Investigation of non-magnetic iron in Lu2Fe3Si5-type superconductors

A focussed study on the effect of transition metal substitution for Fe in the compounds Lu[subscript]2(Fe[subscript]1-xT[subscript]x)[subscript]3Si[subscript]5 (Where T = Cr, Mn, Co, Ni Cu, and Ru) is reported. The effect of these transition metals on the superconducting transition temperature shows that Cr, Co, Ni and Ru all act as non-magnetic impurities. By fitting the experimental data T[subscript]c/T[subscript]co to Kaiser\u27s equation, a good agreement with Kaiser\u27s theory is obtained. The rate of suppression due to Co substitution is similar to that of Ru. Superconductivity persists ( T[subscript]c = 0.49K) even when 10 at.% Co is substituted for Fe. In contrast, Mn and Cu act as magnetic impurities and suppress T[subscript]c in a way described by the theory of Abrikosov and Gor\u27kov;The molar magnetic susceptibility of Lu[subscript]2Fe[subscript]3Si[subscript]5 does not follow a Curie-Weiss law, but rather increases slightly as temperature increases. The addition of Ru lowers the value of [chi] (T), but the overall shape of [chi] (T) is unchanged. In contrast, the substitution of the nominally magnetic transition metals Cr, Mn, Co and Ni for Fe causes [chi] (T) to become more Curie-Weiss like. The magnetic susceptibility of the compound Lu[subscript]2Co[subscript]3Si[subscript]5 follows the Curie-Weiss law, while that of the compound Lu[subscript]2Ru[subscript]3Si[subscript]5 is diamagnetic;The electrical resistivity [rho] (T) of the compound Lu[subscript]2Fe[subscript]3Si[subscript]5 is approximately quadratic in T at temperatures below 50 K and proportional to lnT at temperature above 100 K;The low temperature heat capacity data of the Co- and Ru-containing samples are similar and both fit to equations [gamma][subscript]sT+[beta][subscript]sT[superscript]3 below T[subscript]c and [gamma][subscript]nT+[beta][subscript]nT[superscript]3+[alpha][subscript]nT[superscript]5 above T[subscript]c in agreement with the heat capacity measurement by C. B. Vining for the compound Lu[subscript]2Fe[subscript]3Si[subscript]5. Increasing the concentration of Co or Ru lowers the Debye temperature and the electronic density of states at the Fermi level of the compounds and enhances the linear term in the superconducting state heat capacity. The reduced specific heat jump between C[subscript]s and C[subscript]n at T[subscript]c follows neither the BCS prediction nor the Abrikosov and Gor\u27kov\u27s theory;All of the data in this investigation show that the strong covalent bonding between the iron and the silicon atoms in this complex crystal structure is related directly to the unusual behavior of these 3d transition metals in the compounds Lu[subscript]2(Fe[subscript]1-xT[subscript]x)[subscript]3Si[subscript]5. ftn * DOE Report IS-T-1280. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy

Residual donors and compensation in metalorganic chemical vapor deposition as-grown n-GaN

In our recent report, [Xu et al., Appl. Phys. Lett. 76, 152 (2000)], profile distributions of five elements in the GaN/sapphire system have been obtained using secondary ion-mass spectroscopy. The results suggested that a thin degenerate n+ layer at the interface is the main source of the n-type conductivity for the whole film. The further studies in this article show that this n+ conductivity is not only from the contribution of nitride-site oxygen (ON), but also from the gallium-site silicon (SiGa) donors, with activation energies 2 meV (for ON) and 42 meV (for SiGa), respectively. On the other hand, Al incorporated on the Ga sublattice reduces the concentration of compensating Ga-vacancy acceptors. The two-donor two-layer conduction, including Hall carrier concentration and mobility, has been modeled by separating the GaN film into a thin interface layer and a main bulk layer of the GaN film. The bulk layer conductivity is to be found mainly from a near-surface thin layer and is temperature dependent. SiGa and ON should also be shallow donors and VGa-O or VGa-Al should be compensation sites in the bulk layer. The best fits for the Hall mobility and the Hall concentration in the bulk layer were obtained by taking the acceptor concentration NA=1.8×1017 cm-3, the second donor concentration ND2=1.0×1018 cm-3, and the compensation ratio C=NA/ND1=0.6, which is consistent with Rode's theory. Saturation of carriers and the low value of carrier mobility at low temperature can also be well explained. © 2001 American Institute of Physics.published_or_final_versio

