We have systyematically studied the thermal conductivity of the quaternary nickel borocarbide compounds Rni2B2C(R=Gd, Dy, Ho, Er, Tm and Lu). Thermal conductivity measurements have been conducted for Rni2B2C systems in the temperature range from 4.2K to 25K, under applied magnetic fields up to 30 kOe. The temperature dependence of thermal conductivity for the superconducting samples in zero magnetic fields show small and clear decrease at their superconducting transition temperatures. In zero or lower magnetic fields, the thermal conductivity for the samples with magnetic transition show small peak at their magnetic transition temperatures (TN or TM), which disappear under higher applied magnetic fields, The results suggest the existence of strong electron-phonon interplay in these compounds.

Applied magnetic field dependence of thermal conductivity (TC) and the temperature dependences of resistivity and magnetization on the nickel borocarbide superconducting compound LuNi2B2C have been measured in the temperature range from 4.2 to 30K, under the applied magnetic field range of 0-8T. The magnetic field dependence of the TC showed characteristic behavior at the lower and the upper critical fields at temperatures below Tc. We present the first temperature dependence curve of upper critical field derived from the results of TC measurement of LuNi2B2C.

The YBa2Cu3-xNixO7-δ with x=0-0. 4 have been studied using positron annihilation technique. The changes of positron annihilation parameters with the Ni substitution concentration x are given. From the change of electronic density ne and Tc, it would prove that the localized carriers (electron and hole) in Cu-O chain and CuO2 planes have enormous influence on superconductivity by affecting charge transfer between the reservoir layer and CuO2 planes.

The dependence of magnetic properties on lattice constants in both body-centered-cubic (bcc) and facecentered-cubic (fcc) FexMn1-x (x=0, 0.25,0.5,0.75,1) has been studied systematically using first-principles linearized augmented plane-wave (LAPW) calculations. The results indicate that the magnetic properties of bcc FexMn1-x alloys are ferromagnetism within a fairly large range of lattice constants, and the atomic moment increases with an increase of the lattice constants. However, for fcc FexMn1-x alloys, the magnetic properties change from paramagnetism to antiferromagnetism (or ferrimagnetism) and finally to ferromagnetism with an increase of the lattice constants. The calculated magnetic moment is consistent with previous experiments for bcc FexMn1-x alloys at the normal lattice constants, while for fcc FexMn1-x alloys on the whole the magnetic properties are also in agreement with the experimental results. The present results may facilitate a better understanding of the correlation between the structures and the corresponding magnetic properties.

To clarify the suppressing mechanism of Zn and Al substitution on high-Tc superconductivity, positron annihilation experiment and simulated calculation are used to study systemically the YBa2Cu3−x(Zn, Al)xO7-δ(x=0.0–0.4) cuprates. The results show that Zn doping ions prefer to combine into the cluster of seven ions with a double square and Al doping ions prefer to form six-ion-cluster with a hexamer structure, respectively. These clusters, especially for Zn, would evidently influence the positron annihilation characteristics, which can be seen from the variation of ne with Zn content x in the clustering process. ne displays an abrupt change as the impurity phases appear in both Zn and Al doping systems. From the doping process, Zn ions occupy Cu(2) sites in the CuO2 planes and make the change of electron structure, resulting in the carrier localization. As a result, it interferes the pairing and transportation of superconducting carriers and then suppresses the superconductivity with the formation of Zn clusters. While Al ions enter Cu(1) sites in the Cu-O chains, they induce the localization of hole carriers and weaken the function of carrier reservoir by forming clusters. Therefore, the carriers cannot easily transfer to the CuO2 planes. Since Al doping does not affect the pairing and transportation directly, it suppresses the superconductivity weakly than Zn doping. The effect of pairing and transportation of carriers on charge transfer is also discussed.