Results 1 - 10 of 67
Results 1 - 10 of 67. Search took: 0.018 seconds
|Sort by: date | relevance|
[en] We have investigated structural, magnetic, and transport properties of Fe(Sb1-xTex)2 single crystals. Whereas metallic ground state is induced for x = 0.001, canted antiferromagnetism is observed for 0.1 (le) x (le) 0.4 with an intermediate ferromagnetic phase for x = 0.2. With higher Te doping, semiconducting behavior is restored and the variable range hopping conduction mechanism dominates at low temperatures for 0.4 (le) x (le) 0.6. We discuss our results within the framework of inverted metal to insulator in correlated electron insulators.
[en] We present critical fields, thermally activated flux flow (TAFF), and critical current density of tetragonal phase β-FeSe single crystals. The upper critical fields Hc2(T) for H (parallel) (101) and H (perpendicular) (101) are nearly isotropic and are likely governed by the Pauli limiting process. The large Ginzburg-Landau parameter Κ ∼ 72.3(2) indicates that β-FeSe is a type-II superconductor with a smaller penetration depth than in Fe(Te, Se). The resistivity below Tc follows Arrhenius TAFF behavior. For both field directions below 30 kOe, single-vortex pinning is dominant, whereas collective creep becomes important above 30 kOe. The critical current density Jc from M-H loops for H (parallel) (101) is about five times larger than for H (perpendicular) (101), yet much smaller than in other iron-based superconductors.
[en] Thermally activated flux flow (TAFF) and flux-flow Hall effect (FFHE) of Fe(Te,S) single crystal in the mixed state are studied in magnetic fields up to 35 T. Thermally activated energy (TAE) is analyzed using conventional Arrhenius relation and modified TAFF theory which is closer to experimental results. The results indicate that there is a crossover from single-vortex pinning region to collective creep pinning region with increasing magnetic field. The temperature dependence of TAE is different for H (parallel) ab and H (parallel) c. On the other hand, the analysis of FFHE in the mixed state indicates that there is no Hall sign reversal. We also observe scaling behavior |ρxy(H)|=Aρxx(H)β.
[en] Polarized Raman scattering spectra of the Fe1-xCoxSb2 and Fe1-xCrxSb2 (0 (le) x (le) 1) single crystals are measured at room temperature in the 80-200 cm-1 wavenumber range. All six Raman-active modes, predicted by factor-group analysis, are experimentally observed and assigned. We also analyzed energy and linewidth changes for all six Raman-active modes caused by doping.
[en] The vibrational properties of ErTe3 were investigated using Raman spectroscopy and were analyzed on the basis of peculiarities of the RTe3 crystal structure. Four Raman active modes for the undistorted structure, predicted by factor-group analysis, are experimentally observed and assigned according to diperiodic symmetry of the ErTe3 layer. By analyzing temperature dependence of the Raman mode energy and intensity, we have provided clear evidence that all Raman modes, active in the normal phase, are coupled to the charge-density waves. In addition, new modes have been observed in the distorted state.
[en] We have measured polarized Raman scattering spectra of the Fe1-xCoxSb2 and Fe1-xCrxSb2 (0 (le) x (le) 0.5) single crystals in the temperature range between 15 and 300 K. The highest energy B1g symmetry mode shows significant line asymmetry due to phonon-mode coupling-width electronic background. The coupling constant achieves the highest value at about 40 K and after that it remains temperature independent. Origin of additional mode broadening is pure anharmonic. Below 40 K the coupling is drastically reduced, in agreement with transport properties measurements. Alloying of FeSb2 with Co and Cr produces the B1g mode narrowing, i.e., weakening of the electron-phonon interaction. In the case of Ag symmetry modes we have found a significant mode mixing.
[en] We report results of our infrared and optical spectroscopy study of a half-metallic ferromagnet Mn5Ge3. This compound is currently being investigated as a potential injector of spin-polarized currents into germanium. Infrared measurements have been performed over a broad frequency (70-50000 cm-1) and temperature (10-300 K) range. From the complex optical conductivity σ(ω), we extract the electron self-energy Σ(ω). The calculation of Σ(ω) is based on numerical algorithms for solution of systems of nonlinear equations. The obtained self-energy provides insight into electron correlations in Mn5Ge3. In particular, it reveals that charge carriers may be coupled to bosonic modes, possibly of magnetic origin.
[en] We have investigated the upper critical field anisotropy and magnetotransport properties of Fe1.14(1)Te0.91(2)S0.09(2) single crystals in stable magnetic fields up to 35 T. The results show that μ0Hc2(T) along the c axis and in the ab plane exhibit saturation at low temperatures. The anisotropy of μ0Hc2(T) decreases with decreasing temperature, becoming nearly isotropic for T → 0. Our analysis indicates that the spin-paramagnetic pair breaking with spin-orbital scattering is responsible for the behavior of μ0Hc2(T). Furthermore, from analysis of the normal-state properties, we show evidence that the excess Fe is a key factor determining the normal- and superconducting-state physical properties.
[en] In this work, we investigated the temperature dependence of the upper critical field μ0Hc2(T) of Fe1.02(3)Te0.61(4)Se0.39(4) and Fe1.05(3)Te0.89(2)Se0.11(2) single crystals by measuring the magnetotransport properties in stable dc magnetic fields up to 35 T. Both crystals show that μ0Hc2(T) in the ab plane and along the c-axis exhibit saturation at low temperatures. The anisotropy of μ0Hc2(T) decreases with decreasing temperature, becoming nearly isotropic when the temperature T → 0. Furthermore, μ0Hc2(0) deviates from the conventional Werthamer-Helfand-Hohenberg theoretical prediction values for both field directions. Our analysis indicates that the spin-paramagnetic pair-breaking effect is responsible for the temperature-dependent behavior of μ0Hc2(T) in both field directions.
[en] We report muon spin rotation spectra in the narrow-gap semiconductors FeGa3 and FeSb2 consistent with a narrow band of small spin polarons (SPs). The characteristic sizes obtained for these SPs are RFeGa#sub 3# ∼ 0.3-0.6 nm and RFeSb#sub 2# ∼ 0.3 nm, respectively. Such SP states are expected to originate from the exchange correlations between localized and itinerant electrons. Our data suggest that SP bands are formed at low temperature, but are destroyed by thermal fluctuations above 10 K in FeGa3 and above 7 K in FeSb2. Formation of such SP band states can explain many of the low-temperature properties of these materials.