Showing papers by "J. Albino Aguiar published in 1997"
TL;DR: In this paper, the role of Zn in the superconducting transition of the LaBaCaCu{sub 3}O{sub 7{minus delta}} (LBCCO) system has been investigated and the authors found that the conduction mechanism of electrons appears to follow a crossover from the purely metallic regime to the localization regime due to either weak localization or electron-electron interaction effects after about 15% Zn.
Abstract: Resistivity and ac susceptibility of Zn-doped samples of the LaBaCaCu{sub 3}O{sub 7{minus}{delta}} (LBCCO) system have been measured for Zn content of 05{percent}, 10{percent}, 15{percent}, 20{percent}, 25{percent}, and 30{percent} atwt X-ray diffraction has been used to find the lattice parameters of the samples The samples remain tetragonal for all the considered concentrations of Zn Idometry and thermogravimetric analyses have been done to estimate the oxygen content of different samples Analyzing the resistivity and ac susceptibility data, the following conclusions are drawn about the role of Zn in the LBCCO samples (1) The conduction mechanism of electrons appears to follow a crossover from the purely metallic regime to the localization regime due to either weak localization or electron-electron interaction effects after about 15{percent} Zn (2) The superconducting transition as revealed by the resistivity vs temperature curves or susceptibility vs temperature curves becomes sharper with Zn increasing content of Zn up to 10{percent} After 15{percent} the resistive and ac susceptibility transitions become broader with increasing Zn (3) T{sub c} depression up to Zn content of 10{percent} seems due to direct suppression of the effective pairing interaction, while at and above 25{percent} Zn T{sub c} depression is expected to be due to disorder effectsmore » such as reduction of density of states at the Fermi energy {copyright} {ital 1997} {ital The American Physical Society}« less
30 citations
TL;DR: In this article, the results of superconductivity, normal state magnetic susceptibility and heat capacity measurements on the tetragonal CaLa1-xPrxBaCu3O7 compound were presented.
Abstract: We present the results of superconductivity, normal state magnetic susceptibility and heat capacity measurements on the tetragonal CaLa1-xPrxBaCu3O7 compound. Ac susceptibility measurements show that the transition temperature Tc of the unsubstituted sample decreases with an increase in the Pr concentration. Normal state dc magnetic susceptibility measurements performed in an applied field of 0.5 T show a Curie–Weiss behaviour in terms of the paramagnetic moment of Pr. The effective paramagnetic moment of Pr appears to be intermediate between those of the free Pr3+ and Pr4+ ions. For the nonsuperconducting samples i.e., x = 0.70 and 1.0, we observe an antiferromagnetic ordering temperature TN of nearly 4 K and 8 K respectively. The X-ray diffraction results show that the CaPrBaCu3O7 compound is free from other phases, having a minor (less than 8%, in terms of peak intensity) impurity phase. The lower TN (8 K) of PrBaCaCu3O7 as compared to the known antiferromagnetic ordering temperature of 17 K for PrBa2Cu3O7 indicates a less deleterious effect of Pr in the present case.
4 citations
TL;DR: In this article, the results of structure, superconductivity and normal state of the CaLaBaCu 3−n Fe x O 7 superconductor, obtained using powder X-ray diffraction and a SQUID (superconducting quantum interface device) magnetometer have been presented.
Abstract: The results of structure, superconductivity and normal state, i.e. above T c , magnetism of the CaLaBaCu 3− n Fe x O 7 superconductor, obtained using powder X-ray diffraction and a SQUID (superconducting quantum interface device) magnetometer have been presented. The critical temperature ( T c ) of the pristine sample determined from ac susceptibility measurements decreases with Fe concentration. The normal state high field (5 kOe) dc magnetism of these samples infers a nearly temperature independent and relatively small molar susceptibility for the x = 0.0 sample, while for the Fe doped samples the same follows a Curie-Weiss temperature dependence, in terms of a localized moment presumably on doped Fe ions. The effective paramagnetic moment on Fe in the doped samples appears to be less than known Fe 2+ /Fe 3+ moments. Namely it is 5.09, 4.53 2.79 and 3.37 μ B respectively for x = 0.03, 0.06, 0.12 and 0.24 samples. The reduced moment of Fe is probably due to the presence of crystal field effects in these systems, which has an increasing trend with an increase in Fe concentration.
3 citations
TL;DR: In this paper, the results of superconductivity, normal state magnetism, heat capacity and neutron diffraction of the La-site Pr substituted CaLa 1−x Pr x BaCu 3 O 7 system were presented.
Abstract: We present the results of superconductivity, normal state magnetism, heat capacity and neutron diffraction of the La-site Pr substituted CaLa 1−x Pr x BaCu 3 O 7 system The T c vs x behaviour of this system appears to be different than that predicted for orthorhombic La 1−x Pr x BaCaCu 3 O 7 system Normal state dc magnetic measurements done in an applied field of 5kOe show a Curie-Weiss behaviour in terms of the paramagnetic moment of Pr The effective paramagnetic moment of Pr appears to be the intermediate between that of the free Pr 3+ /Pr 4+ known moments For the non superconducting samples, ie, for x=070 and 10, we observed an antiferromagnetic ordering temperature T N of nearly 4K for the former and 8K for the later from our dc magnetic and heat capacity measurements The X-ray and neutron diffraction result show that Pr substitutes isostructurally until x=10 in CaLa 1−x Pr x BaCu 3 O 7 system with a few small intensity lines of unreacted BaCuO 2 and CaCuO 2 The lower T N of 8K for PrBaCaCu 3 O 7 than the known 17K for PrBa 2 Cu 3 O 7 is presumably due to the intermixing of Pr and Ba site in the former compound
2 citations
TL;DR: The results of superconductivity, structure and normal state magnetism of the CaLaBaCu3−x(Zn,Fe)xO7 are studies by x-ray diffraction and SQUID magnetization measurements as discussed by the authors.
Abstract: The results of superconductivity, structure and normal state magnetism of the CaLaBaCu3−x(Zn,Fe)xO7 are studies by x-ray diffraction and SQUID magnetization measurements X-ray diffraction results show that both Zn-and Fe substitute isostructurally in CaLabaCu3O7 system The superconducting transition temperature Tc of the samples, determined from ac susceptibility measurements decreases with increasing Zn or Fe concentration The relative Tc depression rate (dTc/dx), is larger (12K/at%) for Zn than the Fe (6Kk/at%) substituted samples For both the Zn and Fe substituted samples a Curie-Weiss behaviour is observed due to the presumed creation of local moments on Cu for Zn doped samples, and to the magnetic moment of Fe3+/Fe4+ ions in case of Fe substituted samples
2 citations