J.M. Ferreira
Federal University of Pernambuco
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Featured researches published by J.M. Ferreira.
Modern Physics Letters B | 1996
V. P. S. Awana; D.A. Landinez; J.M. Ferreira; J. Albino Aguiar; Rajvir Singh; A.V. Narlikar
Both on-site Zn substitution and oxygen deficiencies in the CaLaBaCu3O7 system decrease the superconducting transition temperature Tc of the pristine sample. We observed that the normal state magnetism, measured in a field of 5 KOe, shows a Curie-Weiss behavior, in terms of a localized magnetic moment, presumably on Cu sites, in both cases. The pristine system, i.e. without Zn substitution or oxygen deficiencies, shows a weakly temperature dependent small magnetic susceptibility, in the normal state, i.e. above Tc. It has been argued that the normal state magnetism of HTSC systems plays a vital role in determining the Tc of these materials.
Physica C-superconductivity and Its Applications | 2000
J. Albino Aguiar; Cléssio Leão S. Lima; Yogendra Prasad Yadava; D.A. Landínez Téllez; J.M. Ferreira; Erivaldo Montarroyos
In this work we have studied the effect of CuS doping on Bi-2212 (nominal composition Bi 2+y Sr 3-y- n Ca n [(CuO) 1-x (CuS) x ] 2 O 6+δ , (0 < x < 0.1, 0 < y < 0.1 and 0.8 < n < 1) superconductors. An improvement in T c of the CuS doped Bi-2212 superconductors is observed in these studies. Most likely improvement in T c of the CuS doped Bi-2212 superconductors is caused by the modifications in the oxygen stoichiometry of the samples due to incorporation of S in the Bi-2212 lattice, with a consequent improvement in hole concentration.
Physica C-superconductivity and Its Applications | 1998
J. Albino Aguiar; C. C. de Souza Silva; Yogendra Prasad Yadava; D.A. Landinez Tellez; J.M. Ferreira; J. Guzman; E. Chavira
Abstract A complex perovskite oxide HoBa 2 SbO 6 in the Ho–Ba–Hf–O, rare-earth based oxide system, has been synthesised and sintered as a single phase material. The structure, microstructure, quantitative elemental analysis and magnetic properties of this material have been studied by X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) techniques and magnetic susceptibility measurements. Significant presence of superstructure reflection lines in the XRD spectra of HoBa 2 SbO 6 reveals that it is an ordered complex perovskite oxide. Magnetic susceptibility measurements show that HoBa 2 SbO 6 presents a paramagnetic behaviour at low temperature (5–300 K). Microstructure and EDX analysis show that sintered HoBa 2 SbO 6 has homogeneous surface morphology with uniform particle size (1–2 μm) distribution and there is no evidence of impurity in the single phase sintered HoBa 2 SbO 6 . The chemical stability of HoBa 2 SbO 6 with YBa 2 Cu 3 O 7− δ superconductor was studied. This study shows that HoBa 2 SbO 6 is chemically compatible with YBa 2 Cu 3 O 7− δ and it did not have deleterious effect on the superconducting transition temperature of YBa 2 Cu 3 O 7− δ . Also, HoBa 2 SbO 6 melts congruently and single crystals could be grown from the melt. In view of these favourable characteristics, HoBa 2 SbO 6 could be used as a potential substrate material for YBa 2 Cu 3 O 7− δ superconductor film.
Journal of Magnetism and Magnetic Materials | 2001
A. Rosales-Rivera; J.M. Ferreira; F.C. Montenegro
Abstract The random-field Ising model (RFIM) system Fe 0.42 Zn 0.58 F 2 is studied by magnetization and AC susceptibility measurements, under finite DC applied fields ( H ). For weak random fields (corresponding to H T c ( H ) is accompanied by the critical slowing down inherent to the random field problem. For higher H , the PT is destroyed and a glassy dynamics dominates the magnetic behavior.
