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1.
The thermal conductivity ( κ) of single crystals of tetragonal uniaxial antiferromagnets USb 2 ( T N = 202 K) and UBi 2 ( T N = 180.8 K) has been measured along the a-axis ( κa ) over the temperature range from 0.5 to 300 K and along the c-axis ( κc ) from 0.5 to 70 K. The as-grown samples have residual resistivity ratio (RRR) values of about 500–600 and 100–150 for UBi 2 and USb 2, respectively. The anisotropy of the thermal conductivity ( κa ( T)/ κc ( T) ~ 5) and the low- T Lorenz ratios are discussed in relation to Fermi surface topology for both compounds. 相似文献
2.
We report measurements of the specific heat C
p( T), electrical resistivity ϱ( T) and magnetic susceptibility ξ( T) of hexagonal CePd 2In, at low temperatures. Anomalies in C
p( T), χ( T) and ϱ( T) at T=1.23 K, indicate a phase transition, most likely to an antiferromagnetically-ordered phase. The electronic entropy reaches R ln2 per mole Ce at 9.2K, suggesting that the phase transition involves a doublet state. The ordered phase coexists with moderately
correlated itinerant electrons. 相似文献
3.
Resistivity (ρ), thermal conductivity ( k) and Seebeck coefficient ( S) of La 1–xCe xB 6 single crystals with various concentrations of cerium Ce ions was measured in a wide temperature range 3?300 K. The obtained data were analyzed in the framework of the Coqblin–Shrieffer model. The contributions of scattering of carriers on magnetic ions Ce for all transport parameters ρ( T), k( T), S( T) are revealed. Strong dependence of the magnetic scattering on concentration of the cerium ions are identified. The anomalous behavior of the transport parameters ρ( T), k( T), S( T) in the region near 30 K is attributed to the Δ ~ 30 K splitting of Г8 level. 相似文献
4.
We present measurements of the resistivity tensor components ρ a ( T) and ρ c ( T) of high-quality Tl 2Ba 2Ca 2Cu 3O 10 single crystals wit Tc = 118 … 121 K. The in-plane resistivity ρ a as well as the out-of-plane resistivity ρ c show a metal-like temperature dependence with an anisotropy ratio ρ c/ρ a of up to 10 3. The coherence length ξ c (0) = 0.15 nm could be determined from an analysis of the fluctuation conductivity above Tc. From measurements of the ac-susceptibility in magnetic fields up to 10 Tesla the temperature dependence of the depinning line could be obtained. The diffusion coefficient of the flux lines obtained from the frequency dependence of the depinning temperature shows a thermally activated behaviour of the flux motion in the field range 0.1 T ? B ? 10 T. 相似文献
5.
Measurements of the basal-plane resistivity ρ
a( T, H) performed on highly oriented pyrolitic graphite, with magnetic field H∥ c-axis in the temperature interval 2–300K and fields up to 8 T, provide evidence for the occurrence of both field-induced and
zero-field superconducting instabilities. Additionally, magnetization M( T, H) measurements suggest the occurrence of Fermi surface instabilities which compete with the superconducting correlations.
Fiz. Tverd. Tela (St. Petersburg) 41, 2135–2138 (December 1999) 相似文献
6.
The heat capacity (C
P), the thermal diffusion (η), the thermal conductivity (κ), and the electrical resistance of the La0.825Sr0.175MnO3 single crystal have been measured in the temperature range 80–350 K in magnetic fields to 40 kOe. Dependences C
P(T), κ(T), and η(T) have anomalies near T
C, which are suppressed in magnetic field. The minima in dependences κ(T) and η(T) near T
C are explained by the phonon scattering on fluctuations of the magnetic order parameter. Dependences κ(T) and η(T) have anomalies near T
S = 200 K related to the structural transition from the rhombohedral (R) to the orthorhombic (O*) phase. 相似文献
7.
