Ferromagnetic Fluctuations in the Heavily Overdoped Regime of Single-Layer High-T_c Cuprate Superconductors

To investigate proposed ferromagnetic fluctuations in the so-called single-layer Bi-2201 and La-214 high-T_c cuprates, we performed magnetization and electrical resistivity measurements using single-layer Tl-2201 cuprates Tl₂Ba₂CuO_6+δ and La-214 La_2-SrCuO₄ in the heavily overdoped regime. Magnetization of Tl₂Ba₂CuO_6+δ and La_2-SrCuO₄ exhibited the tendency to be saturated in high magnetic fields at low temperatures, suggesting the precursor behavior toward the formation of a ferromagnetic order. It was found that the power of temperature n obtained from the temperature dependence of the electrical resistivity is ~4/3 and ~5/3 for Bi-2201 and La_2-SrCuO₄, respectively, and is ~4/3 at high temperatures and ~5/3 at low temperatures in Tl₂Ba₂CuO_6+δ. These results suggest that two- and three-dimensional ferromagnetic fluctuations exist in Bi-2201 and La_2-SrCuO₄, respectively. In Tl₂Ba₂CuO_6+δ, it is suggested that the dimension of ferromagnetic fluctuations is two at high temperatures and three at low temperatures, respectively. The dimensionality of ferromagnetic fluctuations is understood in terms of the dimensionality of the crystal structure and the bonding of atoms in the blocking layer.