共查询到20条相似文献,搜索用时 46 毫秒
1.
Davinder Kaur 《低温学》2005,45(6):455-462
In the present study we report the measurements of microwave surface resistance (Rs) of YBCO thin films on LaAlO3 substrate as a function of temperature, thickness and magnetic field by microstrip resonator technique. The Tc(R = 0) of the films is 90 K and Jc > 106 A/cm2 at 77 K. The microwave surface resistance has been measured for films of various thicknesses. The value of Rs has been found to be initially decreased with increasing film thickness due to increase in number of defects. A minimum microwave surface resistance has been obtained for film thickness of about 300 nm. The increase of Rs with film thickness above 300 nm is possibly due to degradation of the film microstructure as observed with Atomic Force Microscopy. Temperature dependence of surface resistance has been studied for best quality films. The field induced variations of surface resistance are also investigated by applying dc magnetic field perpendicular to stripline structure and surface of the film. A general linear and square field dependence of Rs at low and high value of fields has been observed with critical field value of 0.4 T which confirms the microwave dissipation induced by flux flow in these resonators at 10 GHz frequency. The hysteresis of Rs in dc field observed for field value above critical field shows the higher value of surface resistance in decreasing field than in increasing field which is in agreement with one state critical model and is a characteristic of homogeneous superconductors. 相似文献
2.
We report on a heterogeneous precipitation method to modify the surfaces of La0.67Ca0.33MnO3 (LCMO) grains with CuO. It is shown that such a modification causes transport and magnetoresistance (MR) properties of the composites largely different from that observed in pure LCMO granular system. Especially, a significant enhancement in MR is observed near the insulator-metal transition temperature (TIM). The maximum MR reaches as high as ∼88 and ∼90% at a low magnetic field of 0.3 T for the modified samples of LCMO/xCuO with x = 4 and 15 mol%, respectively. Compared to pure LCMO, the CuO-modified samples have a substantial decrease in resistivity (ρ) at the temperature regions apart TIM. Furthermore, for the x = 4% sample, a considerable thermal hysteresis is observed at the same temperature region where abnormal MR effect appears. On the basis of magnetization measurement and structural analysis, a possible interpretation for the experimental observations is presented. 相似文献
3.
Akiyuki Matsushita Kazunori Fukuda Yuh Yamada Fumihiro Ishikawa Syun Sekiya Takashi Naka 《Science and Technology of Advanced Materials》2007,8(6):477-483
We present studies of the thermal, magnetic, and electrical transport properties of reduced polycrystalline Pr2Ba4Cu7O15−δ (Pr247) showing a superconducting transition at Tc=10-16 K, and compare them with those of as-sintered non-superconducting Pr247. The electrical resistivity in the normal state exhibited T2 dependence up to approximately 150 K. A clear specific heat anomaly was observed at Tc for Pr247 reduced in a vacuum for 24 h, proving the bulk nature of the superconducting state. By the reduction treatment, the magnetic ordering temperature TN of Pr moments decreased from 16 to 11 K, and the entropy associated with the ordering increased, while the effective paramagnetic moments obtained from the DC magnetic susceptibility varied from 2.72 to 3.13μB. The sign of Hall coefficient changed from positive to negative with decreasing temperature in the normal state of a superconducting Pr247, while that of the as-sintered one was positive down to 5 K. The electrical resistivity under high magnetic fields was found to exhibit Tα dependence (α=0.08-0.4) at low temperatures. A possibility of superconductivity in the so-called CuO double chains is discussed. 相似文献
4.
Synthesis and electrical properties of cubic NaxWO3 thin films across the metal-insulator transition
Highly oriented (1 0 0) NaxWO3 thin films were fabricated in the composition range 0.1 ≤ x ≤ 0.46 by pulsed laser deposition technique. The films showed transition from metallic to insulating behaviour at a critical composition between x = 0.15 and 0.2. The pseudo-cubic symmetry of NaxWO3 thin films across the transition region is desirable for understanding the composition controlled metal-insulator transition in the absence of any structural phase transformation. The electrical transport properties exhibited by these films across the transition regime were investigated. While the resistivity varied as T2 at low temperatures in the metallic regime, a variable range hopping conduction was observed for the insulating samples. For metallic compositions, a non-linear dependence of resistivity in temperature was also observed from 300 to 7 K, whose exponent varied with the composition of the film. 相似文献
5.
