Optimization of Magnetic Stability in Nb₃Sn Materials Near Stoichiometric Composition

Using a solid-state reaction method starting with Nb and Nb<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub>Sn<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> powders, we have synthesized bulk Nb<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>Sn 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 in samples with three different Sn contents. We found that the highest <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_c</i> is located 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 Nb<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>Sn materials are investigated through magnetization measurements, and significant suppression to flux jumps was found in samples with slightly higher Sn content (Sn content ≈25.6%) and better compactness and grain refinement.