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1.
Resonant magnetic X-ray scattering was employed to investigate the magnetic state of epitaxial a* oriented thin films of the heavy fermion superconductor UNi2Al3. The observed incommensurate propagation vector as well as the Ne
l temperature correspond to
those of bulk samples. The 1200
film shows magnetic order with a correlation length >800 ? parallel to the growth axis. Out of the three possible magnetic
domains the one with the moment direction perpendicular to the film surface is not realized. 相似文献
2.
V. R. Shaginyan 《JETP Letters》2004,80(4):263-266
The main properties and the type of the field-tuned quantum critical point in the heavy-fermion metal CeCoIn5 that arise upon application of magnetic fields B are considered within a scenario based on fermion condensation quantum phase transition. We analyze the behavior of the effective mass, resistivity, specific heat, charge, and heat transport as functions of applied magnetic fields B and show that, in the Landau Fermi liquid regime, these quantities demonstrate critical behavior, which is scaled by the critical behavior of the effective mass. We show that, in the high-field non-Fermi liquid regime, the effective mass exhibits very specific behavior, M*~ T? 2/3, and the resistivity demonstrates T2/3 dependence. Finally, at elevated temperatures, it changes to M*~T?1/2, while the resistivity becomes linear in T. In zero magnetic field, the effective mass is controlled by temperature T and the resistivity is also linear in T. The obtained results are in good agreement with recent experimental facts. 相似文献
3.
The structure, electrical resistivity, and magnetoresistance of (50-nm)La0.67Ca0.33MnO3 epitaxial films grown on a [(80 nm)Ba0.25Sr0.75TiO3/La0.3Sr0.7Al0.65Ta0.35O3] substrate with a substantial positive lattice misfit have been studied. The tensile biaxial strains are shown to account for the increase in the cell volume and in the relative concentration of Mn+3 ions in the manganite films as compared to those for the original material (33%). The peak in the temperature dependence of the resistivity ρ of La0.67Ca0.33MnO3 films was shifted by 30–35 K toward lower temperatures relative to its position in the ρ(T) graph for a manganite film grown on (001)La0.3Sr0.7Al0.65Ta0.35O3. For T < 150 K, the temperature dependences of ρ of La0.67Ca0.33MnO3/Ba0.25Sr0.75TiO3/La0.3Sr0.7Al0.65Ta0.35O3 films could be well fitted by the relation ρ = ρ0 + ρ1T4.5, where ρ0 = 0.35 mΩ cm and the coefficient ρ1 decreases linearly with increasing magnetic field. In the temperature interval 4.2–300 K, the magnetoresistance of manganite films was within the interval 15–95% (μ0H = 5 T). 相似文献
4.
V. V. Brazhkin E. Bychkov O. B. Tsiok 《Journal of Experimental and Theoretical Physics》2017,125(3):451-464
High-precision studies of the volume and the electrical resistivity of g-As2Te3 glasses at a high hydrostatic pressure up to 8.5 GPa at room temperature are performed. The glasses exhibit elastic behavior in compression only at a pressure up to 1 GPa, and a diffuse structural transformation and inelastic density relaxation (logarithmic in time) begin at higher pressures. When the pressure increases further, the relaxation rate passes through a sharp maximum at 2.5 GPa, which is accompanied by softening the relaxing bulk modulus, and then decreases, being noticeable up to the maximum pressure. When pressure is relieved, an unusual inflection point is observed in the baric dependence of the bulk modulus near 4 GPa. The polyamorphic transformation is only partly reversible and the residual densification after pressure release is 2%. In compression, the electrical resistivity of the g-As2Te3 glasses decreases exponentially with increasing pressure (at a pressure up to 2 GPa); then, it decreases faster by almost three orders of magnitude in the pressure range 2–3.5 GPa. At a pressure of 5 GPa, the electrical resistivity reaches 10–3 Ω cm, which is characteristic of a metallic state; this resistivity continues to decrease with increasing pressure and reaches 1.7 × 10–4 Ω cm at 8.1 GPa. The reverse metal–semiconductor transition occurs at a pressure of 3 GPa when pressure is relieved. When the pressure is decreased to atmospheric pressure, the electrical resistivity of the glasses is below the initial pressure by two–three orders of magnitude. Under normal conditions, both the volume and the electrical resistivity relax to quasi-equilibrium values in several months. Comparative structural and Raman spectroscopy investigations demonstrate that the glasses subjected to high pressure have the maximum chemical order. The glasses with a higher order have a lower electrical resistivity. The polyamorphism in the As2Te3 glasses is caused by both structural changes and chemical ordering. The g-As2Te3 compound is the first example of glasses, where the reversible metallization under pressure has been studied under hydrostatic conditions. 相似文献
5.
