Local magnetism in superconducting YBa2Cu3O6+x

Oxygen-deficient YBa₂Cu₃O_6+x samples were investigated by the muon spin rotation technique in zero external field. In an intermediate oxygen concentration region we find strongly relaxing μSR signals indicating the existence of internal magnetic fields. The strongly relaxing signals were observed only in samples with superconducting transition temperatures below 50 K. As an interpretation of the data we suggest that magnetic ordering and superconductivity coexist in these samples within regions of extensions of a few lattice constants, but not necessarily on the same sites.     

Investigation of superconductivity and magnetism in ceramic YBa2Cu3O6+x

In this work the magnetic and superconducting properties of YBa₂Cu₃O_6+x , ceramic samples are studied with regard to there preparations technology and oxygen content. It is shown that at 0.41≤x≤0.45 the magnetic and superconducting states coexist.     

Magnetic phase present in YBa2(Cu1−x Fe x )3O6+δ oxides

The Mössbauer study of⁵⁷Fe: YBa₂Cu₃O_6+δ oxides was very important to establish the preferential occupation of Cu(1) site by Fe at very low concentrations. Recent determination of antiferromagnetic ordering for Cu moments in Cu(2) sites (T≈450 K) and our early observation of a small proportion of a magnetic phase at room temperature for Fe:YBa₂Cu₃O₆ lead us to perform systematic studies of YBa₂(Cu_1?x Fe _x )₃O₆ withx=0.005, 0.03, 0.05, 0.10 and 0.15 in order to obtain information about the iron occupation of Cu(2) sites.     

Electrooptical effect in YBa2Cu3O6+x films

Optical absorption in YBa₂Cu₃O_6+x metal films carrying a direct current up to 100 mA is investigated. For films with a highly nonlinear I-V curve the current is observed to have a strong influence on interband absorption. The effect is not observed in the region of optical transitions at local levels. The results are analyzed from the standpoint of carrier localization and delocalization processes. Fiz. Tverd. Tela (St. Petersburg) 39, 1747–1749 (October 1997)     

Theoretical study ofμ + site in YBa2Cu3O x site in YBa2Cu3O x

The muon is a useful probe of magnetic fields in superconductors, but knowing the field seen by the muon is often of limited value until we know where the muon is in the crystal lattice. Here we employ two independent theoretical methods to search for candidate muon sites:the potential energy field method, which seeks the minimum of the electrostatic potential of theμ ⁺, and themagnetic dipolar field method, which compares the calculated magnetic field (due to host electronic or nuclear dipolar fields) with the observed local fields at the muon. Work supported by Canadian NRC and NSERC.     

Nanoscopic coexistence of magnetism and superconductivity in YBa2Cu3O6+x detected by muon spin rotation

We performed zero and transverse field muon spin rotation experiments on a large number of YBa2Cu3O6+x samples. We detect the coexistence of antiferromagnetic (AF) short range magnetism with superconductivity below T(f) < or = 10 K in compositions 0.37 < or = x < or = 0.39. Most muons experience local AF fields, even when a SQUID detects a full superconducting volume fraction, which points to a local minimal interference organization of short AF stripes embedded in the superconductor. A detailed phase diagram is produced and the consequences of the minimal interference are discussed.     

Effect of loading on the chemical potential of oxygen atoms in YBa2Cu3O6+x (YBCO) and PrBa2Cu3O6+x (PBCO)

The effect of loading on the chemical potential of oxygen atoms has been studied in the YBCO and PBCO isostructural compounds, with the former exhibiting HTSC, and the latter, not. Application of a load to both YBCO and PBCO in the orthorhombic phase causes an increase in the chemical potential within the 0.5<x<0.8 interval, which is interpreted as a phase-separation region. This effect is associated with an increase in the fraction of an ordered phase possessing a smaller specific volume. It is also related to the additional compressibility of the material. In the tetragonal phase this effect is observed only in YBCO. The absence of the effect in PBCO implies the electron-phonon coupling in this material has a different nature. Fiz. Tverd. Tela (St. Petersburg) 41, 572–576 (April 1999)     

Magnetic properties of undoped YBa 2 Cu 3 O 6 + x system

In the present paper, we study the magnetic properties of bilayer cuprate antiferromagnets. In order to evaluate the expressions for spin-wave dispersion, sublattice magnetization, Néel temperature and the magnetic contribution to the specific heat, the double time Green's function technique has been employed in the random phase approximation (RPA). The spin wave dispersion curve for a bilayer antiferromagnetic system is found to consist of one acoustic and one optic branch. The “optical magnon gap” has been attributed solely to the intra-bilayer exchange coupling (J _⊥ ) as its magnitude does not change significantly with the inter-bilayer exchange coupling (J_z). However J_z is essential to obtain the acoustic mode contribution to the magnetization. The numerical calculations show that the Néel temperature (T _N ) of the bilayer antiferromagnetic system increases with the J_z and a small change in J_z gives rise to a large change in the Néel temperature of the system. The magnetic specific heat of the system follows a T² behaviour but in the presence of J_z it varies faster than T². Received 13 July 2000 and Received in final form 14 May 2001     

NMR and spin-lattice relaxation rate of89Y,63Cu in radiation disordered YBa2Cu3O6.9

NMR line shifts and spin-lattice relaxation rates of⁸⁹Y and⁶³Cu in YBa₂Cu₃O_6.9 were measured in disordered samples irradiated by fast neutrons with a fluence of: ?=5·10¹⁸ cm^?2 (T _c ^ons =70 K), ?=1.2·10¹⁹ cm^?2 (T _c ^ons =20 K), in order to investigate the evolution of spin susceptibility χ_S under irradiation. According to the data obtained, χ_S decreases markedly as structural disorder accumulates in the samples. The variation of χ_S is related closely to that observed in oxygen-depleted YBa₂Cu₃O_7?δ compounds with nearly the sameT _c value. The data for yttrium display some features that are absent in oxygen-depleted samples. The different temperature dependence of the⁸⁹Y and⁶³Cu Knight shifts and the increase of the⁸⁹Y spin-lattice relaxation rate in irradiated samples are discussed in terms of the electron localization effects arising in the CuO₂ planes due to the radiation-induced structural disorder.