muSR study of the Fe-substitution effects on ferromagnetic fluctuations in heavily overdoped Bi-2201 cuprates

Recently, it has been suggested in heavily hole-doped high-Tc cuprates that ferromagnetic (FM) fluctuations exist and compete with the superconductivity. Moreover, we have found that 5% Fe substitution for Cu in heavily overdoped Bi-2201 cuprates brings about the coexistence of enhanced FM fluctuations and a spin-glass state of Fe spins. The purpose of this proposed study is to clarify the Fe-induced magnetic states in Fe-substituted Bi-2201 cuprates, changing the Fe content systematically, from muSR measurements down to 0.3 K. This study combined with our electrical-resistivity and magnetic-susceptibility measurements would provide significant information on the nature of the FM and spin-glass states in the heavily overdoped cuprates, leading to the understanding of the superconductivity and FM fluctuations.