S. A. Ahmed 《Applied Physics A: Materials Science & Processing》2008,92(3):565-570
Thermoelectric power and electrical resistivity measurements on polycrystalline samples of Bi2Se3 and stoichiometric ternary compound in the quasi-binary system SnSe–Bi2Se3 in the temperature range of 90–420 K are presented and explained assuming the existence of an impurity band. The variation
of the electron concentration with temperature above 300 K is explained in terms of the thermal activation of a shallow donor,
by using a single conduction band model. The density of states effective mass m
*=0.15m
0 of the electrons, the activation energy of the donors, their concentration, and the compensation ratio are estimated. The
temperature dependence of the electron mobility in conduction band is analyzed by taking into account the scattering of the
charge carriers by acoustic phonon, optical phonon, and polar optical phonon as well as by alloy and ionized impurity modes.
On the other hand, by considering the two-band model with electrons in both the conduction and impurity bands, the change
in the electrical resistivity with temperature between 420 and 90 K is explained. 相似文献
6.
We report measurements of the temperature dependence of the electrical resistivity, ρ(T), and magnetic pen-etration depth, λ(T), for polycrystalline samples of Eu0.5K0.5Fe2As2 with T
c
= 31 K. ρ(T) follows a linear temperature dependence above T
c
and bends over to a weaker temperature dependence around 150 K. The magnetic penetration depth, determined by radio frequency
technique displays an unusual minimum around 4 K which is associated with short-range ordering of localized Eu3+ moments.
The article is published in the original. 相似文献
7.
Banarji Behera Pratibindhya Nayak Ram N. P. Choudhary 《Central European Journal of Physics》2008,6(2):289-295
A polycrystalline sample of KCa2Nb5O15 with tungsten bronze structure was prepared by a mixed oxide method at high temperature. A preliminary structural analysis
of the compound showed an orthorhombic crystal structure at room temperature. Surface morphology of the compound shows a uniform
grain distribution throughout the surface of the sample. Studies of temperature variation on dielectric response at various
frequencies show that the compound has a transition temperature well above the room temperature (i.e., 105°C), which was confirmed
by the polarization measurement. Electrical properties of the material have been studied using a complex impedance spectroscopy
(CIS) technique in a wide temperature (31–500°C) and frequency (102–106 Hz) range that showed only bulk contribution and non-Debye type relaxation processes in the material. The activation energy
of the compound (calculated from both the loss and modulus spectrum) is same, and hence the relaxation process may be attributed
to the same type of charge carriers. A possible ‘hopping’ mechanism for electrical transport processes in the system is evident
from the modulus analysis. A plot of dc conductivity (bulk) with temperature variation demonstrates that the compound exhibits
Arrhenius type of electrical conductivity.
相似文献
8.
R.G. Abhilash Kumar K. Vinod U. Syamaprasad 《Applied Physics A: Materials Science & Processing》2007,88(2):243-247
MgB2/Fe wires were prepared by electrical self-heating of in situ powder-in-tube wires for the first time at ambient conditions.
Characterization of the wires processed at 750 °C, 800 °C and 850 °C for 15 min by XRD, SEM, ϱ–T, susceptibility and JC measurements shows that the MgB2 formed is of high quality particularly with respect to phase purity and transport JC. The method considerably reduces the overall energy consumption vis-à-vis the production cost, simplifies the complexity
of the fabrication procedure and is promising for manufacture of high-quality MgB2 superconducting wires.
PACS 74.70.Ad; 74.62.Bf; 74.25.Fy; 74.25.Ha; 81.20.Hy 相似文献
9.
