Magnetic field alignment of high-Tc superconductorsRBa2Cu3O7–δ (R=rare earth)

Finely ground powders ofRBa₂Cu₃O_{7 - d} (R=Y, Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb) have been mixed at dilute 3%-by-volume concentrations into epoxy matrices which were then allowed to harden in applied magnetic fieldsH_A=18 kOe. X-ray diffractometry studies and 4.3 K measurements of supercurrent-induced magnetization hysteresis?M are interpreted as indicating at least partial alignment of single-crystal-grain c-axes (1) parallel toH_A forR=Y, Nd, Sm, Dy, Ho (as earlier found by Farrell et al. forR=Y), and (2) perpendicular toH_A forR=Eu, Er, Tm, Yb. With a few exceptions (Y, Sm, Eu) the alignment direction correlates with the sign of the second-order Stevens factora_J of the crystalline electric field Hamiltonian in the manner suggested by Livingston et al. For the best aligned specimens (Ho, Dy) critical current densitiesJ_c (4.3 K, 5 kOe) for individual grains are estimated from?M and the Bean model to be of order 10⁷ A/cm² for the measuring fieldH parallel to the original alignment fieldH_A, and of order 10⁶ A/cm² forH perpendicular toH_A.