Ferromagnetic signal and unconventional Kondo-like effect in the superconducting Y_(1-x)Pr_xBa_2Cu_3O_(7-δ)systems

摘要

Electrical and magnetic properties were studied for the Y_(1-x)Pr_xBa_2Cu_3O_(7-δ) superconductors with x=0.44-0.48, which was located near the antiferromagnetic (AFM) and superconducting (SC) phase boundaries. An unconventional Kondo-like effect is observed below T_c for x=0.48, where the value of the resistivity minimum p_(min) increases with increasing magnetic field H. The transition temperature T_(min) first increases and then decreases with increasing field strength. Magnetic measurements show that a small fraction of FM phase appears and coexists with the SC and AFM phases. We discuss these findings from the viewpoints of Kondo scattering and electron-electron interaction, and found that the resistivity minimum below T_c is mainly due to the Kondo scattering. The Kondo scattering is identified as SC phase coexisting with AFM and FM clusters, which is as the Kondo singlets resulting from Pr substitution. This phase-separated state is unstable against the magnetic field which suppresses the SC phase and restores the single Kondo peak at low temperatures.