A. M. Vora 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2008,43(6):293-300
Theoretical computation of the pressure dependence of superconducting state parameters of a binary Ca70Mg30 metallic glass has been performed using the model potential formalism. Explicit expressions have been derived for the volume dependence of the electron-phonon coupling strength λ and the Coulomb pseudopotential μ*, considering the variation of the Fermi momentum k F and Debye temperature θD with volume. Well-known Ashcroft’s empty core model pseudopotential and five different types of the local-field correction functions, namely, Hartree, Taylor, Ichimaru-Utsumi, Farid et al. and Sarkar et al. have been used for obtaining pressure dependence of transition temperature T C and the logarithmic volume derivative Φ of the effective interaction strength N 0 V for the metallic glass superconductor. It has been obtained that T C of Ca70Mg30 metallic glass decreases rapidly with increasing pressure up to 60% decrease in the volume, for which the μ* and Φ curves show a linear nature. The superconducting phase disappears at about 60% decrease in the volume. 相似文献
10.
A. Esmaeili H. Sedghi M. Amniat-Talab M. Talebian 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,79(4):443-447
The fluctuation conductivity measurement on the new Y-based Y3Ba5Cu8O18-
x
superconductor is presented. The dimensional crossovers between different temperature regimes were analyzed with Aslamazov-Larkin
(AL) theory and a good quantitative agreement was achieved for the experimental data. For our data, the mean field regime
is dominated by 2D AL fluctuations. Our results reveal the occurrence of critical fluctuation regime in consistent with the
prediction of the full dynamic 3D XY model. We found the dynamical critical exponent to be z = 3.4 for our data. We analyzed also the excess conductivity data by Hikami-Larkin theory and estimated the phase relaxation
time. 相似文献
11.
The compression of a Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) is investigated at room temperature up to 24 GPa using in-situ high pressure energy dispersive
X-ray diffraction with a synchrotron radiation source. The pressure-induced structural relaxation is exhibited. It is found
that below about 8 GPa, the existence of excess free volume contributes to the rapid structural relaxation, which gives rise
to the rapid volumetric change, and the structural relaxation results in the structural stiffness under higher pressure. 相似文献
12.
The structure, electrical resistivity, and magnetotransport parameters of 20-nm-thick epitaxial La0.67Ba0.33MnO3 films grown by laser ablation on LaAlO3(001) substrates are studied. The unit cell volume V eff = 58.80 Å3 of the as-grown manganite films is found to be less than that for bulk La0.67Ba0.33MnO3 crystals. Maximum values of the negative magnetoresistance MR(μ0 H = 1 T) = ?0.27 for La0.67Ba0.33MnO3 films are observed at a temperature of about 225 K. For 5 < T < 100 K, the film magnetoresistance depends only weakly on temperature and is on the order of ?0.1. At temperatures below 100 K and for 3 < μ0 H < 5 T, the electrical resistivity of the as-grown films decreases linearly with increasing magnetic field. 相似文献
13.
The electrical conductivity of V3O5 single crystals has been investigated over a wide temperature range, including the region of existence of the metallic phase
and the region of the transition from the metallic phase to the insulating phase. It has been shown that the low electrical
conductivity of metallic V3O5 is caused, on the one hand, by a lower concentration of electrons and, on the other hand, by a strong electronelectron correlation
whose role with decreasing temperature increases as the phase transition temperature is approached. The temperature dependence
of the electrical conductivity of the insulating phase of V3O5 has been explained in the framework of the theory of hopping conduction, which takes into account the effect of thermal vibrations
of atoms on the resonance integral. 相似文献
14.
Spin-wave resonances have been observed in superlattices arising due to the phase separation and self-organization of charge carriers in Eu0.8Ce0.2Mn2O5 single crystals. The resonances are found within the 5–80 K temperature range at frequencies close to 30 GHz. Similar resonances with intensities about an order of magnitude lower are also observed in EuMn2O5. The latter suggests the existence of charge transfer processes between the manganese ions of different valences in EuMn2O5. 相似文献
15.
