Temperature and doping dependence of the penetration depth in Bi2Sr2CaCu2O8+ delta

Magnetic anisotropy of a cyclic octanuclear Fe(III) cluster and magneto-structural correlations in molecular ferric wheels

The magnetic anisotropy of the cyclic octanuclear Fe(III) cluster [Cs subsetFe(8)[N(CH(2)CH(2)O)(3)](8)]Cl was investigated. Based on a spin Hamiltonian formalism and the consequent use of all symmetries, the magnetic anisotropy could be calculated exactly to first order, i.e., in the strong exchange limit. Experimentally, the magnetic anisotropy was investigated by magnetic susceptibility and high-field torque magnetometry of single crystals. The field and angle dependence of the torque at 1.7 K could be accurately reproduced by the calculations with one single parameter set, providing accurate results for the coupling constant and single-ion zero-field-splitting. These magnetic parameters are compared to those of several related hexanuclear ferric wheels and are discussed with respect to magneto-structural correlations for both coupling constant and single-ion anisotropy.

Pressure dependence of the irreversibility line in Bi2Sr2CaCu2O(8+delta): role of anisotropy in flux-line formation

One of the important problems of high-temperature superconductivity is to understand and ultimately to control fluxoid motion. Here we present data on the pressure dependence of the irreversibility line measured up to 2.5 GPa. We observe that the application of pressure changes the interplanar coupling by decreasing the c-axis length, without significantly disturbing the intraplanar superconductivity. Our results directly show the relationship between lattice spacing and the irreversibility line in Bi(2)Sr(2)CaCu(2)O(8+delta), and demonstrate the potential for a dramatic reduction in the flux motion.