  Magnetic hyperfine field at Cu isotopes as impurities in Fe were recently
measured at low temperature. A model to explain these experimental results is
proposed. The diluted Cu impurities in the ferromagnetic Fe host are described
by an extension of the Daniel-Friedel model, including the next neighbor
perturbation. In order to account for the available experimental data in Cu
isotopes with atomic masses $A$ = 59, 67, 69 and 71 as impurity, we needed to
incorporate the Cu anomaly volume in the effective charge to be screened and in
the self-consistent procedures.