Electrical resistivity measurements have been performed on the system Mn 5?x,Fe xSi 3 for the compounds x = 0,1,2,3,4 and 5 from 4.2 K to above room temperature. From the shape of the ρ( T) curves it can be inferred that the transition from antiferromagnetic to ferromagnetic ordering occurs in the concentration range 3 ? x ? 4; for Fe 5Si 3 and MnFe 4Si 3 the ρ( T) curves are characterized by a break in their slope, whereas for x = 1,2 and 3 a large minimum appears. Mn 5Si 3 exhibits two successive minima at 74 and 105 K. Magnetic susceptibility measurements for x = 1, 2 and 3 give confirmation of the Néel temperature for x = 1 and 2, whereas for x = 3 the behaviour is more complex. 相似文献
8.
The behavior of the electrical resistivity ρ( T), the superconducting transition temperature T c , and the upper critical field H c2( T) of a polycrystalline sample of YNi 2B 2C irradiated by thermal neutrons with the subsequent high-temperature isochronous annealing in the temperature interval T ann = 100–1000°C has been studied. It has been found that the irradiation of YNi 2B 2C with a fluence of 10 19cm ?2 leads to the suppression of the superconductivity. The final disordered state is reversible; i.e., the initial ρ( T), T c , and H c2( T) values are almost completely recovered upon annealing at up to T ann = 1000°C. The quadratic dependence ρ( T) = ρ 0 + a 2 T 2 is observed for the sample in the superconducting state ( T c = 5.5?14.5 K). The coefficient a 2 (proportional to the square of the electron mass m*) hardly changes. The form of the dependence of T c on ρ 0 can be interpreted as the suppression of the two superconducting gaps, Δ 1 and Δ 2 (Δ 1 ~ 2Δ 2). The degradation rate of Δ 1 is about three times higher than that of Δ 2. The dependences dH c2/ dT on ρ 0 and T c may be described by the relations for a superconductor in the intermediate limit (the coherence length ζ 0 is on the order of the electron mean free path l tr) under the assumption of a nearly constant electron density of states on the Fermi level N( E F). The observed behavior of T c obviously does not agree with the widespread opinion about the purely electron-phonon mechanism of superconductivity in the compounds of this type supposing the anomalous type of superconducting pairing. 相似文献
9.
For a 2D electron system in silicon, the temperature dependence of the Hall resistance ρ xy( T) is measured in a weak magnetic field in the range of temperatures (1–35 K) and carrier concentrations n where the diagonal resistance component exhibits a metallic-type behavior. The temperature dependences ρ xy( T) obtained for different n values are nonmonotonic and have a maximum at Tmax ~ 0.16 TF. At lower temperatures T < Tmax, the change δρ xy( T) in the Hall resistance noticeably exceeds the interaction quantum correction and qualitatively agrees with the semiclassical model, where only the broadening of the Fermi distribution is taken into account. At higher temperatures T > Tmax, the dependence ρ xy( T) can be qualitatively explained by both the temperature dependence of the scattering time and the thermal activation of carriers from the band of localized states. 相似文献
10.
The electrical resistivity ρ( T) of the band ferromagnets Co 2FeZ (where Z = Al, Si, Ga, Ge, In, Sn, and Sb are s- and p-elements of Mendeleev’s Periodic Table) has been investigated in the temperature range 4.2 K < T < 1100 K. It has been shown that the dependences ρ( T) of these alloys in a magnetically ordered state at temperatures T < T C are predominantly determined by the specific features of the electronic spectrum in the vicinity of the Fermi level. The processes of charge carrier scattering affect the behavior of the electrical resistivity ρ( T) only in the vicinity of the Curie temperature T C and above, as well as in the low-temperature range (at T ? T C). 相似文献
11.
Analysis of Soffer's size-effect theory for electrical resistivity shows, for measurements in such a T range for which the temperature dependent portion of the resistivity, ρ i, is always much smaller than the residual bulk resistivity ρ ∞(0) of the metal studied, that while size-effects leave the essential T dependence of ρi unchanged, it may increase its absolute value and the observed residual resistivity ρ(0), thus explaining recent results of Caplin et al. This also corrects the general conclusion arrived at by the latter authors, i.e. that the T dependence of ρ of a metal foil of given residual resistivity is the same as that of a bulk sample of the same residual resistivity provided that the latter is governed by impurity scattering, as being true for a narrow T range only, i.e. for which ρi( T) ? ρ∞(0). However, for this T range a procedure is outlined which allows one to extract values of the surface specularity parameter pS and also ρ∞ of the metal foils studied. 相似文献
12.
