Ferromagnetic Particles in a Type-II Superconductor

Abstract

A dispersion of fine, single‐domain, iron particles in a superconducting Hg‐13% In alloy is found to produce considerably magnetic hysteresis that is dependent on the sense of the applied field. When the applied field is parallel to the remanent particle magnetization, and particles attract and pin flux threads, the observed hysteresis is always larger than in the antiparallel case, where particles repel flux threads. Significant sense‐dependent properties have been observed for particles from 20 to 200 Å in diameter, and for volume fractions from 0.01% to 1%. The results demonstrate the effectiveness of ferromagnetic particles in increasing superconducting critical currents, the superiority of attractive centers over repulsive ones, and the possibility of ``directional superconductors'' whose properties depend on the sense of the applied magnetic field.