The temperature dependence of the electrical resistivity in (1 − x) La0.7Ca0.3MnO3 + xAg composites has been investigated between 5 and 300 K for H = 0 and 3T. Ag addition has increased the conductivity of this system. Curie temperature (TC) is almost independent of Ag content and is ~ 260 K for all the samples, while the metal-insulator transition temperature (TMI) increases with increasing content of Ag. The ρ-T of all samples fit well with the phenomenological percolation approach, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. In addition, all the samples clearly reveal the unusual low temperature resistivity minimum. Analysis of our results in terms of the model based on charge carrier tunneling between the anti-ferromagnetically coupled grains shows excellent agreement with the experiment data for both H = 0 and 3T. 相似文献
6.
S.E. Lofland J.D. Hettinger K.V. Ramanujachary P. Gall 《Materials Research Bulletin》2007,42(7):1230-1241
Synthesis, structure and electronic properties are reported on single crystals of Sm4Mo18O32 and Nd4Mo18O32. The triclinic crystal structure has three distinctly different Mo metal atom clusters (Mo2, Mo4 and Mo6), which extend in complex chains. The temperature dependence of the electrical resistivity displays a broad minimum around 150-200 K with a pronounced increase in the 30-50 K range. However, unlike the related monoclinic reduced Mo oxides, A4Mo18O32 (A = Y, Gd-Yb), there is no true metal-insulator transition in the Sm and Nd analogs. We discuss these observations in terms of correlations among the Mo clusters. 相似文献
7.
Tino Jaeger Christian MixMichael Schwall Xeniya KozinaJoachim Barth Benjamin BalkeMartin Finsterbusch Yves U. IdzerdaClaudia Felser Gerhard Jakob 《Thin solid films》2011,520(3):1010-1014
Due to their exceptional thermoelectric properties Half-Heusler alloys like MNiSn (M = Ti,Zr,Hf) have moved into focus. The growth of single crystalline thin film TiNiSn and Zr0.5Hf0.5NiSn by dc magnetron sputtering is reported. Seebeck and resistivity measurements were performed and their dependence on epitaxial quality is shown. Seebeck coefficient, specific resistivity and power factor for Zr0.5Hf0.5NiSn at room temperature were measured to be 63 μV K− 1, 14.1 μΩ m and 0.28 mW K− 2 m− 1, respectively. Multilayers of TiNiSn and Zr0.5Hf0.5NiSn are promising candidates to increase the thermoelectric figure-of-merit by decreasing thermal conductivity perpendicular to the interfaces. The epitaxial growth of multilayers containing TiNiSn and Zr0.5Hf0.5NiSn is demonstrated by measuring satellite peaks in the X-ray diffraction pattern originating from the additional symmetry perpendicular to the film surface. 相似文献
8.
I. Chaitanya Lekshmi 《Materials Research Bulletin》2005,40(1):93-104
Highly oriented SrMoO3 thin films have been fabricated by pulsed laser deposition of SrMoO4 in hydrogen. The films are found to grow along the (1 0 0) direction on LaAlO3 (1 0 0) and SrTiO3 (1 0 0) substrates. The method has been extended for the fabrication of oxynitride thin films, using ammonia as the reducing medium. The resistivity measurements show nonlinear temperature dependent (Tn) behaviour in the temperature interval of 10-300 K. The conduction mechanism is largely affected by the strain due to the substrate lattice. A combination of T and T2 dependence of resistivity on temperature is observed for films having lesser lattice mismatch with the substrate. The X-ray photoelectron spectroscopic studies confirm the formation of SrMoO3 and SrMoO3−xNx films. 相似文献
9.
