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 Tl 2 Ba 2 CuO 6+δ and La-214 La 2- x Sr x CuO 4 in the heavily overdoped regime. Magnetization of Tl 2 Ba 2 CuO 6+δ and La 2- x Sr x CuO 4 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- x Sr x CuO 4 , respectively, and is ~4/3 at high temperatures and ~5/3 at low temperatures in Tl 2 Ba 2 CuO 6+δ . These results suggest that two- and three-dimensional ferromagnetic fluctuations exist in Bi-2201 and La 2- x Sr x CuO 4 , respectively. In Tl 2 Ba 2 CuO 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.