FLUX-PINNING AND MAGNETIC-ANISOTROPY IN NEUTRON-IRRADIATED HG-BA-CA-CU-O

Magnetic studies are performed on randomly oriented and aligned polycr ystalline samples of HgBa2CaCu2O6+x (Hg-1212) and HgBa2Ca2Cu3O8+x (Hg- 1223). The measurements of magnetic hysterisis and magnetic relaxation confirmed the existence of a strong surface barrier. The decay of the critical current density J(c) with temperature is much slower than th e decay of their single-layered counterpart, Hg-1201. Measurements of aligned Hg-1212 revealed that the dependence of J(c) on field orientat ion is relatively weak and the irreversible area in the H-T plane is m uch wider than other high temperature superconductors. Although neutro n irradiation only enhances the critical current values moderately and severely suppresses the surface pinning, neutron irradiation improves all of the magnetic properties mentioned above, and at T = 100 K, the hysteresis loop remains open up to H = 6 kG.