Optimization of Magnetic Stability in Nb3Sn Materials Near Stoichiometric Composition

Using a solid-state reaction method starting with Nb and Nb6Sn5 powders, we have synthesized bulk Nb3Sn samples with uniformly distributed Sn contents of 24%, 25% and 25.6%. Among them, the sample with Sn content = 25% may go through a structural phase transition from cubic to tetragonal structure at a low temperature of 43 K. The X-ray diffraction and resistivity measurements show systematic changes of the three different kinds of samples. We found that the highest Tc locates in the sample with exactly stoichiometric composition (Sn content = 25%), which may be due to the tetragonal structure. In addition, properties of flux jumps under various physical conditions in Nb3Sn materials are investigated through magnetization measurements, significant suppression to flux jumps were found in samples with slightly higher Sn content (Sn content ≈ 25.6%), and better compactness as well as grain refinement.