The studies of the specific heat, electrical resistivity and thermoelectric power of YbNi4Si are reported. These studies are supported by magnetic susceptibility and X-ray photoemission spectroscopy (XPS) measurements. YbNi4Si does not order magnetically down to 4 K. Nearly in the whole temperature range studied the magnetic susceptibility follows a Curie law with μeff = 4.15 μB/f.u. This effective magnetic moment is close to the value expected for the 4f13 configuration (4.54 μB). The Yb2+ and Yb3+ peaks observed by XPS in the valence band region confirm the domination of the Yb3+ valence state. Based on the specific heat measurements, the electronic specific heat coefficient γ = 25 mJ/mol/K2 and the Debye temperature θD = 320 K were derived. A quadratic dependence of electrical resistivity at low temperatures has been observed. The Kadowaki-Woods ratio has been discussed. The thermoelectric power has been analyzed in the framework of the two band model. 相似文献
10.
The effects of electrode on the resistive switching in Nd0.7Ca0.3MnO3(NCMO)/YBa2Cu3O7(YBCO) heterostructure are investigated at room temperature. For Cu/NCMO/YBCO, resistance can be switched on-and-off from a high- to low-resistance state at a steady ratio of 25% with a pulsed-voltage of ± 3 V. On the other hand, a giant resistance-change as large as 1350% is observed with ± 5 V for Ag/NCMO/YBCO with a fast decay down to 550%. Our experimental results show clear evidences that the nature of interfaces can be modified by the electric field and it dictates the resistive switching behavior of these heterostructure devices, which are the potential candidates for the random access memory. 相似文献
11.
S.A. Lokare 《Materials Research Bulletin》2008,43(2):326-332
Electrical and magnetoelectric properties of magnetoelectric (ME) composites containing barium titanate as electrical component and a mixed Ni-Co-Mn ferrite as the magnetic component are reported. The ME composites with a general formula (x)BaTiO3 + (1 − x)Ni0.94Co0.01Mn0.05Fe2O4 where x varies as 0, 0.55, 0.70, 0.85 and 1 were prepared by standard double sintering ceramic method. The presence of both the phases was confirmed by X-ray diffraction technique. The dc resistivity was measured as a function of temperature. The variation of dielectric constant (?) and loss tangent (tan δ) with frequency (100 Hz-1 MHz) and with temperature was studied. The conduction is explained on the basis of small polaron model based on ac conductivity measurements. The static value of ME conversion factor i.e. dc (ME)H was studied as function of intensity of magnetic field. The changes were observed in dielectric properties as well as ME effect as the molar ratio of the components was varied. A maximum value of ME conversion factor of 610 μV/cm Oe was observed in the case of a composite containing 15 mol% ferrite phase. 相似文献
12.
Unipolar resistive switching behavior has been investigated in Pt/Co3O4/Pt stacks. The resistance ratio of the high- and low- resistance states is over 5 × 103. The “ON/OFF” operation of the memory cells can be repeated more than 200 times at room temperature. The resistance of the two states can be kept for more than 16 h without showing degradation. The temperature dependence of the resistance shows a metallic behavior at the low-resistance state, but a semiconductor-behavior at the high-resistance state. The mechanism responsible for the observed unipolar resistive switching behavior has been discussed. 相似文献
13.
Electrical resistivity, magnetoresistance (MR), temperature coefficient of resistance (TCR) and magnetocaloric effect of (1 − x) Pr2/3Ba1/3MnO3:x PdO (x = 0-30 mol% PdO) composite manganites are reported here. Pristine sample Pr2/3Ba1/3MnO3 (PBMO) shows two insulator-metal like transitions (TP1 ~ 194 K and TP2 ~ 160 K) in the electrical resistivity behavior. With PdO, TP1 becomes sharper whereas TP2 disappears beyond 10 mol% PdO addition. The intrinsic MR gets enhanced from 22% for the pristine sample to ~ 42% for 27% PdO sample. However, the extrinsic MR is found to decrease in the composites. The TCR also increases from a negligible value for PBMO to 8% for 25 mol% PdO sample. These features have been explained on the basis of opening of new conducting channels and decrease in spin dependent scattering and the overall decrease in electrical resistivity. The magnetic entropy change and relative cooling power (RCP) for the PBMO sample are 5.3418 J.Kg-K and 304.5428 J/Kg respectively. However, these values decrease in the composites. 相似文献
14.
