Peak effect of critical current density in stoichiometric SmBa2Cu3Oy sample

A fully oxygenated stoichiometric SmBa2Cu3Oy sample showed a weak but distinct peak effect in the magnetization versus applied magnetic field curve at 40 K. The peak was located at about 2 T. The oxygen content of this sample was determined at y=7.01±0.05. Thus, it is unlikely that the peak observed for this sample was caused by ordering of oxygen atoms. When the sample was pulverized and annealed in oxygen gas at 800°C, part of SmBa2Cu3Oy apparently decomposed into BaCuO2 and CuO in the part of thin surface layer (less that ∼30 nm thickness) of the powder grains, according to TEM observations and EDX analyses. This would mean that the concentration of Sm became higher than the stoichiometric value in the interior of the grain to form Sm-rich region. The observed weak peak effect may be caused by the Sm-rich region inside the grains, since some Sm-rich Sm1+xBa2−xCu3Oy samples prepared by an oxygen controlled melt growth (OCMG) process were reported to show a peak effect.