Flux pinning and magnetic anisotropy in neutron irradiated Hg-Ba-Ca-Cu-O

Magnetic studies are performed on randomly oriented and aligned polycrystalline samples of HgBa/sub 2/CaCu/sub 2/O/sub 6+x/ (Hg-1212) and HgBa/sub 2/Ca/sub 2/Cu/sub 3/O/sub 8+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/sub c/ with temperature is much slower than the decay of their single-layered counterpart, Hg-1201. Measurements of aligned Hg-1212 revealed that the dependence of J/sub c/ on field orientation is relatively weak and the irreversible area in the H-T plane is much wider than other high temperature superconductors. Although neutron 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.<
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