摘要 :
We have searched for time-reversal symmetry-breaking fields in the noncentrosymmetric superconductor Mg_(10)Ir_(19)B_(16) via muon spin relaxation (μSR) in zero applied field. We also measured the temperature dependence of the su...
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We have searched for time-reversal symmetry-breaking fields in the noncentrosymmetric superconductor Mg_(10)Ir_(19)B_(16) via muon spin relaxation (μSR) in zero applied field. We also measured the temperature dependence of the superfluid density by muon spin rotation in transverse field to investigate the superconducting pairing symmetry in two polycrystalline samples of significantly different purities. In the high-purity sample, we detected no time-reversal symmetry-breaking fields greater than 0.05 G. The superfluid density was also found to be exponentially flat as T→0 and so can be fit to a single-gap BCS model. In contrast, the lower purity sample showed an increase in the zero-field μSR relaxation rate below T_c corresponding to a characteristic field strength of 0.6 G. While the temperature dependence of the superfluid density was also found to be consistent with a single-gap BCS model, the magnitude as T→0 was found to be much lower for a given applied field than in the case of the high-purity sample. These findings suggest that Mg_(10)Ir_(19)B_(16) is a superconductor characterized by a single-gap function with no nodes and sample quality drastically affects the superconducting properties of this system.
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Thermal conductivity and mechanical effects of silicon carbide nanoparticles uniformly dispersed in water were investigated. Mean size of SiC particles was 170 nm with a polydispersity of -30% as determined from small-angle x-ray ...
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Thermal conductivity and mechanical effects of silicon carbide nanoparticles uniformly dispersed in water were investigated. Mean size of SiC particles was 170 nm with a polydispersity of -30% as determined from small-angle x-ray scattering and dynamic light scattering techniques. Room temperature viscosity of the nanofluids ranged from 2 to 3 cP for nominal nanoparticle loadings 4-7 vol %. On a normalized basis with water, viscosity of the nanofluids did not significantly change with the test temperature up to 85 ℃. Optical microscopy of diluted nanofluid showed no agglomeration of the nanoparticles. Thermal conductivity of the fluid was measured as a function of the nominal nanoparticle loading ranging from 1 to 7 vol %. Enhancement in thermal conductivity was approximately 28% over that of water at 7 vol % particle loadings under ambient conditions. Enhancements in thermal conductivities for the nanofluids with varying nanoparticle loadings were maintained at test temperatures up to 70 ℃. Results of thermal conductivity have been rationalized based on the existing theories of heat transfer in fluids. Implications of using this nanofluid for engineering cooling applications are discussed.
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A systematic study of the magnetic properties and the Hall effect was performed on pulsed laser deposited 5% cobalt doped (La,Sr)TiO_3 thin films, especially grown at high substrate temperature. The system is found to be superpara...
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A systematic study of the magnetic properties and the Hall effect was performed on pulsed laser deposited 5% cobalt doped (La,Sr)TiO_3 thin films, especially grown at high substrate temperature. The system is found to be superparamagnetic in nature as evidenced by several protocols of magnetic measurements. Nevertheless, the anomalous Hall effect (AHE) is observed in the system, the profile of the measured Hall resistivity vs magnetic field being found to be identical to the magnetic hysteresis loops. This highlights the limitations of AHE as a tool to test the intrinsic nature of ferromagnetism in a diluted magnetic system, supporting our previous report for the Co:TiO_2 case [S. R. Shinde et al, Phys. Rev. Lett. 92, 166601 (2004)]. It is believed that the magnetic clusters polarize nearby electrons and the nonzero polarization leads to a net transverse current because of the spin dependent scattering, which gives rise to the observed AHE. We found that the magnitude of the AHE signal observed in the current extrinsic diluted magnetic semiconductor (DMS) is much lower (by a few orders of magnitude) than that found in the intrinsic long range ferromagnetic ordered DMS, which raises the possibility for using this magnitude, rather than the occurrence of AHE, as a criterion for intrinsic or extrinsic diluted magnetic system.
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Zero-field (ZF) muon-spin-relaxation (μSR) measurements have revealed static commensurate magnetic order of Fe moments in NdFeAsO below T_N～ 135 K, with the ordered moment size nearly equal to that in LaFeAsO, and confirmed simi...
