electron-electron interaction manifests itself as a T^{0.5} increase in the in-plane and out-of-plane electrical resistivity below 5 K. Weak localization is observed solely in the ab-plane as a linear-in-T contribution to resistivity, which suggests that internal magnetic field does not break the interference of scattered electron waves in ab-plane. Applied hydrostatic pressure does not affect the T^{0.5} electron-electron interaction contribution, however it diminishes the impact of weak localization on the ab-plane resistivity.
Transverse magnetoresistivity (H ∥ [001]; and current ∥ [110]) of U_{3}As_{4} has been measured in field up to 35 T. An abrupt change of the magnetoresistivity behaviour from saturated (low field) to unsaturated (high field) type was observed at the spin reorientational transition (19.1 T at 4.2 K). The transition is accompanied by a peak in the magnetoresistivity. The behaviour is ascribed to fractional spin polarization of the band electrons.
Magnetisation and longitudinal magnetoresistance of single-crystal samples of two compositions: stoichiometric compound U_3P_4 and its solid solution U_3(P,As)_4 (with As:P ratio close to 1) were measured in pulsed magnetic fields with strength up to 47 T, and in temperatures from 4 K up to few tens of kelvins above the Curie temperatures (135 K and 181 K for both compositions, respectively). Field was always applied along a hard magnetic direction [100]. Magnetisation experiments showed no sign of expected magnetic-moment-reorientation transition and data look quantitatively similar for both compositions. On the other hand, longitudinal magnetoresistance (MR) is remarkably different for each composition. Onset of the above mentioned transition can be held responsible for broad maxima observed in MR(B) curves for U_3(P,As)_4. Values of magnetic field strength corresponding to these maxima follow a linear dependence on temperature. We assume that these features of MR(B) curves are due to progressive deformation of magnetic structure of U_3(P,As)_4 in high magnetic fields.
Single crystals of TbPdBi, a representative of the group of half-Heusler bismuthides, were studied by means of magnetic susceptibility, heat capacity, electrical resistivity, magnetostriction and thermal expansion measurements. The compound was characterized as an antiferromagnet with the Néel temperature T_{N} ≈5.3 K. Neutron diffraction experiment confirmed the antiferromagnetic ordering and yielded the propagation vector k=(1/2,1/2,1/2). Remarkably, this k vector is in accord with the recently developed theory of antiferromagnetic topological insulators.
Single-crystals of LuSb were investigated by means of electrical resistivity and magnetoresistance measurements. The compound was found to exhibit giant magnetoresistance exceeding 3000%, low-temperature resistivity plateau, and Shubnikov-de Haas oscillations. It was characterized as a semimetal with nearly balanced contributions of electron and hole carriers to the magnetotransport properties. The experimental findings, supported by the results of electronic structure calculations, proved that the magnetotransport in LuSb can be described in the scope of 3D multi-band Fermi surface model without topologically non-trivial electronic states.
In this paper we investigate electron emission/capture from/to the DX state of indium in CdTe by means of high pressure freeze-out cycle and steady-state photo-conductivity experiments. The results indicate that the DX state is occupied by two electrons. A comparison with deep level transient spectroscopy data shows that two-electron emission occurs at low temperatures, while one-electron emission takes place at high temperatures.
We present experimental evidence that at high pressures indium donors in CdTe localize electrons in spatially correlated manner. We have studied Hall mobility, μ_{H}, as a function of electron concentration, n_{H}, at T=77 K. Changes of n_{H} have been achieved by two methods. High pressure freeze-out of electrons onto localized states of In-donors leads to the mobility enhancement with respect to the situation when n_{H} has been modified by means of a subsequent annealing of the sample. As a result, depending on the degree of spatial correlations in the impurity charges arrangement, different values of μ_{H} correspond to the same value of n_{H}. The variation of mobility with electron concentration suggests that the localized state of In-donor represents likely negatively charged DX state.
Room temperature, continuous wave operation of InGaN multi-quantum wells laser diodes made by rf plasma assisted molecular beam epitaxy at 411 nm wavelength is demonstrated. The threshold current density and voltage were 4.2 kA/cm^2 and 5.3 V, respectively. High optical power output of 60 mW was achieved. The lifetime of these laser diodes exceeds 5 h with 2 mW of optical output power. The laser diodes are fabricated on low dislocation density bulk GaN substrates, at growth conditions which resembles liquid phase epitaxy. We demonstrate that relatively low growth temperatures (600-700°C) pose no intrinsic limitations for fabrication of nitride optoelectronic components by plasma assisted molecular beam epitaxy.
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