共查询到20条相似文献,搜索用时 15 毫秒
1.
B.-S. Jeong S.J. Pearton Y.W. Heo D.P. Norton A.F. Hebard 《Journal of magnetism and magnetic materials》2008
Hall effect measurements were performed on epitaxial CoxTi1−xO2–δ thin films grown on (0 0 1) LaAlO3 by reactive RF magnetron co-sputter deposition. Magnetization measurements reveal ferromagnetic behavior in M–H loop at room temperature for CoxTi1−xO2–δ thin films for which x?0.02. An anomalous Hall effect was observed for Co0.10Ti0.90O2−δ films grown with the partial pressure of water P(H2O)=4×10−4 Torr or less. These films exhibit a positive ordinary Hall coefficient and a positive magnetoresistance. X-ray diffraction on films grown under these conditions shows evidence for TinO2n−1 phase due to the deficiency of oxygen. In contrast, Hall measurements taken for undoped and Co-doped TiO2 thin films grown under more oxidizing conditions show only the ordinary Hall effect with a negative Hall coefficient consistent with n-type conduction. For these films, the magnetoresistance was positive and increased monotonically with increasing magnetic field. The results suggest that Co-doped TinO2n−1 may be a dilute magnetic semiconducting oxide for which the carriers couple to the spin polarization. 相似文献
2.
N.N. Loshkareva A.V. Korolyov N.I. Solin E.V. Mostovshchikova Yu.P. Sukhorukov S.V. Naumov A.M. Balbashov 《Journal of magnetism and magnetic materials》2006
The magnetic, transport, and optical properties of electron-doped Ca1−xLaxMnO3−δ single crystals with x ?0.12 were studied. The magnetic measurements show that in single crystals with x=0 and 0.05 the G-type AFM phase with weak FM component is realized and in crystals with x=0.10 and 0.12 the G- and C-type AFM phases coexist. The C-type magnetic structure arises at less concentration of La than in polycrystalline samples as a result of oxygen vacancies being additional source of electrons. Under magnetic transitions in the G- and C-type phases, resistivity and magnetoresistance of the doped single crystals have anomalies. Optical absorption in IR range indicates formation of a charge gap in crystals with x=0.10 and 0.12 at appearance of the C-AFM and monoclinic phase with orbital/charge ordering. By comparing optical and transport properties, heterogeneous electronic state and its relation with heterogeneous magnetic state are shown. 相似文献
3.
In this work, we report on the physical properties of good-quality polycrystalline superconducting samples of La2−xSrxCu1−yZnyO4−δ (y=0, 0.02) prepared by a wet-chemical method, focusing on the temperature dependence of the critical current. Using the wet-chemical method, we were able to produce samples with improved homogeneity compared to the solid-state method. A complete set of samples with several carrier concentrations, ranging from the underdoped (strontium concentration x≈0.05) to the highly overdoped (x≈0.25) region, were prepared and investigated. The X-ray diffraction analysis, zero-field cooling magnetization and electrical resistivity measurements were reported on earlier. The structural parameters of the prepared samples seem to be slightly modified by the preparation method and their critical temperatures were lower than reported in the literature. The temperature dependence of the critical current was explained by a theoretical model which took the granular structure of the samples into account. 相似文献
4.
N. Balchev K. Nenkov V. Antonov J. Pirov B. Kunev 《Physica C: Superconductivity and its Applications》2010,470(22):2040-2046
Samples with nominal compositions MoSnxSr2YCu2O8−δ (0 ? x ? 0.075) were synthesized and their superconducting and magnetotransport properties were investigated. It was established that the optimum Sn-doping (x = 0.02 and 0.03) increases the Tc of the undoped MoSr2YCu2O8−δ. The upper critical fields of the samples were determined using magnetization, susceptibility and resistivity measurements. It was established that the Sn-doping weakly affects the first and the intragrain second critical field of Mo-1212 but enhances the extrapolated to T = 0 (i.e. the intergrain) upper critical field. The observed phenomena were discussed on the basis of the Josephson-junction-arrays model. A phenomenological expression describing the temperature dependency of the susceptibility of Mo-1212 was found. 相似文献
5.