The behavior of the electrical resistivity and magnetoresistance of 40-to 120-nm-thick La0.67Ca0.33MnO3 films grown on differently oriented lanthanum aluminate substrates was studied. The cell volume in thin (40 nm) La0.67Ca0.33MnO3 films grown coherently on (001)LaAlO3 was found to be substantially smaller. Mechanical stress relaxation in biaxially strained La0.67Ca0.33MnO3 films is accompanied by an increase in the cell volume. The temperatures at which the electrical resistivity and magnetoresistance in biaxially strained La0.67Ca0.33MnO3 films were maximum can differ by 60–70 K from those observed in bulk single crystals. 相似文献
16.
N. V. Melnikova N. I. Kadyrova A. V. Tebenkov I. S. Ustinova Yu. G. Zaynulin A. N. Babushkin 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(8):1121-1123
The results from experimental investigations on the effect of high pressures (10–50 GPa) on the electrical properties and
magnetoresistance of the perovskite-like high-pressure state of CaCoCu2V4O12 are presented. The pressure ranges of substantial changes in the behavior of electrical characteristics are determined. 相似文献
17.
D. P. Kozlenko S. V. Ovsyannikov V. V. Shchennikov V. I. Voronin B. N. Savenko 《JETP Letters》2007,85(4):203-207
Pressure dependences of the thermopower and electrical resistivity of the La0.75Ca0.25MnO3 manganite are measured in the pressure range 0–20 GPa at room temperature. The absolute value of the thermopower increases in the pressure range 0–3 GPa and decreases at higher pressures. At the same time, the electrical resistivity decreases over the entire pressure range. It is found that the competing effect of the closing of the bandgap, which is determined by the activation energy for the thermopower, and the pressure broadening of the d bands is the cause of the observed behavior of the thermoelectric properties of La0.75Ca0.25MnO3, which is untypical for the majority of dielectrics and semiconductors with single-band unipolar conductivity in the absence of phase transitions and is accompanied by a change in the sign of the pressure coefficient of the thermopower. The interrelation between the magnetic and thermoelectric properties of manganites under pressure is analyzed in the framework of the double exchange model. The causes of the considerable decrease in the pressure coefficients of the insulator-metal transition and Curie temperatures under pressure experimentally observed in manganites are discussed. 相似文献
18.
S. V. Demishev A. V. Semeno H. Ohta S. Okubo Yu. B. Paderno N. Yu. Shitsevalova N. E. Sluchanko 《Applied magnetic resonance》2009,35(2):319-326
A recently discovered magnetic resonance in the orbitally ordered phase of CeB6 (orbital ordering resonance) is studied in a wide frequency range v = 44–360 GHz. The g-factor for this resonance was found to increase with frequency from g(v = 44 GHz) ∼ 1.55 to g(v > 250 GHz) ∼ 1.7. In addition to the orbital ordering resonance, a new magnetic resonance with a g-factor of 1.2–1.3 was detected for frequencies exceeding 200 GHz.
Presented at the 5th Asia-Pasific EPR/ESR Symposium, August 24–27, 2006, Novosibirsk, Russian Federation. 相似文献
19.
A. G. Gamzatov A. B. Batdalov O. V. Melnikov O. Yu. Gorbenko 《Bulletin of the Russian Academy of Sciences: Physics》2009,73(9):1304-1306
The low-temperature minimum of the La0.85Ag0.15MnO3 resistivity has been investigated. The analysis of the experimental data shows that this minimum of resistivity in zero magnetic
field and the large magnetoresistive effect, which increases with a decrease in temperature, can be explained within the model
of spin-polarized tunneling of carriers through grain boundaries. 相似文献
20.
Binary icosahedral and crystalline phases of the Zr70Pd30 alloy were obtained in crystallization from the amorphous state during heat treatment. The specific heat and electrical resistivity of the icosahedral, amorphous, and crystalline phases were measured and compared. An increase in the electronic density of states on the Fermi surface, lattice softening, and an increase in the electron-phonon coupling constant were observed to occur with decreasing structural order. Despite the high valence electron density in the icosahedral phase, where the electronic densities of states are twice those in the crystal, the electrical resistivity of the icosahedral phase is ~50 times as high. Superconductivity was observed for the first time in the icosahedral phase of a binary system of transition metal atoms, Zr70Pd30. 相似文献