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In recent years, the Ni–Mo–Cr superalloy Hastelloy® C-276™ has been used as a substrate material for fabricating superconducting tapes such as YBCO and MgB2 coated conductors. With increasing piece length, these coated conductors are within reach of large scale commercial applications. However, data on the physical properties of Hastelloy C-276 at temperatures relevant for these applications are not yet available. In this work, physical properties including magnet succeptibility, specific heat, electrical resistivity, and the Seebeck coefficient are measured from 2 to 300 K and thermal conductivity from 2 to 200 K. Our results show that Hastelloy C-276 exhibits Curie paramagnetism between 4 and 300 K with a Curie constant C=0.091 K. A spin-glass-like behavior is observed below 3 K. The electrical resistivity has a minimum at ∼12 K, and shows a linear weak T dependence at higher temperatures. The specific heat Cp between 15 and 40 K follows Cp=γT+AT3. Below ∼10 K, an upturn in Cp/T with decreasing T is interpreted by the existence of very small ferromagnetic clusters. We found relatively strong phonon contribution to the thermal conductivity in the measured temperature range. In addition, we present the thermal diffusivity as a function of temperature calculated from the thermal conductivity and the Cp data. The Seebeck coefficient is found to be proportional to temperature. The results of our measurements provide important data not only for the specific applications of the superconducting coated conductors that use Hastelloy C-276 as substrates, but also for many other potential cryogenic temperature applications. [ABSTRACT FROM AUTHOR]

La[sub 0.67]Ca[sub 0.33]Mn[sub 1-χ]Cu[sub χ]O[sub 3] (χ = 0 and 0.15) epitaxial thin films were grown on the (100) LaAlO[sub 3] substrates, and the temperature dependence of their resistivity was measured in magnetic fields up to 12 T by a four-probe technique. We found that the competition between the ferromagnetic metallic (FM) and paramagnetic insulating (PI) phases plays an important role in the observed colossal magnetoresistance (CMR) effect. Based on a scenario that the doped manganites approximately consist of phase-separated FM and PI regions, a simple phenomenological model was proposed to describe the CMR effect. Using this model, we calculated the resistivity as functions of temperature and magnetic field. The model not only qualitatively accounts for some main features related to the CMR effect, but also quantitatively agrees with the experimental observations. [ABSTRACT FROM AUTHOR]

Dielectric measurements are used to characterize magnetic phase transitions in the doped ferroelectric oxides Ho1-xYxMnO3 (x=0–0.8). The focus of this study is on the effects of the magnetic field direction and Y doping on the reentrant T-B-θ phase diagrams below the Néel temperature. The response of Ho sublattice to the applied magnetic field plays a major role in all magnetic phase transitions for Y doping (x=0.0–0.8), consistent with previous results (x=0,0.6,0.8). Two successive Mn spin rotations in the ab plane in the antiferromagnetic state are driven by the exchange interaction with the Ho subsystem, through magnetodielectric coupling. Difference in energy between two ground Mn spin states is correlated with magnetic field induced perturbations in Ho lattice. The coupling between Ho and Mn can be explained by simple geometric relations of uniaxial anisotropy between magnetic field direction and c-axis of hexagonal HoMnO3. The magnetic field anisotropy study is an important step toward the understanding of magnetic and electric phase competition in the diluted Ho 4 f hexagonal system by the nonmagnetic ion yttrium (Y). [ABSTRACT FROM AUTHOR]

Dielectric measurements are used to characterize magnetic phase transitions in the doped ferroelectric oxides Ho1-xYxMnO3 (x=0–0.8). The focus of this study is on the effects of the magnetic field direction and Y doping on the reentrant T-B-θ phase diagrams below the Néel temperature. The response of Ho sublattice to the applied magnetic field plays a major role in all magnetic phase transitions for Y doping (x=0.0–0.8), consistent with previous results (x=0,0.6,0.8). Two successive Mn spin rotations in the ab plane in the antiferromagnetic state are driven by the exchange interaction with the Ho subsystem, through magnetodielectric coupling. Difference in energy between two ground Mn spin states is correlated with magnetic field induced perturbations in Ho lattice. The coupling between Ho and Mn can be explained by simple geometric relations of uniaxial anisotropy between magnetic field direction and c-axis of hexagonal HoMnO3. The magnetic field anisotropy study is an important step toward the understanding of magnetic and electric phase competition in the diluted Ho 4 f hexagonal system by the nonmagnetic ion yttrium (Y). [ABSTRACT FROM AUTHOR]

Dielectric measurements are used to characterize magnetic phase transitions in the doped ferroelectric oxides Ho1-xYxMnO3 (x=0.4). The focus of this experiment is on the effects of the magnetic field direction on the reentrant T-B-θ phase diagram below the Néel temperature. The Ho sublattice plays a major role in all magnetic phase transitions for Y doping (x=0.4), consistent with previous results (x=0,0.6,0.8). Two successive Mn spin rotations in the ab plane in the antiferromagnetic state are driven by the interaction with the Ho subsystem, although the Ho ordering peak in data is not pronounced. The dielectric response is a very sensitive probe for fine analysis of all aspects of spin-spin interactions in diluted Ho1-xYxMnO3. The magnetic field anisotropy study is an important step towards the understanding of magnetic and electric phase competition in the diluted 4f system by the nonmagnetic yttrium (Y) ion. [ABSTRACT FROM AUTHOR]

We present the frequency dependence of microwave-absorbing properties of La[sub 1-x]Sr[sub x]MnO[sub 3] (x=0.4, 0.5, 0.6, and 0.7) powders at room temperature. The absorbing properties change gradually with x in the frequency range of 8–12 GHz. The optimal absorption can be achieved for a x=0.4 sample and its microwave loss peak value is about 25 dB. Further experimental results show that the absorption can be attributed to magnetic and dielectric losses and the microwave loss peak corresponds to the maximum dielectric loss tangent tan δ[sub e] near 10.5 GHz. Furthermore, the absorbing properties of the oxides mixed with carbonic fiber and Y-type planar hexagonal ferrite have been rudimentarily studied. Results show that these additives greatly enhance the microwave-absorbing properties of the oxides. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]