The polycrystalline samples La 0.67Ca 0.33Mn (1?x)Fe x O 3 ( x?=?0.00,?0.01,?0.03, and 0.1) have been grown in single phase by solid state route. The analysis of the reaction has been done by thermogravimetry and differential thermal analysis measurements. DC electrical resistivity measurements have been carried out down to 15?K. The samples with x?=?0.00, 0.01, and 0.03 exhibit metal–insulator (MI) transition at temperatures 221.5?K, 217?K, and 215?K respectively, whereas the sample with x?=?0.1 is insulating in nature for entire temperature range. Interestingly, the electric transport properties of these samples are not consistent with their magnetic phase transitions and the samples show MI transition at a temperature, T MI, which is significantly lower than the paramagnetic to ferromagnetic transition temperature ( T c). The resistivity data below T MI has been analyzed using the empirical relation ρ?=?ρ 0?+?ρ 1 T n and the data above this temperature has been analyzed using two existing models, Mott's variable range hopping model and spin polaronic conduction model. 相似文献
13.
Approximating the shape of the magneto-thermoelectric power (TEP) Δ S( T, H) measured in Bi 2Sr 2CaCu 2O y by an asymmetric linear triangle of the form Δ S( T, H)≃ S
p
( H)± B
±( H)( T
c
− T) with positive B
−( H) and B
+( H) defined below and above T
c
, we observe that B
+( H) ≃2 B
−( H). To account for this asymmetry, we explicitly introduce the field-dependent chemical potential μ( H) of holes into the Ginzburg-Landau theory and calculate both an average Δ S
av( T, H) and fluctuation contribution Δ S
fl( T, H) to the total magneto-TEP Δ S( T, H). As a result, we find a rather simple relationship between the field-induced variation of the chemical potential in this
material and the above-mentioned magneto-TEP data around T
c
, viz. Δ μ( H)∝ S
p
( H).
Zh. éksp. Teor. Fiz. 116, 257–262 (July 1999)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
14.
成功制备了超导临界温度为27 K的K0.8Fe2Se2晶体,并详细研究了晶体c轴向的载流子输运特性.结合X射线衍射、光学显微镜下的形貌、变温电阻率的测试结果表明,样品存在有"相分离",但是这类层状铁基超导体材料的两个相不是简单沿c轴向层状交替排布的,而应该是沿着c轴向存在弱联系的金属相链接通路,金属相部分形成近3维的空间网状链接模式.热导率测试和复阻抗谱z(ω,T0)的研究表明超导晶体沿着c轴方向存在有大量的相界面,所束缚的极化电荷致使相对介电常数达到106数量级,相应地在10 MHz附近出现负的相位特征. 相似文献
15.
Electronic and magnetic properties of RuSr 2GdCu 2O 8 have been investigated by resistivity, magnetization and NMR measurements. Magnetic order ( T
C=133 K) and superconducting transition ( T
S(onset) 52 K) have been confirmed in RuSr 2GdCu 2O 8. We observed two kinds of Ru-NMR signals (the hyperfine fields of 101Ru are 590 kOe and 290 kOe), suggesting a possible charge segregation of Ru 4+( S=1) and Ru 5+( S=3/2) in the RuO 2 layers. Holes can be inherently doped in the CuO 2 layers from the (Ru 4+, Ru 5+)O 2 layers, and the superconductivity can occur under weak magnetic interactions between Ru and Cu spins in RuSr 2GdCu 2O 8. 相似文献
16.
