LAUSR

We investigated the effects of Fe substitution on ferromagnetic fluctuations in the superconducting overdoped and non-superconducting heavily overdoped regimes of Bi-2201 cuprates by 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 magnetic susceptibility, as well as the dimensionality of the ferromagnetic fluctuations from the resistivity, suggest the enhancement of the ferromagnetic fluctuations caused by the Fe substitution. A ferromagnetic spin-cluster model is proposed for the heavily overdoped regime of Bi-2201, whereas an antiferromagnetic spin-cluster model has been proposed for the overdoped regime of Bi-2201 [Hiraka et al., Phys. Rev. B 81, 144501 (2010)].