ANISOTROPY OF THE MAGNETIC-PROPERTIES OF C-AXIS-ALIGNED HGBA2CA2CU3O8+DELTA POWDERS

We report the anisotropy of magnetic properties of c-axis-aligned HgBa 2Ca2Cu3O8+delta powders embedded in epoxy. The alignment was done by a pplying a 7-tesla magnetic field at room temperature. The temperature dependence of the anisotropic ratio, chi(parallel-to c)(T)/chi(perpend icular-to c)(T), in the superconducting state was derived from data me asured with zero-field cooling and field cooling for both parallel and perpendicular to the c axis at 30 G. The anisotropic ratio of about 3 .05 was obtained at 5 K. The magnetization hysteresis loops M(H) were measured up to +/-5 tesla at various temperatures. The magnetic flux i rreversibility, calculated from M (H) curves, decreases exponentially with increasing magnetic field, and the critical current density was e stimated using the Bean model (i.e., J(c) = 32DELTAM/d, where d was ta ken to be the average particle diameter of 2.5 mum). J(c)(H parallel-t o c) at 5 K in 0.5 tesla was found to be approximately 10(7) A/cm2. Th e anisotropic ratios of the magnetic flux irreversibilities decrease r apidly with increasing magnetic field up to 0.5 tesla but decrease slo wly in the field region higher than 0.5 tesla; the decrease of the rat ios indicates that more significant activation of fluxoid in the c dir ection reduces DELTAM(H parallel-to c) rapidly. The data of DELTAM(par allel-to c) and DELTAM(perpendicular-to c) in the low-temperature regi on below 30 K can be fitted by the exponential function DELTAM(T) = a exp(-T/T0) with T0 = 14.2 K, a=3.75 emu/g for H parallel-to c and T0 = 18.2 K, a = 2.50 emu/g for H perpendicular-to c at 4 tesla, and in th e high-temperature region above 30 K, the simple power law DELTAM(T) = b(1-T/T(c))n was observed with n=6.42, b=32.9 emu/g for H parallel-to c and n = 4.65, b = 11.2 emu/g for H perpendicular-to c at 0.5 tesla.