We report on syntheses and electron transport properties of polycrystalline samples of diborides (AB 2) with different transition metals atoms (A=Zr, Nb, Ta). The temperature dependence of resistivity, ρ( T), and ac susceptibility of these samples reveal a superconducting transition of ZrB 2 with T c =5.5 K, while NbB 2 and TaB 2 have been observed to be nonsuperconducting up to 0.37K. H c2( T) is linear in temperature below T c , leading to a rather low H c2(0)=0.1 T. At T close to T c , H c2( T) demonstrates a downward curvature. We conclude that these diborides, as well as MgB 2 samples, behave like simple metals in the normal state with usual Bloch-Grüneisen temperature dependence of resistivity and with Debye temperatures 280, 460, and 440 K for ZrB 2, NbB 2, and MgB 2, respectively, rather than T 2 and T 3, as previously reported for MgB 2. 相似文献
17.
The structure, electrical resistivity, and magnetoresistance of predominantly oriented La 0.67Ca 0.33MnO 3(30 nm)/LaAlO 3 films are investigated after partial relaxation of biaxial mechanical stresses. The negative magnetoresistance MR of the films reaches a maximum at T = 235–240 K. The full width at half-maximum of the peak in the curve MR(T) for a film is five to six times greater than that for a manganite layer grown on a substrate with a small lattice mismatch. For T < 150 K, the temperature dependence of the electrical resistivity ρ of the films is fitted well by the relationship ρ = ρ 0 + ρ 1 (H)T 4.5, where ρ 0 ≡ ρ( T = 4.2 K) and ρ 1( H) is a parameter that is independent of temperature but dependent on the magnetic field H. The parameter ρ 1( H = 0) for the La 0.67Ca 0.33MnO 3(30 nm)/LaAlO 3 films is several times larger than that for thin manganite layers only weakly strained by the substrate. The electrical resistivity ρ 1 decreases almost linear as the quantity μ 0 H increases in the field range 1–5 T. 相似文献
18.
We report measurements of the temperature dependence of the electrical resistivity, ρ( T), and magnetic pen-etration depth, λ( T), for polycrystalline samples of Eu 0.5K 0.5Fe 2As 2 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 Eu 3+ moments.
The article is published in the original. 相似文献
19.
We study medium modifications of the dilepton e + e ? and μ +μ ? mass spectra in coherent photo-and electroproduction of ρ 0(1 S)-and ρ′(2 S)-meson resonances on nuclear targets. The analysis is performed within the coupled ρ 0(1 S), ρ′(2 S), ... channel formalism, where nuclear modifications derive from off-diagonal rescatterings. We find that the effect of off-diagonal rescatterings on the shape of the dilepton-mass spectrum in the ρ 0(1 S)-meson mass region is only marginal, but it is very important in the ρ′(2 S) mass region. The main off-diagonal contribution in the ρ′(2 S) mass region comes from the sequential mechanism γ* → ρ 0(1 S) → ρ′(2 S), which dominates ρ′(2 S) production for heavy nuclei. Our results also show that, in the ρ′(2 S) mass region, there is a considerable interference of the Breit-Wigner tail of the amplitude for the decay ρ 0(1 S) to e + e ? and μ +μ ? with the amplitude for the decay of ρ′(2 S) to e + e ? and μ +μ ?. 相似文献
20.
The electrical properties of (Co 45Fe 45Zr 10) x(Al 2O 3) 1−x
granular nanocomposites have been studied. The concentration dependences of electrical resistivity are S-shaped (in accordance with the percolation theory of conduction) with a threshold at a metallic component concentration of
∼41 at. %. An analysis of the temperature behavior carried out in the range 300–973 K revealed that structural relaxation
and crystallization of the amorphous phase are accompanied by a decrease in the electrical resistivity of the composites above
the percolation threshold and by its increase below the percolation threshold. For metallic phase concentrations x<41 at. %, variable range hopping conduction over localized states near the Fermi level was found to be dominant at low temperatures
(77–180 K). A further increase in temperature brings about a crossover of the conduction mechanism from Mott’s law ln(σ) ∝
(1/ T) 1/4 to ln(σ) ∝ (1/ T) 1/2. A model of inelastic resonance tunneling over a chain of localized states of the dielectric matrix was used to find the
average number of localized states involved in the charge transport between metallic grains.
__________
Translated from Fizika Tverdogo Tela, Vol. 46, No. 11, 2004, pp. 2076–2082.
Original Russian Text Copyright ? 2004 by Kalinin, Remizov, Sitnikov. 相似文献
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