Oxygen-free Copper at 4 K: Resistance and magnetoresistance

Oxygen-free copper is the most common material used for stabilizing practical superconductors. This type of copper may show residual resistance ratios (RRR) that vary from 50 to 700 in the full soft condition. Knowledge of the exact RRR value is often essential for optimum system design. We have investigated the effect of stress, temper, and reanneal on the RRR and magnetoresistance of several hundred samples of oxygen-free copper from many sources. In this paper we describe the program and present a sampling of the results obtained to date.