Surface barriers, irreversibility line, and pancake vortices in an aligned HgBa2Ca2Cu3O8 superconductor

The irreversible magnetic properties of a magnetically aligned HgBa2Ca2Cu3O8 superconductor have been investigated as a function of temperature and magnetic field, for both Hc axis and H ab plane. Experimental results for the magnetic hysteresis M, the field of first flux penetration Hp, and the irreversibility line with H 5f aree well described by recent theory [L. Burlachkov et al., Phys. Rev. B 50, 16 770 (1994)] for thermally activated penetration of a surface barrier by pancake vortices. Near 85 K, the system crosses over from two-dimensional to three-dimensional line vortices, from which we extract estimates for the mass anisotropy parameter.