Normal-state anomalies in the transport and magnetic properties in the (La1-xPrx)(1.85)Sr0.15CuO4 system and their correlation with T-c suppression: A signature of the effects of orthorhombic distortions

The correlation between the normal-state anomalies observed in the magnetic and transport properties of the (La1-xPrx)(1.85)SR0.15CUO4 system with 0 less than or equal to x less than or equal to 0.5 was studied. The x-ray-diffraction patterns revealed a linear increase of the (a-b) orthorhombic parameter with the Pr content. The resistivity curves showed an increasing deviation from linearity below similar to 100 K. This anomaly was properly accounted by a logarithmic term, whose coefficient C linearly increases with x. Superconducting quantum interference device measurements of the normal-state magnetic susceptibility evidenced a deviation from the Pr3+ Curie-Weiss behavior in the same temperature range for which the resistivity anomaly occurs. This behavior is explained in terms of an induced magnetic moment at the CuO2, layers under strain. A Dzialoshinsky-Moriya interaction, associated to the orthorhombic distortions, is proposed to be the source of a weak canted ferromagnetic component, which develops in conjunction with an enhancement of the antiferromagnetic correlations. A comprehensive picture of the conduction mechanism for the whole system is presented in terms of a Kondo-like scattering of the mobile holes by the spin fluctuations at the conduction planes. T-c suppression was found to correlate with C, suggesting that the excitation which interacts with the carriers in the normal state is relevant for superconductivity. [S0163-1829(99)11505-4].5996557656

Magnon-assisted tunnelling in van der Waals heterostructures based on CrBr3

Van der Waals heterostructures, which are composed of layered two-dimensional materials, offer a platform to investigate a diverse range of physical phenomena and could be of use in a variety of applications. Heterostructures containing two-dimensional ferromagnets, such as chromium triiodide (CrI3), have recently been reported, which could allow two-dimensional spintronic devices to be developed. Here we study tunnelling through thin ferromagnetic chromium tribromide (CrBr3) barriers that are sandwiched between graphene electrodes. In devices with non-magnetic barriers, conservation of momentum can be relaxed by phonon-assisted tunnelling or by tunnelling through localized states. In contrast, in the devices with ferromagnetic barriers, the major tunnelling mechanisms are the emission of magnons at low temperatures and the scattering of electrons on localized magnetic excitations at temperatures above the Curie temperature. Magnetoresistance in the graphene electrodes further suggests induced spin–orbit coupling and proximity exchange via the ferromagnetic barrier. Tunnelling with magnon emission offers the possibility of spin injection

Effect of synthesis route on the structure of Nd_3-x}Ba_{3+x}Cu_6O_{14-2}_\delta (x=0, 1) system: a neutron diffraction study

Structural studies on Nd_{3-x}Ba_{3+x}Cu_6O_{14-2}_\delta with 0≤x≤1 were carried out by Rietveld refinement procedure using neutron diffraction data. The composition x=1 was prepared both by the solid-state method and the nitrate-decomposition method. Quantitative multiphase analysis coupled with variation in the method of synthesis has shown conclusively that Nd did substitute for Ba even in a stoichiometric composition $NdBa_2Cu_3O_{7 - \delta }$ , irrespective of the method of synthesis. The fractional atomic substitution of Nd at the Ba site has been determined to be about 15%. The composition x=0, synthesised by the nitrate-decomposition method, has been found to be tetragonal with the space group P4/mmm. Nd has been found to substitute for Ba according to $Nd(Ba_{0.75}Nd_{0.25})_2Cu_3O_{7 - \delta}$ and no random distribution of cations has been found along the c-direction. The observed tetragonality has been attributed to the additional oxygen taken into the basal (001) plane due to the substitution of trivalent Nd at the divalent Ba site

Neutron diffraction on Er1-xCaxBa2Cu3O7-delta (0.0 <= x <= 0.3) system: possible oxygen vacancies in Cu-O-2 planes

In the system Er1-xCaxBa2Cu3O7-delta with x = 0.0 to 0.3, the superconducting transition temperature (T-c), as measured from AC susceptibility, decreases with increasing Ca substitution, x. Detailed analysis of the powder neutron diffraction patterns of these samples shows a decrease in oxygen content with increasing x. The orthorhombic distortion decreases slightly and the c-parameter increases slightly with increasing x. Both, the buckling angle [(Cu(2)-O(2)-Cu(2) angle)] and the planer Cu(2)-O(2) distance in Cu-O-2 planes, increase with increasing x. Increased Cu(2)-O(2) bond distance indicates a slight decrease in p-type hole carriers in Cu-O-2 planes. On comparison with reported results on T-c vs. p-type carriers in high T-c superconducting compounds, it is inferred that decrease in p-type carriers alone cannot account for sharp T-c depression with increasing n in Er1-xCaxBa2Cu3O7-delta system. With increasing x, oxygen vacancies are created in Cu-O-2 planes, which along with increased buckling angle might be partly responsible for T-c suppression in this system. (C) 2000 Elsevier Science B.V. All rights reserved.338319720

Suppression of superconductivity with Pr substitution in Nd1-xPrxBaCaCu3O7 system

The structural, superconducting and magnetic properties of Nd1-xPrxBaCaCu3O7 system with x = 0.0, 0.10, 0.25, 0.35, 0.50, 0.75 and 1.0 have been investigated. X-ray diffraction results reveal that Pr substitutes isostructurally in NdBaCaCu3O7 (Nd:1113) superconductor with complete solubility. The superconducting transition temperature (T-c), measured by ac susceptibility technique, decreases with increasing x. However, suppression of T-c with increasing Pr substitution is less in Nd:1113 superconductor compared to that reported for Nd1-xPrxBa2Cu3O7 system. Interestingly, in the fully Pr substituted compounds of the above series, i.e., in PrBaCaCu3O7 and PrBaxCu3O7, the Pr moments order antiferromagnetically with T-N of 10 and 17 K, respectively. The present results along those reported earlier [V.P.S. Awana, J. Horvat, S.X. Dou, A. Sedky, A.V. Narlikar, J. Magn. Magn. Mater., 182 (1998) L280; V.P.S. Awana, S.X. Dou, S.K. Malik, Rajvir Singh, A.V. Narlikar, D.A. Landinez Tellez, J.M. Ferreira, J. Albino Aguiar, S. Uma, E. Gmelin, W.B. Yelon, J. Magn. Magn. Mater., 187 (1998) 192], clearly suggest that there is a correlation between the T-c suppression due to Pr and the magnetic ordering temperature of the fully substituted Pr moments in these systems. The T-N may be taken to be a measure of the strength of hybridization between the Pr-4f electrons with Cu-O conduction band, and hence a lower T-N may imply a less deleterious effect on superconductivity. (C) 1999 Elsevier Science B.V. All rights reserved.3164167111311