L. De Los Santos Valladares D. Hurtado Salinas A. Bustamante DominguezD. Acosta Najarro S.I. KhondakerT. Mitrelias C.H.W. BarnesJ. Albino Aguiar Y. Majima 《Thin solid films》2012,520(20):6368-6374
In this work, we study the crystallization and electrical resistivity of the formed oxides in a Cu/SiO2/Si thin film after thermal oxidation by ex-situ annealing at different temperatures up to 1000 °C. Upon increasing the annealing temperature, from the X ray diffractogram the phase evolution Cu → Cu + Cu2O → Cu2O → Cu2O + CuO → CuO was detected. Pure Cu2O films are obtained at 200 °C, whereas uniform CuO films without structural surface defects such as terraces, kinks, porosity or cracks are obtained in the temperature range 300-550 °C. In both oxides, crystallization improves with annealing temperature. A resistivity phase diagram, which is obtained from the current-voltage response, is presented here. The resistivity was expected to increase linearly as a function of the annealing temperature due to evolution of oxides. However, anomalous decreases are observed at different temperatures ranges, this may be related to the improvement of the crystallization and crystallite size when the temperature increases. 相似文献
15.
Michio Mikawa Toshihiro Moriga Yukinori Misaki Ichiro Nakabayashi 《Materials Research Bulletin》2005,40(6):1052-1058
Transparent conducting oxide (TCO) films in the ZnO-In2O3 system were prepared by a pulsed laser deposition method. A target that consists of the mixture of ZnO and In2O3 powders was used. Influences of the target composition x (x = [Zn]/([Zn] + [In])) and heater temperature on structural, electrical and optical properties of the TCO films were examined. Introduction of oxygen gas into the chamber during the deposition was necessary for improvement in the transparency of the deposited films. The amorphous phase was observed for a wide range of x = 0.20-0.60 at 110 °C. Minimum resistivity was 2.65 × 10−4 Ω cm at x = 0.20. The films that showed the minimum resistivity had an amorphous structure and the composition shifted toward larger x, as the substrate temperature increased. The films were enriched in indium compared to the target composition and the cationic In/Zn ratio increased as the substrate temperature was increased. 相似文献
16.
(Bi1 − xSnx)2Te2.7Se0.3 thermoelectric thin films with thickness of 800 nm have been deposited on glass substrates by flash evaporation method at 473 K. The structures, morphology of the thin films were analyzed by X-ray diffraction and field emission scanning electron microscopy respectively. Effects of Sn-doping concentration on thermoelectric properties of the annealed thin films were investigated by room-temperature measurement of Seebeck coefficient and electrical resistivity. The thermoelectric power factor was enhanced to 12.8 μW/cmK2 (x = 0.003). From x = 0.004 to 0.01 Sn doping concentration, the Seebeck coefficients are positive and show p-type conduction. The Seebeck coefficient and electrical resistivity gradually decrease with increasing Sn doping concentration. 相似文献
17.
Deposition of Mn3CuNy thin films on single crystal Si (1 0 0) at various substrate temperatures (Tsub) by facing target magnetron sputtering is reported. The crystal structure and composition were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results confirmed that the crystalline antiperovskite Mn3CuNy thin film with (2 0 0) highly preferred texture had been obtained at Tsub = 180 °C. Furthermore, for the resulting Mn3CuNy thin film, it showed different properties compared with the bulk counterpart. There was a paramagnetic to ferrimagnetic transition at 225 K with decreasing temperature. The change of the lattice constant with temperature presented positive thermal expansion behavior and no structural transition was observed. The average linear thermal expansion coefficient (α) is 2.49 × 10−5 K−1 from 123 K to 298 K. More interestingly, the temperature dependence of resistivity displayed a semiconductor-like behavior, i.e. an obvious monotonous decrease of resistivity with increasing temperature. 相似文献
18.
