The superconducting properties of YBa₂(Cu_1-xM_x)₃O₇ for M=Zn and Ni

Transverse and zero-field μSR measurements were made on YBa₂(Cu_1-xNi_x)₃O_7-y with x=0.1 and 0.2, and YBa₂(Cu_1-xZn_x)₃O_7-y with x=0.03, 0.06, 0.1, and 0.16, where y≈0.1. Since doping may lead to magnetic ordering this was searched for with both zero and transverse field μSR, but no evidence was found over the temperature range studied: 10-100 K. However, depolarization rates as functions of temperature were obtained, and the low temperature values of these are σ=3.2 μs^-1.1.6μs^-1, and 1 μs^-1 for x=0.01, and 0.2 Ni, respectively, and σ=0.8 μs^-1, 0.75 μs^-1, 0.65 μs^-1, and 0.4 μs^-1 for x=0.03, 0.06, 0.1, and 0.16 Zn, respectively. Estimates for the effect of decreasing electron concentration for Zn are made, but these alone do not account for the drop in σ. Estimates for the effect of scattering on λ and hence σ are made. The reduction in σ for Ni dopant is in surprisingly good agreement with these estimates. For Zn the order of magnitude is correct, but the relative lack of further change in σ after the effect of the first 0.03 addition seems to imply a saturation of the effect of scattering.