Magnetic Impurity Pairs in Dilute Cu(Fe) Alloys at Very Low Temperatures

The temperature-dependent static magnetization of several dilute Cu(Fe) alloys with Fe concentrations between 102 and 478 ppm has been measured infields between 1 and 200 Oe and at temperatures between 9 mK and 0.4 K. At higher temperatures and in small fields, the magnetization displays the following concentration, field, and temperature dependences: M proportional to c(2)HT(-2/3). At lower temperatures, magnetic ordering is observed. These results are interpreted in terms of the behavior of pairs of impurities acting as individual entities. They are quite likely correlated with the anomalous low field, low-temperature observations made in previous measurements of the resistivity and specific heat of the Cu(Fe) system.