Surface resistance at microwave frequencies in transition metal ion substituted yttrium barium copper oxide superconductors

The temperature dependence of the surface resistance is investigated in polycrystalline yttrium barium copper oxide samples in which 2% of Cu is replaced with Fe, Mn, Co, or Ni. The superconducting transition temperature, determined from ac susceptibility measurements, varies from a maximum of 93K for the undoped sample to a minimum of 89.5K for the sample with Ni. A resonant cavity technique is used to determine the surface resistance at x-band frequencies over the temperature range 77 to 100K. The data show a relatively large microwave resistance in the normal and superconducting states for samples containing Fe and Co. The superconducting energy gap is determined from the high frequency resistance data. (orig.)