H. Maletta

Study of La2CuO4 and related compounds by μSR

The spontaneous muon precession frequency and relaxation rate were measured in several La-based Cu-oxide samples of La2CuO4 with different stoichiometry in order to study the influence of La-vacancy, Sr-doping and O-doping on magnetism and super-conductivity. From the measured frequency at low temperatures in the magnetically ordered samples and the relaxation rate in the normal state of superconducting samples the muon site was determined. We find the muon to be on the face of the unit cell of La2CuO4. 1 Å away from the apical oxygens ions O(2), favoring the typical bond length of 1 Å for O−H.

Identification ofμ +-sites in the 1-2-3 compoundin the 1-2-3 compound

Possibleμ+ sites have been identified by a comparison of measured spontaneous internal fields in YBa2Cu3O6+δ and REBa2Cu3O7−δ and of measured second moments and width of transverse field powder spectra with the corresponding calculated quantities. In the YBa2Cu3O7 system only one possibleμ+ site emerges at a distance of ∼1.05 A from a chain oxygen O(4) at the position (0.15(1), 0.44(1), 0.071(1)). In the system YBa2Cu3O6 the only possibleμ+ sites are near to an oxygen O(1) with z/c=0.133 and the same distance as above. The analysis leads also to improved valuesμHo = 2.2(1)μB andμCu = 0.67(4)μB and to a determination of the latters direction:μCu ‖〈110〉.

Measurements of the London penetration depth in Bi-based high-T c compounds

The muon spin relaxation was measured in the high-Tc superconductors Bi2Sr1.3Ca0.7 CuO6.15, Bi2Sr2CaCu2O8 and Bi2PbxSr2Ca2Cu3O10. We present our method to determine the London penetration depth perpendicular toc-axis λ⊥ (0) taking also contributions from the anisotropic magnetization and nuclear dipoles to the muon frequency spectrum into account.

Zero-field μSR study of ErBa2Cu3Ox for various oxygen contentx

Results from zero-field μSR experiments are presented, performed on the high-Tc compounds ErBa2Cu3Ox for various oxygen contentx with 6≤x≤7 at temperatures between 40 mK and 300 K. The aim was to study the magnetic ordering behavior of the Cu moments and the Er moments, and its interplay with superconductivity.

Transverse fieldμ+ SR investigations of rare earth substituted 1-2-3 compoundsSR investigations of rare earth substituted 1-2-3 compounds

Transverse field studies (0.3 T) in HoBa2Cu3O7, DyBa2Cu3O7 and ErBa2Cu3O7 (x=6.40. 6.45, 6.53, 7) were undertaken with the aim of detecting a possible 4f-moment inducedμ+ Knight shift which could elucidate the nature of the magnetic coupling among the 4f-moments and a possible interference with superconductivity. AboveTc no shift could be detected in any of the systems except in HoBa2Cu3O7 where a split signal appears involving a positive and a negative shift. Unexpected shifts may be present belowTc.

Magnetism and superconductivity in the ErBa2Cu3OA system

Transverse field μSR studies of the system ErBa2Cu3Ox with x=6.4, 6.53 and 7 reveal a split signal with each component displaying a distinct paramagnetic or Knight shift related to the Er 4f-moments. This implies the presence of transferred hyperfine fields even in the superconducting state.