We have carried out structural, magnetic and magneto transport measurements of the electron-doped manganite La0.3Ca0.7MnO3 substituted with 10% of Cr, Fe and W on the Mn site. The substitution by Cr, Fe and W suppresses the charge order transition present at 260 K in the parent compound. All the samples show a semiconducting behavior. Whereas the parent compound does not show any magneto resistance (MR) even in a field of 14 T, a maximum MR of 6% in 5 T at 25 K is observed for the Cr substituted sample that is attributed to a spin-cluster glass like states induced by Cr. The Fe and W substituted samples showed a MR of 1.5 and 3%, respectively which may be attributed to a smaller number of FM domains/spin-clusters and to an increase in anti-ferromagnetic interaction. 相似文献
19.
The effects of doping of MgAl2O4 by a binary mixture of Co and Zn ions on the absorbance, electrical resistivity, capacitance, thermal conductivity, heat capacity and thermal diffusivity are reported in this paper. The materials with the nominal composition Mg1−2x(Co,Zn)xAl2O4 (x = 0.0-0.5) are synthesized by solution combustion synthesis assisted by microwave irradiation. The substituted spinels are produced with a Scherrer crystallite size of 18-23 nm, as opposed to 45 nm for undoped samples, indicated by X-ray diffraction and confirmed by transmission electron microscopy. These materials also show better thermal stability in the temperature range of 298-1773 K. Three strong absorption bands at 536, 577 and 630 nm are observed for the doped samples which are attributed to the three spin allowed (4A2 (F) → 4T1 (P)) electronic transitions of Co2+ at tetrahedral lattice sites while pure magnesium aluminate remains transparent in the whole spectral range. The semiconducting behavior of the materials is evident from the temperature dependence of the electrical resistivity. Resistivity and activation energy are higher for the substituted samples. Fitting of the resistivity data is achieved according to the hopping polaron model of solids. Both dielectric constant and loss increase on account of doping. The dielectric data are explained on the basis of space charge polarization. The thermal conductivity and diffusivity are lowered and the heat capacity is increased in the doped materials. Wiedemann-Franz's law is used to compute the electronic and lattice contributions towards the total thermal conductivity. 相似文献
20.
Tae Eun HongKi-Yeung Mun Sang-Kyung ChoiJi-Yoon Park Soo-Hyun Kim Taehoon CheonWoo Kyoung Kim Byoung-Yong LimSunjung Kim 《Thin solid films》2012,520(19):6100-6105
Ruthenium (Ru) thin films were grown by atomic layer deposition using IMBCHRu [(η6-1-Isopropyl-4-MethylBenzene)(η4-CycloHexa-1,3-diene)Ruthenium(0)] as a precursor and a nitrogen-hydrogen mixture (N2/H2) plasma as a reactant, at the substrate temperature of 270 °C. In the wide range of the ratios of N2 and total gas flow rates (fN2/N2 + H2) from 0.12 to 0.70, pure Ru films with negligible nitrogen incorporation of 0.5 at.% were obtained, with resistivities ranging from ~ 20 to ~ 30 μΩ cm. A growth rate of 0.057 nm/cycle and negligible incubation cycle for the growth on SiO2 was observed, indicating the fast nucleation of Ru. The Ru films formed polycrystalline and columnar grain structures with a hexagonal-close-packed phase. Its resistivity was dependent on the crystallinity, which could be controlled by varying the deposition parameters such as plasma power and pulsing time. Cu was electroplated on a 10-nm-thick Ru film. Interestingly, it was found that the nitrogen could be incorporated into Ru at a higher reactant gas ratio of 0.86. The N-incorporated Ru film (~ 20 at.% of N) formed a nanocrystalline and non-columnar grain structure with the resistivity of ~ 340 μΩ cm. 相似文献