Antiferromagnetism and superconductivity in oxygen-deficientYBa2Cu3

Abstract

Positive-muon spin-rotation and -relaxation measurements of the oxygen-deficient perovskite YBa2-Cu30 x have revealed local antiferromagnetic order for 6.0^x^6.4 with a Neel temperature TN that decreases rapidly with increasing oxygen content x. For slowly annealed samples with 6.35^x^6.5 the superconducting transition temperature T c increases smoothly with x from 25 K at x =6.348 to 60 K at x =6.507. Two such samples with x =6.348 and x =6.400 appear to "switch" from superconductivity to antiferromagnetic order at lower temperatures.PACS number: 76.75.+i, 74.70.Vy, 75.50.EeThe recent discovery 1 of superconductivity at the anomalously high temperature of T c «90 K in the perovskite YBa2Cu30 x (6.9^x^7.0) has stimulated theorists to explore new mechanisms for superconductivity. Several such theories 2 involve frustrated antiferromagnetic couplings between copper and/or oxygen ions in the CuC>2 planes that these materials have in common with the slightly lower-T c perovskite Lai.ssSro.isCuC^-s. It was therefore interesting to learn, both from neutron diffraction 3 and from positive-muon spin-rotation and -relaxation (/x + SR) and susceptibility measurements, 4 that the (insulating) parent compound La2Cu04-s exhibits antiferromagnetic (AFM) order below a Neel temperature TN that depends critically upon the oxygen deficiency 8 (TN increases with increasing <5), lanthanum stoichiometry, and/or doping of Sr for La. For instance, we have found that replacing La2 by La1.98Sro.02 reduces TN from around 250 K to less than 15 K. Similar AFM ordering was discovered in the oxygen-deficient YBa2Cu3-Ojc materials (insulating for x;$6.3) with use of muon spin rotation. 5 Although it has been more difficult to detect the antiferromagnetism in this material by other techniques, recent neutron-diffraction measurements on an oriented powder have now confirmed the presence of long-range AFM order. 6In this Letter we report on the competition between AFM and superconductivity (SO in YBa2Cu30 x as a function of x, using the technique of p. + SR. 7 ' 8 The positive muon serves as a microscopic probe of the local magnetic environment at interstitial sites and is sensitive to and can differentiate between AFM and SC in the bulk of the sample.The samples used in these measurements were sintered powders of YBa2Cu30 x prepared by two rather different methods. In the "quench" method, samples were heated in controlled atmospheres of oxygen and/or argon and allowed to equilibrate to the oxygen content determined by thermogravimetric analysis on test samples, using as a reference neutron-diffraction results from Jorgensen et al. 9 which show that as the oxygen content x is decreased, oxygen atoms are selectively removed first from the CuO "chains," leaving the CuC>2 "planes" essentially intact down to x =6.0 where the "chains" are fully deoxygenated. The samples were then dropped directly into liquid nitrogen and transported under argon to TRIUMF for p + SR experiments. In the "slow-anneal" method, a "mother batch" of YBa2Cu30jc powder was p...

Muon spin rotation investigation of the pressure effect on the magnetic penetration depth in YBa2Cu3Ox

“…For type-II superconductors in the vortex state in an applied field of B app ≪ B c2 (B c2 is the upper critical field) the square root of the second moment of the muon depolarization rate σ is inversely proportional to the square of the magnetic penetration depth: σ ∝ 1/λ 2 (Refs. 4,46,47) and therefore directly related to the superfluid density: ρ s ∝ 1/λ 2 ∝ σ. For a polycrystalline sample of a highly anisotropic and uniaxial superconductor the dominant contribution to the muon depolarization originates from the in-plane magnetic penetration depth λ ab = λ eff /1.31, where λ eff is an effective (averaged) magnetic penetration depth.…”

“…Detailed muon spin rotation (µSR) studies of the magnetic penetration depth λ and the superfluid density ρ s ∝ 1/λ 2 were performed on poly-and single crystals of YBa 2 Cu 3 O x at ambient pressure. [3][4][5][6][7][8][9][10] However, the key question concerning the pairing mechanism responsible for high temperature superconductivity is still not resolved, and is subject of intense debates. Although it is widely believed that magnetic fluctuations play a dominant role in the pairing mechanism, 11 oxygen isotope effect (OIE) studies indicate that lattice degrees of freedom are essential for the occurence of superdonductivity.…”

Muon spin relaxation studies of incommensurate magnetism and superconductivity in stage-4La2CuO4.11andSavici1, Fudamoto2, Gat3 et al. 2002Phys. Rev. BSelf Cite

“…Subsequently, SR studies on La 2 CuO 4 , 28 (La,Li) 2 CuO 4 , 29 La 2Ϫx Sr x CuO 4 , [30][31][32][33][34] and YBa 2 Cu 3 O y , 34,35 were performed to characterize magnetic phase diagrams as a function of hole concentration and also to study details of the spin glass states near xϭ0.05.…”

Nucleation of superconductivity in ceramic oxides

“…It has been shown that in the mixed ternary system (Sml-,Er,) Rh4B4 LT,SC and A F coexist for small Er concentrations, and t,he manner in which AB changes to ferromagnetism was considered [5]. In ra.re earth HT,SC it has been shown that in the mixed ternary system (La,-,Sr,) CuO,, the NQel temperature T, is still non-vanishing for replacements of La, by La,.o,Sro,2 [2]. Neutron-diffraction measurements on an oriented powder of YBa,Cu,Od have confirmed the presence of AF in this material [6].…”