S. Matas

Magnetic and transport properties of U1−xCexRu2Si2

Abstract Pseudoternary compounds of the heavy fermion series U 1− x Ce x Ru 2 Si 2 ( x ⩽0.1 and x ⩾0.9) have been characterized by means of electrical resistivity and magnetic susceptibility measurements. High field magnetization measurements revealed an increase of the metamagnetic-like transition field of CeRu 2 Si 2 by allowing with U, and a suppression of the three-step magnetization process in URu 2 Si 2 by alloying with Ce. The influence of chemical pressure is investigated.

Influence of residual phases on the properties of YBa/sub 2/Cu/sub 2/O/sub 7-x/

The partial melting in YBaCuO incompletely synthesised powders occurring at temperatures below the peritectic decomposition of the 123 (i.e. YBa/sub 2/Cu/sub 3/O/sub 7-x/) compounds is related to the presence of residual phases. Our results showed that the final ceramic has a high porosity, which is independent of the temperature of sintering, the double grain size distribution and two transition temperatures up to the sintering temperature (940/spl deg/C) as a consequence of a higher content of the residual carbonate. Sintering at a higher temperature improved the superconducting properties of our ceramics. This progress is connected with the cracking of large grain ceramics and with the decomposition of carbonate BaCO/sub 3/. >

Neutron Scattering Experiment on Solid 3He

Magnetic neutron scattering probes the order parameter symmetry and magnitude on the atomic length scale, as well as exchange parameters in a critical scattering experiment above the ordering temperature. Therefore we propose an experiment for magnetic neutron diffraction on solid 3He. Difficulties arise from heat input and small signal intensities, both due to neutron absorption. Thus, a special design of neutron spectrometer, sample cell, and cryostat is required. We present calculated requirements of the involved components. We show the feasibility and possibilities of such an experiment along with first results of performance measurements of some of the parts.

Susceptibility and specific heat of CeRu/sub 2/Si/sub 2/ doped with U

The susceptibility, /spl chi/, and the specific-heat, C/sub p/, have been measured on the pseudo-ternary compounds Ce/sub 1-x/U/sub x/Ru/sub 2/Si/sub 2/ (0/spl les/x/spl les/0.1). The measurements were taken on single crystals. We have found an increase of antiferromagnetic correlations, as it is evident from susceptibility measurements, and a decrease of the electronic specific-heat coefficient /spl gammasub T/spl rarr/0/ with the U alloying of CeRu/sub 2/Si/sub 2/. We did not find any evidence of a long-range magnetic ordering. The estimated changes of susceptibility and heat-capacity were discussed in the frame of volume changes due to the alloying of CeRu/sub 2/Si/sub 2/. >

Effect of Ce substitution on antiferromagnetic transition in the heavy-electron compound URu/sub 2/Si/sub 2/

The effect of Ce substitution for U in the heavy-electron system URu/sub 2/Si/sub 2/, has been investigated by means of susceptibility, resistivity and specific-heat measurements. Our measurements taken on single-crystalline samples indicate that a spin-density-wave transition at 17.5 K is rapidly suppressed with alloying. The Neel temperature initially falls but then recovers as 5% substitution is approached. The strong magnetocrystalline anisotropy changes from uniaxial type to multiaxial type for x=0.05. The anomalies in the susceptibility, resistivity and specific-heat below 30 K suggest the presents of another type of magnetic ordering which is quite different from that of URu/sub 2/Si/sub 2/. >

Influence of neutron and proton irradiation on inter- and intragrain properties of BiPbCaSrCuO ceramics

The influence of irradiation by fast neutrons and protons (1.4×1014 n/cm2 and 1.6×1014 p/cm2) on the physical properties of textured Bi1.85Pb0.35Sr1.9Ca2.09Cu3.05Oy was examined. DC magnetization in low and high magnetic field are performed. No influence of irradiation on Tc and intragranular properties was observed. The decoupling of weak links with irradiation was observed in low field magnetization measurements. The magnetic behaviour was found to be anizotropic by a factor about 2.5 and this factor was not affected by irradiation.

Phases interaction and properties of [Bi/sub 2/Sr/sub 2/Cu/sub 1/O/sub 6/]/sub 1-z/-[BiOF]/sub z/ system

The [Bi/sub 2/Sr/sub 2/Cu/sub 1/O/sub 6/]/sub 1-z/-[BiOF]/sub z/ solid solutions were prepared by an original many steps solid state reaction method. X-ray studies of samples with different fluorine concentration were carried out. Concentration dependencies of enthalpy, melting temperature and mass change during melting process were studied by DTA method. The influence of starting composition (namely fluorine concentration) on changes in microstructure, crystallographic parameters and melting character was investigated. >

Gamma-rays irradiation of YBaCuO

A YBa/sub 2/Cu/sub 3/O/sub 7-x/ ceramic was sequentially irradiated with /sup 60/Co /spl gamma/-rays of 155.4 R/min in dose rate; up to the dose 5000 Gy at ambient temperature, AC susceptibility and magnetization were measured as a function of temperature and magnetic field, respectively. The transition to the superconducting state has decreased roughly linearly with radiation dose at a rate of 6.2*10/sup -4/ K/Gy probably as a consequence of the change of carrier concentration in CuO/sub 2/ planes. The intragrain critical current density has increased for lower and higher radiation doses. Formation of the extra centres of pinning by /spl gamma/ irradiation is suggested. >