J. R. Kempton

Temperature dependence of the magnetic penetration depth in YBa2Cu3O7 measured by muon spin rotation

We report an improved measurement of the temperature dependence of the magnetic penetration depth in sintered YBa2Cu3O77 using muon spin rotation. The effective isotropic average of the magnetic penetration depth (λ) is estimated from the second moment of the field distribution in the vortex state in an external field of 15kG. The low temperature behaviour of λ is still consistent with an s-wave pairing mechanism although there are deviations from the conventional BCS-like behaviour for T/Tc > 0.2.

Magnetic ordering in YBa2Cu3Ox studied by μ+ spin rotation☆

YBa2Cu3Ox is known to be antiferromagnetic (AFM) for x ≲ 6.45 but the details of its sublattice magnetization(s) are still controversial. A zero-field μ+SR investigation of the x- and T-dependence of the local fields at several muon sites reveals sharp changes at 10K and 80K for an oriented powder sample with x ≈ 6.0, but other x ≈ 6.0 samples do not show the same features. The direction of the local field at one μ+ site is shown to be along the ĉ-axis. For x < 6.0 the samples still show local spin freezing up to 300K, but coherent AFM order is lost even at 3K.

Coexistence of superconductivity and magnetic order in YBa2Cu3Ox

Abstract Resistivity, susceptibility and μ + SR measurements have been used to investigate the ( x , T ) phase diagram of YBa 2 Cu 3 O x . Carefully annealed samples are antiferromagnetic (AFM) insulators for 6.0 ≲ x ≲ 6.35 and nonmagnetic superconductors (SC) for 6.5 ≲ x ≲ 7.0; SC coexists with AFM or spin glass (SG) static magnetic order at low temperatures for 6.38 ≲ x ≲ 6.48. A sample with x = 6.462 is SC below 25 K and simultaneously magnetic below 10 K; the internal diamagnetism of the SC state is progressively reduced as local spin freezing sets in at low temperatures.

Antiferromagnetism and superconductivity in YBa2Cu3Ox studied by μSR

We have used the technique of muon spin relaxation to study the competition between antiferromagnetism (AFM) and superconductivity (SC) in oxygen deficient YBa 2 Cu 3 O x for 6.0 x = 6.0 down to 2.5K for x = 6.40. Samples with x near 6.4 were both SC and AFM. In the x = 6.1 sample, where there is a narrow distribution of TNs, we have observed the critical slowing down of the Cu spins at the average TN.

μSR study of magnetism in La1.85Sr0.15CuO4 and YBa2Cu3Ox below 90 mK

Abstract The internal magnetic fields in La 1.85 Sr 0.15 CuO 4 and YBa 2 Cu 3 O x have been investigated below 90 mK using muon spin rotation. In YBa 2 Cu 3 O x the magnetic order parameter remains constant with increasing x up until x =6.30 and then rapidly approaches zero just above x =6.44. We find little evidence for static or slowly fluctuating electronic moments in superconducting La 1.85 Sr 0.15 CuO 4 .