Nanocrystalline Ca1−xHoxMnO3−δ (0?x?0.3) manganites were synthesized as phase-pure by a simple and instantaneous solution autogel combustion method, which is a low temperature initiated synthetic route to obtain fine grain size. All the samples, heated at 800 °C for 18 h, can be produced as phase-pure; the polycrystalline powders are homogeneous and possess ultrafine particle size. The holmium-doped calcium manganites retain the orthorhombic phase of the undoped sample. The scanning electron microscope (SEM) images revealed that the combustion-derived compounds exhibit particle size that decreases with holmium content from 300 to 80 nm. All manganites show two active IR vibrational modes near 400 and 600 cm−1. The high temperature dependence of resistivity was measured using a standard four-probe method in the range 25-600 °C. All the samples exhibit semiconductor behaviour and holmium induces a marked decrease in the electrical resistivity when compared with the parent CaMnO3. The results can be well attributed to the Mn4+/Mn3+ ratio and to the particle grain size. 相似文献
6.
E. Farber M. Lewkowicz B. Gorshunov J.P. Contour 《Journal of Physics and Chemistry of Solids》2008,69(12):3082-3084
This report presents a study of the temperature dependence of the penetration depth in Y1−xCaxBa2Cu3O7−δ thin films, which shows that a contribution to the order parameter from phase fluctuations in optimally doped samples cannot be excluded, and demonstrates the appearance of an imaginary component in the order parameter in overdoped samples. Measurements were performed using two complementary techniques: the parallel plate resonator (PPR), operated at 10 GHz, and far infrared (FIR) transmission, where the absolute value of the penetration depth can be obtained. 相似文献
7.
Frank J. Berry Xiaolin Ren Peter Slater 《Journal of Physics and Chemistry of Solids》2008,69(8):2032-2036
We report here on the fluorination of the perovskite-related phases La1−xSrxFe1−yCoyO3−δ. The introduction of fluorine in place of oxygen is achieved through a low-temperature (400 °C) reaction with poly(vinylidene fluoride). X-ray powder diffraction data show that in all cases the fluorination leads to an expansion in the unit cell, which is consistent with partial replacement of oxygen by fluorine and consequent reduction in the oxidation state of iron and/or cobalt. This reduction in oxidation state is confirmed by X-ray absorption- and Mössbauer-spectroscopy. The Mössbauer spectra show complex magnetically split hyperfine patterns for the fluorinated samples, reflecting the interactions between Fe3+ ions, which are not possible in oxides containing Fe4+. 相似文献
8.
La1−xCaxMnO3+δ (0.0?x?1.0) samples were prepared and their resistivity and Seebeck coefficients were measured in the high-temperature range. Ca doping changes the ratio of Mn3+/Mn4+ and influences the electronic transport behavior markedly. With the increase of Ca concentration, the samples change from a p-type semiconductor to an n-type one and Seebeck coefficient becomes increasingly negative. Low doping (x=0.2) and high doping (x=0.8) induces the drop of the resistivity compared with undoped LaMnO3+δ and CaMnO3+δ samples due to the rise of carrier concentration. However, the resistivity of moderate-doped samples (x=0.4, 0.6) is larger than low- and high-doped samples because dopant scattering decreases carrier mobility. 相似文献
9.