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Zero-field (ZF) muon-spin-relaxation (μSR) measurements have revealed static commensurate magnetic order of Fe moments in NdFeAsO below T_N～ 135 K, with the ordered moment size nearly equal to that in LaFeAsO, and confirmed similar behavior in BaFe_2As_2, In single crystals of superconducting Ba_(0.55)K_(0.45)Fe_2As_2, μSR spectra indicate static magnetism with incommensurate or short-ranged spin structure in ～70% of volume below T_N～80 K, coexisting with the remaining volume which exhibits a superfluid response below T_c～30 K.
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The combination of molecular-beam epitaxila (MBE) kgrwoth and in situ focused ion beam (FIB) technology, has attracted considerable research interest in rec3nt years since early studies in this area by Hirayama and Okamoto (Jpn. J...
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The combination of molecular-beam epitaxila (MBE) kgrwoth and in situ focused ion beam (FIB) technology, has attracted considerable research interest in rec3nt years since early studies in this area by Hirayama and Okamoto (Jpn. J. Appl. Phys. 24(1985) L965) and miyauchi et al. (J. Vac. Sci. Technol. B4 (1986) 189) on III-V semiconuctor material systems. In this paper, we describe a novel fabricaiton technqiue that directly integrates a FIB column into an MBE growth chamber. This "JFIMBE" system allows the generatoin of novel III-V kdevice sructures that would otherwise be impossible to fabricate via conventional lithographic techniques.
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摘要 :
Muon spin relaxation measurements in iron-oxypnictide systems have revealed: (1) commensurate long-range order in undoped LaFeAsO; (2) a Bessel function line shape in LaFeAs(O_(0.97)F_(0.03)) which indicates possible incommensurat...
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Muon spin relaxation measurements in iron-oxypnictide systems have revealed: (1) commensurate long-range order in undoped LaFeAsO; (2) a Bessel function line shape in LaFeAs(O_(0.97)F_(0.03)) which indicates possible incommensurate or stripe magnetism; (3) anomalous weak magnetism existing in superconducting LaFePO, CeFeAs(O_(0.084)F_(0.16)), and NdFeAs(O_(0.88)F_(0.12)) but absent in superconducting LaFeAs(O_(0.92)F_(0.08)); and (4) scaling of the superfluid density with T_c in the Ce-, La-, and Nd-FeAs superconductors following a nearly linear relationship found in cuprates.
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We report on the structural, electrical, and optical properties of 5% niobium doped TiO_2 thin films grown on various substrates by pulsed laser deposition. The epitaxial anatase Nb:TiO_2 film on LaAlO_3 is shown to be an intrinsi...
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We report on the structural, electrical, and optical properties of 5% niobium doped TiO_2 thin films grown on various substrates by pulsed laser deposition. The epitaxial anatase Nb:TiO_2 film on LaAlO_3 is shown to be an intrinsic transparent metal and its metallic property arises from Nb substitution into Ti site as evidenced by the Rutherford backscattering channeling result. In contrast, the rutile Nb: TiO_2 thin films show insulating behaviors with 2-3 orders higher room temperature electrical resistivity and ～30 times lower mobility. A blueshift in the optical absorption edge is observed in both phases, though of differing magnitude.
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摘要 :
A zinc oxide (ZnO) nanorod based surface acoustic wave (SAW) sensor has been developed and investigated towards hydrogen (H_2) gas. The ZnO nanorods were deposited onto a layered ZnO/64° YX LiNbO_3 substrate using a liquid soluti...
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A zinc oxide (ZnO) nanorod based surface acoustic wave (SAW) sensor has been developed and investigated towards hydrogen (H_2) gas. The ZnO nanorods were deposited onto a layered ZnO/64° YX LiNbO_3 substrate using a liquid solution method. Micro-characterization results revealed that the diameters of ZnO nanorods are around 100 and 40 nm on LiNbO_3 and Au (metallization for electrodes), respectively. The sensor was exposed to different concentrations of H_2 in synthetic air at operating temperatures between 200 ℃ and 300 ℃. The study showed that the sensor responded with highest frequency shift at 265 ℃. At this temperature, stable baseline and fast response and recovery were observed.
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