Superconductor Science and Technology | 1999
D.A. Landinez Tellez; Yogendra Prasad Yadava; J.M. Ferreira; J. Albino Aguiar
Chemical and physical compatibility of MgO with (LBCCO) high- superconductors have been studied by x-ray diffractometry and magnetic measurements on composites containing 0-100 vol% of MgO component. X-ray diffractometry studies carried out on composite show that MgO is chemically non-reactive with LBCCO superconductors even up to 80 vol% addition of MgO and severe heat treatment at for 30 h. Lattice matching between MgO and unit cells is fairly well (lattice mismatch ). Magnetization measurements carried out on composite show that no deleterious effect on the superconducting properties of is caused by MgO addition. Thus we infer that MgO is chemically and physically compatible with superconductors and MgO substrates could be used for the fabrication of high- LBCCO superconducting films.
Journal of Magnetism and Magnetic Materials | 1998
D.A. Landinez Tellez; J.M. Ferreira; J. Albino Aguiar
Abstract The results of superconductivity and normal-state magnetism of the CaLaBaCu3 − xCoxO7 superconductor for x = 0.0–0.24 are studied by X-ray diffraction and SQUID magnetization. The transition temperature Tc of the samples, determined from AC susceptibility measurements decreases with an increase in the dopant Co concentration. The normal-state high-field (5 kOe) DC magnetism inferred that the pure sample (x = 0.0) has a small and nearly temperature-independent molar susceptibility, while the Co-doped samples follows the Curie-Weiss relation in terms of the paramagnetic moment on the dopant Co.
Modern Physics Letters B | 1997
V. P. S. Awana; Rajvir Singh; D.A. Landínez Téllez; J.M. Ferreira; J. Albino Aguiar; S. Uma; E. Gmelin; A.V. Narlikar
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.
Physica C-superconductivity and Its Applications | 2001
Yogendra Prasad Yadava; Erivaldo Montarroyos; J.M. Ferreira; J. Albino Aguiar
Abstract A new complex cubic perovskite oxide Sr 2 HoHfO 5.5 has been prepared by solid state reaction process. X-ray diffraction studies show that Sr 2 HoHfO 5.5 has a A 2 BB ′ O 6 type complex cubic perovskite structure and presence of the significant intensities of superstructure reflections in the X-ray spectrum reveal that it is an ordered complex cubic perovskite oxide. The experimental value of the lattice parameter of Sr 2 HoHfO 5.5 , is a =8.1725 A. Based on the doubling of primitive ABO 3 cubic perovskite unit cell, (1/2) a =4.0862 A of Sr 2 HoHfO 5.5 is comparable to the lattice parameter a =3.8227 A of YBCO superconductor. Sr 2 HoHfO 5.5 has good lattice matching (lattice mismatch ∼6%) with YBCO superconductor. The dc magnetic susceptibility of Sr 2 HoHfO 5.5 , measured in the temperature range 5–300 K shows a Curie–Weiss behavior. Using a Curie–Weiss law fitting we obtain a effective magnetic moment per Ho 3+ ion in Sr 2 HoHfO 5.5 of 9.76 μ B . This value is slightly lower than the spin-only moment (10.60 μ B ) expected for an isolated Ho 3+ ion.
Physica C-superconductivity and Its Applications | 1997
V. P. S. Awana; Rajvir Singh; D.A. Landínez Téllez; J.M. Ferreira; J. Albino Aguiar; A.V. Narlikar
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.
Journal of Magnetism and Magnetic Materials | 1992
J. Albino Aguiar; J.M. Ferreira; M. T. de Melo; C. Schettini; F. Schneider; M.V.S. Barbosa; L.R.Madeiro de Melo; A.C. Pavão; J. M. van Ruitenbeek
Abstract In this paper we present X-ray diffraction, resistivity and ac magnetic susceptibility studies of NiS-substituted YBa 2 Cu 3 O 7−δ superconductors. A set of samples with nominal composition YBa 2 [(CuO) 1− x (NiS) x ] 3 O 4−δ were prepared. They show a small increase in T c and a decrease of the room-temperature (RT) resistivity ϱ 300 for small substitution of CuO by NiS. However as the NiS concentration is increased T c decreases and ϱ 300 was higher than that of the undoped sample. The results seem to agree with Paulings resonating valence bond theory for the high- T c copper oxides superconductors [1]. This theory predicts an increased T c due to the great number of the unsynchronized resonances generated as the insulating CuO is substituted by NiS.