Why non-superconducting metallic elements become superconducting under high pressure

We predict that simple metals and early transition metals that become superconducting under high pressures will show a change in sign of their Hall coefficient from negative to positive under pressure. If verified, this will strongly suggest that hole carriers play a fundamental role in `conventional' superconductivity, as predicted by the theory of hole superconductivity.Comment: Submitted to M2S-IX Tokyo 200

Rapid cooling methods for pulsed magnets

Pulsed magnets are generally evaluated and compared in terms of the magnetic field they can achieve in combination with a bore size. However, in practice another criterion is equally important: the waiting time for a researcher in between two consecutive shots. The cooling time of pulsed magnets can range from a few minutes up to several hours, depending on coil size and desired field. Using simulations and measurements several options to reduce the cool down time are compared in this paper. One of the discussed methods is now routinely in use at the Laboratoire National des Champs Magnetiques Pulses (LNCMP) in Toulouse

Fabrication of Fischer-Tropsch Catalysts by Deposition of Iron Nanocrystals on Carbon Nanotubes

The fabrication of supported catalysts consisting of colloidal iron oxide nanocrystals with tunable size, geometry, and loadinghomogeneously dispersed on carbon nanotube (CNT) supportsis described herein. The catalyst synthesis is performed in a two-step approach. First, colloidal iron and iron oxide nanocrystals with a narrow size distribution are produced. Second, the nanocrystals are attached to CNT grains serving as support structure. Important features, like iron loading and nanocrystal density on the CNT support, are controlled by changing the nanocrystal concentration and ligand concentration, respectively. The Fischer-Tropsch performance reveals these new materials to be active, selective toward lower olefins (60% C of hydrocarbons produced in the absence of promoters), and remarkably stable against particle growth

Ni/Pd@MIL-101: Synergistic Catalysis with Cavity-Conform Ni/Pd Nanoparticles

Deutsche Forschungsgemeinschaft [SFB 840]Deutsche Forschungsgemeinschaf

Kernmagnetische Ordnung und Supraleitung in Metallen mit starker Hyperfeinwechselwirkung und elektronische magnetische Ordnung in Schwere-Fermionen-Verbindungen Schlussbericht

We have investigated the magnetic and superconducting groundstates of highly pure Pt powder, Sn, PrBi, and CeCu_6 by means of the electrical resistivity, magnetic ac susceptibility, heat capacity, and neutron diffraction experiments. Surprisingly, in compacts made of highly pure Pt powder of micrometer grain size we have found superconductivity, which has not been observed in bulk Pt before. In the superconducting nuclear paramagnet Sn we have observed a reduction of the superconducting critical field B_c(T) which is proportional to the nuclear magnetization, as already observed for Al. In addition, small jumps in the B_c(T) curve of Sn seem to occur at T < 6 mK which have not been observed in any material before. As in the first period of our project in PrS (T_N=90 #mu#K), we have observed a spontaneous nuclear antiferromagnetic ordering transition in thermodynamic equilibrium in the cubic Van Vleck paramagnet PrBi(T_N=1.2 mK). Due to its comparably 'high' ordering temperature and its small neutron absorption, the hyperfine enhanced nuclear antiferromagnet PrBi is an interesting candidate for neutron diffraction experiments in future. The data of heat capacity and neutron diffraction taken on the heavy fermion compound CeCu_6 yield further hints for a correlated magnetic ground state of small Ce moments. (orig.)Durch Messung des elektrischen Widerstandes, der magnetischen Wechselfeldsuszeptibilitaet, der Waermekapazitaet und der Neutronenstreuung bei ultratiefen Temperaturen haben wir die magnetischen und supraleitenden Grundzustaende von hochreinem Pt-Pulver, Sn, PrBi und CeCu_6 untersucht. In kompaktierten Proben aus hochreinem mikrogranularem Pt-Pulver konnten wir ueberraschenderweise Supraleitung nachweisen, die in massivem Pt bislang noch nicht festgestellt werden konnte. Im supraleitenden Kemparamagneten Sn fanden wir wie bereits frueher in Al eine zur Kernmagnetisierung proportionale Reduktion des supraleitenden kritischen Feldes B_c(T)-Kurve bei Temperaturen T < 6 mK aufzutreten. Im kubischen Van Vleck-Paramagneten PrBi(T_N=1.2 mK) konnten wir zuletzt, wie bereits in der ersten Foerderperiode am PrS (T_N-90 #mu#K), spontane kernantiferromagnetische Ordnung im thermodynamischen Gleichgewicht beobachten. Aufgrund seiner vergleichsweise 'hohen' Ordnungstemperatur und seiner geringen Neutronenabsorption ist der hyperfeinverstaerkte Kernantiferromagnet PrBi ein interessanter Kandidat fuer zukuenftige Neutronenstreuuntersuchungen. Die an der Schwere-Fermionen-Verbindung CeCu_6 ermittelten Waermekapazitaets- und Neutronenstreudaten geben weitere Hinweise auf einen magnetisch korrelierten Grundzustand kleiner Ce-Momente. (orig.)SIGLEAvailable from TIB Hannover: DtF QN1(98,46) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman