R. S. Kwok

Muon-spin-relaxation study of magnetism in ErBa2Cu3O6.2

The copper magnetism of ErBa2Cu3O6.2 is examined by transverse‐field (TF) and zero‐field (ZF) muon‐spin relaxation (μSR). These data indicate two magnetic phases with TN1≂330 K and TN2∼65 K. The second phase is signaled by deviation of the ZF‐μSR frequencies from a standard magnetization curve and an abrupt change in the TF‐μSR relaxation rate. A relaxation feature indicates a muon depolarization mechanism with a T3/2 dependence in the low‐temperature phase. Observed fields are compared to those calculated for proposed magnetic structures.

μSR investigation of magnetism and superconductivity in (Y1−xPrx)Ba2Cu3O7

Abstract Muon spin rotation and relaxation techniques have been used to study the superconductivity and magnetism in (Y 1− x P x )Ba 2 Cu 3 O 7 (0⩽ x ⩽1) and PrBa 2 Cu 3 O 6 . Clear evidence for magnetic ordering of the Cu moments within the Cu-O planes is seen. Additionally, a lower magnetic transition is observed which, based upon previous work, has been associated with the ordering of Pr moments on the Y sublattice of the YBa 2 Cu 3 O 7 structure. For x = 1, the upper Neel temperature T N1 is ∼270 K and the magnitude of the fully developed local magnetic field is ∼16 mT. Below the lower Neel temperature T N2 = 17 K, the magnitude of the static field is reduced to ∼ 12mT. For 0.4⩽ x ⩽0.54, there appears to be a coexistence region of long range magnetism and superconductivity.

Transverse-and zero-field μSR investigation of magnetism and superconductivity in (Y1−xPr x )Ba2Cu3O7

Zero-field muon-spin-rotation (μSR) measurements on (Y1−xPrx)Ba2Cu3O7 [x=1.0, 0.8, 0.6, and 0.54] show evidence for antiferromagnetic ordering of the Cu moments within the Cu−O planes, with Néel temperatures 285, 220, 35. 30 and 20 K, respectively. Forx=1.0 the local muon magnetic field is ≈16 mT, but decreases to ≈12 mT at 17K, due to additional magnetic ordering. The zero-field data, in conjunction with transport data, allow construction of a complete phase diagram for this system. Transverse-field (1 kOe) μSR data forx=0.2 (Tc=75 K) show that the muon depolarization is determined primarily by the Cu nuclear moments forT>Tc, and by the vortex state forT<Tc. Fitting the superconducting-state data to a BCS model yields an extrapolated zero-temperature magnetic penetration depth of 2170 Å.

Anisotropy inc-axis oriented YBa2Cu3O7−δ

Muon spin relaxation (μSR) data taken at LAMPF on ac-axis oriented fine powder sample of YBa2Cu3O7−δ (YBCO) embedded in epoxy are analyzed for relaxation rate anisotropy. Clear differences beyond simple magnetic field penetration depth anisotropy are observed forB‖c andBc. The low-temperature anisotropy ratio is consistent with oriented ceramic data. Small crystallite size and anisotropic flux pinning characteristics are suggested as the fundamental cause of the additional effects.