J.W. Lee G.M. Shin S.H. Moon S.I. Yoo 《Physica C: Superconductivity and its Applications》2010,470(20):1253-1256
We report a successful fabrication of high-Jc GdBa2Cu3O7−δ (GdBCO) films by the metal–organic deposition process on the LaAlO3 (LAO) (0 0 1) substrates. The coating solution was prepared by mixing Gd, Cu fluorine-free sources with Ba trifluoroacetate. Samples were dip-coated, pyrolized within 3 h at the temperature up to 400 °C in a humid oxygen atmosphere, and finally fired at various high temperatures in 100 ppm Ar/O2 atmosphere. The GdBCO films fired at 775 and 800 °C exhibited Jc values of ∼2.1 MA/cm2 at 77 K in a self-field, which are attributable to both high Tc,zero values of ∼89 K and high in-plane textures of 1.3–1.4°. Above 800 °C, however, the superconducting properties of GdBCO films are degraded due to the thermal decomposition of GdBCO film in 100 ppm Ar/O2 atmosphere. 相似文献
10.
Systematic valence changes in Pr1−xSrxMn1−yInyO3−δ upon cation substitution with Sr2+ and In3+ have been found using Mn K-edge and Pr L-edge X-ray absorption, and Mn LII,III and Pr MIV,V electron energy-loss spectroscopy. The average valence of the praseodymium ions is close to +3.0 and virtually constant over the sample set when the samples also contained manganese ions. Pr0.5Sr0.5InO3−δ showed a distinct increase in the praseodymium valence state. In contrast, the average valence of the manganese ions changed from the trivalent state to intermediate values between +3.0 and +4.0 and approached the tetravalent state depending on the level of substitution. The knowledge of the valence is required to understand the conduction mechanisms in the material due to the small polaron hopping (electronic conductivity) and motion of oxygen ions along the vacancies (ionic conductivity). Addition of strontium and indium led to the formation of oxygen vacancies. A previously assumed intermediate valence of praseodymium as causal factor for the higher oxygen catalytic activity cannot be confirmed with room temperature measurements. 相似文献
11.
V.A. Atsarkin A.A. Generalov A.E. Mefed O.Yu. Gorbenko E.J. Roy 《Journal of magnetism and magnetic materials》2009,321(19):3198-3202
Temperature and frequency dependencies of the real (χ′) and imaginary (χ″) parts of the dynamic magnetic susceptibility were studied experimentally in fine particles of La-Ag manganites prepared by various methods. The samples under study have the Curie points in the range TC=42-48 °C, which is a medical hyperthermia range of interest. When approaching TC from below, a critical peak of χ″ was revealed, followed by a steep drop while passing to the paramagnetic phase. The experiments on the magnetic radio-frequency (RF) heating of the manganite aqueous suspensions demonstrated good autostabilization of the temperature near TC. Peculiar instability is found in the heating kinetics, caused by the observed critical behavior of the RF losses. The prospects of the La-Ag manganites as candidates for application in the temperature-controlled hyperthermia are discussed. 相似文献
12.
N.T. Bagraev O.N. Guimbitskaya L.E. Klyachkin A.A. Kudryavtsev A.M. Malyarenko V.V. Romanov A.I. Ryskin I.A. Shelykh A.S. Shcheulin 《Physica C: Superconductivity and its Applications》2010,470(19):893-896
Planar CdBxF2−x–p-CdF2–CdBxF2−x sandwich nanostructures prepared on the surface of the n-type CdF2 bulk crystal are studied to register the spin transistor and quantum spin Hall-effects. The current–voltage characteristics of the ultra-shallow p+–n junctions verify the CdF2 gap, 7.8 eV, and the quantum subbands of the 2D holes in the p-type CdF2 quantum well confined by the CdBxF2−xδ-barriers. The temperature and magnetic field dependencies of the resistance, specific heat and magnetic susceptibility demonstrate the high temperature superconductor properties for the CdBxF2−xδ-barriers. The value of the superconductor energy gap, 2Δ = 102.06 meV, determined by the tunneling spectroscopy method appears to be in a good agreement with the relationship between the zero-resistance supercurrent in superconductor state and the conductance in normal state, πΔ/e, at the energies of the 2D hole subbands. The results obtained are evidence of the important role of the multiple Andreev reflections in the creation of the high spin polarization of the 2D holes in the edged channels of the sandwich device. The high spin hole polarization in the edged channels is shown to identify the mechanism of the spin transistor and quantum spin Hall-effects induced by varying the top gate voltage, which is revealed by the first observation of the Hall quantum conductance staircase. 相似文献
13.
