Morphology and low AC field magnetic susceptibility of Y(Ba2-x,Mnx)Cu3O7

Bulk YBCO samples with various Mn2+ doping concentrations (x=0.01, 0.15, 0.17, 0.19, 0.21, and 0.30) were prepared. The behavior of the intragranular and intergranular responses in the fundamental complex susceptibility (χ'+iχ'') under varying low AC field amplitude in the range of 0.08mT to 0.13mT was investigated. The temperature dependence of the AC magnetic susceptibility shows that samples with higher doping concentration were highly influenced by the change of the AC magnetic field amplitude. Double peak in the χ'' and shoulder transition in χ’ were observed. These features disappear as the doping concentration increases. It was also found that the field-independent region at the onset of diamagnetic transition in χ' broadens. Relating this with the degree of granularity of the samples observed in the scanning electron microscope images, the decrease in grain size results to the longer transition width. This behavior is possibly associated with the suppressed diamagnetic shielding abilities in the grain periphery. Therefore, Mn2+ deteriorates the superconducting properties of the grains.