S. Sanna

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.

The freezing of spin and charge at low temperature in YBa2Cu3O6+x

Abstract We present the results of an extensive μSR reinvestigation of the doping dependence of the AF order in polycrystalline YBa 2 Cu 3 O 6+ x samples (0 x x >0.2, we detected a spin freezing correlated to the charge freezing of the holes in the CuO 2 planes. The data may be fitted to a model of size-dependent reduction of the staggered magnetization implied in a stripe scenario. The hole concentration dependence of these freezing phenomena is mapped onto the phase diagram of YBa 2 Cu 3 O 6+ x .

Investigation of a Peaked Feature in the Magnetic Susceptibility of YBa2Cu3O6.30 Samples

The static magnetic susceptibility of two different YBa2Cu3O6.30 samples has been measured at different fields in the range 2 - 300 K, using a superconducting quantum interference device magnetometer; one sample has been prepared by oxygen intercalation, the other one by deintercalation. The susceptibility shows a peak near 45 K in both samples, which depends on the field and the magnetic history. The susceptibility of semiconducting and superconducting compounds, with an oxygen content O6.20 and O6.41, respectively, has also been investigated. The presence of the peak in the YBa2Cu3O6.30 samples has been explained by the combined effect of regions with a Curie-like behaviour and superconducting regions. The origin of these regions is discussed.

Magnetic Susceptibility of the Cluster Compounds Mo6Se8 and Mo6Te8

The magnetic susceptibility of the cluster compounds Mo6Se8 and Mo6Te8 has been measured at temperatures between 82 and 330 K, using a Faraday balance. The paramagnetic and diamagnetic components of the susceptibility have been analyzed. The Pauli component was evaluated using the density of states at the Fermi level obtained by band structure calculations,while the core component was evaluated using the calculated atomic core diamagnetism. The paramagnetic susceptibility of Mo6Se8 is due mainly to the Pauli contribution, while the Van Vleck contribution is small, in agreement with the metallic feature of the compound. The paramagnetic susceptibility of Mo6Te8 is due mainly to the Van Vleck term,while the Pauli contribution of the conduction electrons is very small. The result points out that the Mo6 clusters in the telluride retain their molecular character, with small intercluster interactions.