Y. Yu Q.Q. Liu C.Q. Jin Y.C. Li X.D. Li J. Liu 《Physica C: Superconductivity and its Applications》2009,469(14):843-845
The high-pressure angle-dispersive X-ray diffraction experiments on the NdBa2Cu3O6+δ superconductor were performed from ambient to above 30 GPa at room temperature. The structure analysis based on the Rietveld refinement methods shows the different pressure dependence for the bond length between the basal-plane copper of the pyramids to the apical oxygen (denoted Cu(2)–O(1)) and bond length between basal-plane copper to plane oxygen (denoted Cu(2)–O(2,3)). The ambient bulk modulus B0 is derived as 127 GPa. A possible correlation between Cu(2)–O(1) and Tc was discussed. 相似文献
14.
W.J. Li B.C. ZhaoR. Ang W.H. SongY.P. Sun Yuheng Zhang 《Journal of magnetism and magnetic materials》2006
A series of the double-doping samples La(2+4x)/3Sr(1−4x)/3Mn1−xCuxO3(0?x?0.2) with the Mn3+/Mn4+ ratio fixed at 2:1 have been prepared. The structural, magnetic, transport properties and magnetoresistance of the series samples have been investigated. It is found that no apparent crystal structure change is introduced by Cu doping up to x=0.20. But the Curie temperature TC and magnetization M are strongly affected by Cu substitution. A remarkable magnetotransport behavior, characterized by double bumps, is observed, and an obvious low-temperature upturn is found in the range of 0.07?x?0.12. As a result, the temperature range of colossal magnetoresistance (CMR) is greatly broadened. Moreover, it is found that the room temperature magnetoresistance (MR) of double-doping samples is obviously larger that the undoped La2/3Sr1/3Mn1−xCuxO3 at 300 K, which can give a guide for the adequate selection of the room temperature CMR materials. 相似文献
15.
S. Nagao P. Mele K. Matsumoto A. Ichinose M. Mukaida Y. Yoshida S. Horii R. Kita 《Physica C: Superconductivity and its Applications》2010,470(20):1304-1307
We report the microstructure change of BaSnO3 (BSO)–YBa2Cu3O7−x (YBCO) thin film system grown on SrTiO3 single crystal substrates by pulsed laser deposition with using the “surface-modified-target” and “mixture-target” methods. Although it was confirmed that the thick BSO nanorods incorporated to YBCO films act as strong artificial pinning centers, the formation mechanism of the nanorods is still unclear. The purpose of this work is to extend the structural investigation to higher contents of BSO (up to 71 vol.%) in order to enlighten the relationship among interfacial energy, morphology and pinning performance in binary BSO–YBCO films. 相似文献
16.
The dielectric properties of Cu0.5Tl0.5Ba2Ca3Cu4O12−δ superconductor samples were studied at 79 and 290 K by means of capacitance (C) and conductance (G) measurements with the test frequency (f) in the range of 10 kHz to 10 MHz. A negative capacitance (NC) phenomenon has been observed, which is most likely arising due to higher Fermi level of ceramic superconductor samples than metal electrodes. Also the NC may be due to the space charge located at the multiple insulator–superconductor interfaces (grain boundaries) in the materials. The negative dielectric constant (ε′) and loss factor (tan δ) show strong dispersion at low frequencies. The lower thermal agitation at 79 K may enhance the polarizability and hence the dielectric constants (ε′ and ε″). 相似文献
17.
