The magnetization of very dilute Cu:Fe alloys contains one term proportional to $c$ due to the isolated impurities and another proportional to $c^2$ which is attributed to nearly magnetic or magnetic pairs. The susceptibility of the isolated iron atoms follows a Curie-Weiss law $C{(T+T_k)}^{-1\mathrm{}}$ with $T_k=29\mathrm{}$ K well below $T_k$. The $c^2$ term which is nearly saturated in 60 kOe at 1.3 K is responsible for the important temperature dependence of the initial susceptibility below $T_k$.

• Received 27 July 1970

DOI:https://doi.org/10.1103/PhysRevLett.25.867