On the addition of silver to highT c (Y1Ba2Cu3O7−x ) superconductor

The superconducting transition temperature of the highT _c compound Y₁Ba₂Cu₃O_7−x does not show degradation consequent upon the addition of metallic silver up to a concentration of 60 wt per cent. The X-ray diffraction data confirm that the oxygen deficient distorted orthorhombic perovskite structure of the pure compound stays intact as if silver does not enter the crystal lattice. SEM studies do show the presence of silver at the grain boundaries only. Silver is found to restrict the grain growth.     

Hyperfine fields at sp sites in Clb Heusler alloys

Hyperfine fields have been measured at Cd, Sn and Sb sites in several Ni, Rh, Ir and Pt-based Heusler alloys. The Cd fields at 77 K were found to be ?95 k0e, ?108(4) k04, ±166(5) k0e and +196(9) k0e in RhMnSb, IrMnSn, IrMnSb and PtMnGa, respectively. Sn-site fields were found to be ±53(5) k0e and ±62(5) k0e in NiMnSb and PtMnSb, respectively, and the Sb-site fields, +276(5) k0e, +65(5) k0e and +210(5) k0e in NiMnSb, IrMnSb and PtMnSb, respectively. Results are discussed in terms of 5sp site hyperfine field systematics in Cl_b Heusler alloys.     

Trapping energy of a magnetic monopole in magnetic materials

Analytical methods to investigate the interaction of magnetic monopoles with known magnetic media have been developed. Trapping energies of monopoles inside ferro-magnetic or super onducting materials of size greater than about 10⁻⁶ cm are found to be of the order of several kiloelectron volts. These are two to three orders of magnitude higher than in paramagnetic materials. Thus if stable magnetic monopoles exist at all in the universe, they are perhaps trapped in these magnetic materials. The effect of the finite size of the magnetic bodies is taken into account explicitly in our calculations of the trapping energy.     

Low concentration of the superconducting phase and thermoelectric power in 90 K superconductors

The thermoelectrical power (TEP) and the electrical resistivity behaviour of three 90 K superconductors viz, Y₁Ba₂Cu₃O_7−x , Sm₁Ba₂Cu₃O_7−x and Gd₁Ba₂Cu₃O_7−x , after the specimens were quenched from the sintering temperature (920°C) to 77 K, are reported. Interestingly the Y₁₂₃ specimen, which has the presence of trace amount of the orthorhombic phase in an otherwise tetragonal phase and does not show a superconducting transition down to 77 K shows zero TEP around 82 K, theT _c for the well oxygenated specimen. The Sm and Gd specimens on the other hand show completely tetragonal structure, semiconducting behaviour in resistivity and no zero TEP up to 77 K. It is argued that the critical concentration of the superconducting phase necessary to make the TEP zero is much smaller than that required for zero resistivity.     

Synthesis,spectroscopic and antifungal studies of transition metal trinuclear/polynuclear complexes with azolo-2,4-pentanedione: Part III

Azolo (thiazolo and triazolo)-2,4-pentanedione (L1 and L2) were condensed with o-phenylenediamine in the presence of the chloride salts of nickel(II), copper(II) and palladium(II). The resulting trinuclear/polynuclear complexes were characterized by elemental analysis, conductance and magnetic moments (room temperature and variable temperature) as well as i.r., u.v.–vis., 1H-n.m.r. and e.s.r. spectra.     

A characterisation of spreads ovally-derived from Desarguesian spreads

We characterise all spreads that are obtainable from Desarguesian spreads by replacing a partial spread consisting of translation ovals; the corresponding ovally-derived planes are generalised André planes, of order 2 ^N , although not all generalised André planes are ovallyderived from Desarguesian planes. Our analysis allows us to obtain a complete classification of all nearfield planes that are ovally-derived from Desarguesian planes. It turns out that whether or not a nearfield plane is ovally-derived from a Desarguesian plane depends solely on the parametersq andr, where GF (q) is the kern, andr is the dimension of the plane. Our results also imply that a Hall plane of even orderq ² can be ovally-derived from a Desarguesian spread if and only ifq is a square.