Evaluation of [11C]metergoline as a PET Radiotracer for 5HTR in Nonhuman Primates

Metergoline, a serotonin receptor antagonist, was labeled with carbon-11 in order to evaluate its pharmacokinetics and distribution in non-human primates using positron emission tomography. [11C]Metergoline had moderate brain uptake and exhibited heterogeneous specific binding, which was blocked by pretreatment with metergoline and altanserin throughout the cortex. Non-specific binding and insensitivity to changes in synaptic serotonin limit its potential as a PET radiotracer. However, the characterization of [11C]metergoline pharmacokinetics and binding in the brain and peripheral organs using PET improves our understanding of metergoline drug pharmacology.Chemistry and Chemical Biolog

Irreversibility temperatures in oxide- and metallic superconductors

We measured the irreversibility temperatures, T{sub r}(H) for both oxides (pure and alloyed Y(123) and Bi(2212, 2223)) and metallic (Nb, NbTi, and Nb{sub 3}Sn) superconductors. These results are compared and discussed in terms of T{sub r}(H) being the depinning line and/or the melting line of the flux line (crystalline or disordered) lattice in the H-T plane

Modelling of plasma response to 3D external magnetic field perturbations in EAST

Sustained mitigation and/or suppression of type-I edge localized modes (ELMs) has been achieved in EAST high-confinement plasmas, utilizing the resonant magnetic perturbation (RMP) fields produced by two rows of magnetic coils located just inside the vacuum vessel. Systematic toroidal modelling of the plasma response to these RMP fields with various coil configurations (with dominant toroidal mode number n = 1, 2, 3, 4) in EAST is, for the first time, carried out by using the MARS-F code (Liu et al 2000 Phys. Plasmas 7 3681), with results reported here. In particular, the plasma response is computed with varying coil phasing (the toroidal phase difference of the coil currents) between the upper and lower rows of coils, from 0 to 360°. Four figures of merit, constructed based on the MARS-F computations, are used to determine the optimal coil phasing. The modelled results, taking into account the plasma response, agree well with the experimental observations in terms of the coil phasing for both the mitigated and the suppressed ELM cases in EAST experiments. This study provides a crucial confirmation of the role of the plasma edge peeling response in ELM control, complementing similar studies carried out for other tokamak devices

Model of defect formation in annealed undoped and Fe-doped liquid encapsulated Czochralski InP

Infrared absorption spectroscopy measurements indicate high concentration of hydrogen indium vacancy complex VInH4 in undoped and Fe-doped liquid encapsulated Czochralski (LEC) InP. Annealed undoped and Fe-doped semi-insulating (SI) InP are studied by room temperature Hall effect measurement and photocurrent spectroscopy. The results show that a mid gap donor defect and some shallow intrinsic defects are formed by high temperature annealing. This mid gap defect is shown to be phosphorus antisite related. Defect formation process and compensation mechanism in annealed SI InP are discussed.published_or_final_versio

ELM control with RMP: Plasma response models and the role of edge peeling response

Resonant magnetic perturbations (RMP) have extensively been demonstrated as a plausible technique for mitigating or suppressing large edge localized modes (ELMs). Associated with this is a substantial amount of theory and modelling efforts during recent years. Various models describing the plasma response to the RMP fields have been proposed in the literature, and are briefly reviewed in this work. Despite their simplicity, linear response models can provide alternative criteria, than the vacuum field based criteria, for guiding the choice of the coil configurations to achieve the best control of ELMs. The role of the edge peeling response to the RMP fields is illustrated as a key indicator for the ELM mitigation in low collisionality plasmas, in various tokamak devices