  We investigated Fe-substitution effects on ferromagnetic fluctuations in the
superconducting overdoped and non-superconducting heavily overdoped regimes of
the Bi-2201 cuprates by the magnetization and electrical-resistivity
measurements. It was found that the spin-glass state was induced at low
temperatures by the Fe substitution. The Curie constant and the effective Bohr
magneton, estimated from the magnetic susceptibility, as well as the
dimensionality of the ferromagnetic fluctuations from the resistivity, suggest
the enhancement of the ferromagnetic fluctuations owing to the Fe substitution.
A ferromagnetic spin-cluster model is proposed in the heavily overdoped regime
of Bi-2201, while an antiferromagnetic spin-cluster model has been proposed in
the overdoped regime of Bi-2201 [Hiraka et al., Phys. Rev. B 81, 144501
(2010)].
