  We demonstrate the presence of ferromagnetic (FM) fluctuations in the
superconducting and non-superconducting heavily overdoped regimes of
high-temperature superconducting copper oxides, using
(Bi,Pb)_2_Sr_2_CuO_6+delta_ (Bi-2201) single crystals. Magnetization curves
exhibit a tendency to be saturated in high magnetic fields at low temperatures
in the heavily overdoped crystals, which is probably a precursor phenomenon of
a FM transition at a lower temperature. Muon spin relaxation detects the
enhancement of spin fluctuations at high temperatures below 200 K.
Correspondingly, the ab-plane resistivity follows a 4/3 power law in a wide
temperature range, which is characteristic of metals with two-dimensional FM
fluctuations due to itinerant electrons. As the Wilson ratio evidences the
enhancement of spin fluctuations with hole doping in the heavily overdoped
regime, it is concluded that two-dimensional FM fluctuations reside in the
heavily overdoped Bi-2201 cuprates, which is probably related to the decrease
in the superconducting transition temperature in the heavily overdoped
cuprates.
