On the Tc of dilute alloys

The equation for the critical temperature T_c, of a dilute superconducting alloy due to Markowitz and Kadanoff (MK) is generalized to include renormalization effects due to the electron-phonon interaction. Such corrections constitute a 50% effect in weak coupling superconductors like aluminum while in strong coupling systems like lead this correction gives a factor of 2.5. The mean square anisotropy parameter appearing in the T_c equation is also generalized to remove the separability assumption of the electron-phonon interaction. Some consequences of these two corrections to the analysis and systematization of data for dilute superconducting alloys is discussed.     

Superconductivity and magnetism in Ir-doped GdFeAsO

The 5d-transition metal, Ir has successfully been doped at Fe site and induced superconductivity in GdFeAsO at T_c = 18.9 K and ∼20 atom%. The Ir-doping shortened the c-axis length and stretched the a-axis one, which led to enhance the coupling between the FeAs- and SmO-layer, and to weaken the bonding between Fe and As atom. Paramagnetism was observed in all of the samples, which was resulted from the magnetic Gd ion as in the F-doped GdFeAsO. An upper critical field of GdFe_0.8Ir_0.2AsO was extrapolated to around 24 T, much smaller than that of F-doped GdFeAsO owing to a relatively low T_c and small value of dH_c2/dT.     

Superconductivity and magnetism in HoNi2B2C

The effect of magnetic ordering on superconductivity in HoNi₂B₂C is studied. It is concluded that the abrupt suppression of superconductivity in the region of incommensurate antiferromagnetic ordering is due to a modification of the wave functions of the conduction electrons by the long-range magnetic order. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 9, 702–707 (10 May 1996)     

Flux States,Anyons and High Tc Superconductivity

In this paper, we studied the statistical behavior of anyons with isospin degrees of freedom, in which the fluctuation of isospjn degrees of freedom satisfies the O(3) nonlinear σ model. Under the mean field treatment, this model is in somewhat equivalent to the doped or frustrated Heisenberg an tiferromagnetic (AFM) model. We also studied the relation between the statistical field A_μ, and Skyrmion current B_μ. Finally, we set up the relation between flux states and spinon statistics, and the conditions of Bose condensation of holons. In particular, for π-flux state of A_μ, the spinons are bosons, the holons satisfy 2/3 fractional statistics.     

Superconductivity and field-induced magnetism in Pr2-xCexCuO4 single crystals

We report muon-spin rotation and relaxation (muSR) measurements on single crystals of the electron-doped high-T(c) superconductor Pr2-xCexCuO4. In a zero external magnetic field, superconductivity is found to coexist with dilute Cu spins that are static on the muSR time scale. In an applied field, we observe a mu(+)-Knight shift that is primarily due to the magnetic moment induced on the Pr ions. Below the superconducting transition temperature T(c), an additional source of local magnetic field appears throughout the volume of the sample. This finding is shown to be consistent with field-induced antiferromagnetic ordering of the Cu spins. Measurements of the temperature dependence of the in-plane magnetic penetration depth lambda(ab) in the vortex state are also presented.     

Impurity-impurity interactions in dilute alloys

The interaction between impurities of two solute elements in metal hosts leads to a non-random distribution of impurity atoms among the lattice sites. Experimental studies of this distribution provide quantitative information on the energy involved in the formation of an individual impurity-impurity pair. It is shown how this energy can be extracted from PAC and Mössbauer spectra. A review of the experimental results for several metallic matrices is given. The binding energy of the impurity-impurity pairs is discussed in terms of a correlation with the heat of formation for corresponding alloys.     

Superconductivity,magnetism and metastability of new ternary iridium borides

Superconductivity has been found in the rare earth iridium borides with the general formula MIr₄B₄ and in the pseudoternary (Y_xLu_1?x)?Ir₄B₄ system, M being a rare earth element. The pure phase in itself is only metastable at best. The compounds were found to crystallize with the primitive tetragonal CeCo₄B₄-type structure. The close correlation between superconductivity, magnetism and structural metastability is demonstrated with the study of the pseudoternary systems M(Ir_xRh_1?x)₄B₄ (x = 0.1 and 0.5) and Er(Ir_xRh_1?x)₄B₄.     

Superconductivity and magnetic susceptibility of TiU alloys

The superconducting transition temperatures of $\text{TiU}$ alloys have been measured. They peak at a temperature of 3.8 K at 20 a/o U. Similar behavior is seen for $\text{Ti}$Cr, $\text{Ti}$Mo, and $\text{Ti}$W indicating that U in Ti behaves like a hexavalent transition metal and is not magnetic. Magnetic susceptibility measurements support this viewpoint.     

Superconductivity and resistivity of amorphous niobium-germanium alloys

The superconducting transition temperature, T_c, and the normal state resistivity, π, for amorphous niobium-germanium alloys were shown to vary smoothly with composition. Most notably, no anomaly was observed in the amorphous state at the composition Nb₃Ge.     

Interstitialcy diffusion in B. C. C. metals and dilute alloys

The fundamental processes whose knowledge is necessary to the understanding of interstitialcy diffusion in bcc—as compared to fee—lattices are discussed. A major difference is that there is no possible cage effect for mixed <IIO> dumbbells in bee lattices, whatever the jump mechanism (with or without rotation) may be. Besides, jumps without rotation are favoured in bee's as compared to fee's. For these two reasons, long range diffusion of solute atoms apt to form mixed interstitials, by an interstitialcy mechanism, that is at low temperature, should be greatly favoured in bcc lattices.     

Magnetoelastic effects in dilute magnetic alloys

Ultrasonic studies of $\text{Cu}$Mn, $\text{Au}$Mn and $\text{Au}$Fe alloys where the concentrations of the transition metal ranges between 1 and 10% show that the longitudinal sound velocity has a marked field dependence at temperatures below the peak in the magnetic susceptibility and a negligible field dependence above it. This suggests that there may be an ordered magnetic state in these alloys.     

Atomic displacements in bcc dilute alloys

We present here a systematic investigation of the atomic displacements in bcc transition metal (TM) dilute alloys. We have calculated the atomic displacements in bcc (V, Cr, Fe, Nb, Mo, Ta and W) transition metals (TMs) due to 3d, 4d and 5d TMs at the substitutional site using the Kanzaki lattice static method. Wills and Harrison interatomic potential is used to calculate the atomic force constants, the dynamical matrix and the impurity-induced forces. We have thoroughly investigated the atomic displacements using impurities from 3d, 4d and 5d series in the same host metal and the same impurity in different hosts. We have observed a systematic pattern in the atomic displacements for Cr-, Fe-, Nb-, Mo-, Ta-and W-based dilute alloys. The atomic displacements are found to increase with increase in the number of d electrons for all alloys considered except for V dilute alloys. The 3d impurities are found to be more easily dissolved in the 3d host metals than 4d or 5d TMs whereas 4d and 5d impurities show more solubility in 4d and 5d TMs. In general, the relaxation energy calculation suggests that impurities may be easily solvable in 5d TM hosts when compared to 3d or 4d TMs.