C. Decorse-Pascanut J. Berthon N. Dragoe 《Journal of magnetism and magnetic materials》2009,321(20):3526-3531
Magnetic properties of bulk SrTi1−xCoxO3−δ solid solutions (for x from 0 to 0.05), prepared in air as those partially reduced, were studied by following the influence of the dopant concentration and valence. A strong paramagnetic and/or diamagnetic contribution and an extremely weak ferromagnetic contribution maintained up to room temperature is observed for all the studied compositions, including the undoped samples. While the paramagnetic contribution shows a classical evolution with cobalt concentration and valence, the ferromagnetic part of the magnetization seems to be independent of the doping process. While some of the observations can support the assumption of an intrinsic property of the SrTiO3 matrix, the hypothesis of a ferromagnetism associated to some contamination with external magnetic impurities cannot be completely discarded and will be retained here. 相似文献
18.
Magnetic and transport properties in double-doping La(2+4x)/3Sr(1−4x)/3Mn1–xCuxO3 (0⩽x⩽0.20) systems
A series of the double-doping samples La(2+4x)/3Sr(1−4x)/3Mn1–xCuxO3(0?x?0.2)with the Mn3+/Mn4+ ratio fixed at 2:1 and the single-doping samples La2/3Sr1/3Mn1–xCuxO3(0?x?0.2) have been investigated. For the double-doping samples, though the ratio Mn3+/Mn4+=2:1 has been generally recognized the optimum ratio, the Curie temperature TC and metallic–insulator transition temperature Tp1 are more rapidly decreased by Cu substitution than that corresponding to single-doping samples. And the resistivity ρ value for the double doping is larger about two or three orders of magnitude than that corresponding to single doping. At the same time, two resistivity peaks and two magnetoresistance (MR) peaks appear. We suggest that for the double-doping samples the A-site cation size 〈rA〉 and the A-site mismatch factor σ2 decreases with increasing doping level, which leads to the system microstructural distortion. This microstructural distortion makes the Mn3+–O–Mn4+ cut off more cluster-spin except for the clusters induced by Cu. These cluster interfaces contribute to ρ, which exceeds far the contribution of eg electron decreasing with doping increasing in the single doping. At the same time, such interface scattering also gives rise to the appearance of second peak for the double-doping samples. The experimental results shows that double doping could be also a potential way in tuning colossal MR (CMR), which can give a guide for the adequate selection of CMR materials. 相似文献
19.
We report STM/STS observations on the 4a×4a charge order in the pseudogap (PG) and superconducting (SC) states of Bi2Sr2CaCu2O8+δ, and suggest that the charge order is associated with incoherent quasiparticle or pair states around the antinodal fermi surface (FS), which are also responsible for the PG, and it can coexist with the superconductivity caused by the pairing of coherent quasiparticles on the nodal fermi arc. We also suggest that the nanometer-scale gap inhomogeneity in the SC state, reported previously [Pan, et al., Nature 413 (2001) 282; Mommo, et al., J. Phys. Soc. Jpn. 74 (2005) 2400; Hashimoto, et al., Phys. Rev. B74 (2006) 064508] arises from that in the PG state, which occurs around the antinodal FS. 相似文献
20.
J. Janaki A. Bharathi N. Gayathri P. Yasodha M. Premila V.S. Sastry Y. Hariharan 《Physica B: Condensed Matter》2008,403(4):631-635
Studies on some new members of the cobalt perovskite Gd1−xSrxBaCo2O5+δ with low strontium concentrations (0<x<0.1) have been carried out with the aim of investigating possible metallization of the GdBaCo2O5+δ system by hole doping. Low temperature electrical resistivity, magnetic susceptibility and thermopower of the above system have been studied. The pristine compound with x=0 and δ∼0.5 exhibits a semiconductor-like behavior and two magnetic transitions below room temperature. Upon Sr2+ substitution, there is a fall in resistivity by 2-3 orders of magnitude at low temperature and also a dramatic reduction in the ferromagnetic to antiferromagnetic transition temperature. These changes can be explained on the basis of hole doping (and increase in the Co4+content). Evidence for an increase in Co4+ with Sr2+ substitution is provided by iodometric analysis. 相似文献