Magnetic field alignment of high-T c superconductorsRBa2Cu3O7?? (R=rare earth)

Abstract

Finely ground powders ofRBa2Cu3O7 − δ (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 hysteresisΔM 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 factorα 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 fromΔM 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.