Nominal kagome antiferromagnetic Mn₃Sn: effects of excess Mn and its novel synthesis method

The antiferromagnetic (AFM) Weyl semimetal Mn₃Sn has attracted significant interest due to its intriguing topological and transport properties. However, the reproducibility of experimental results has been limited, potentially stemming from the thermodynamically stable Mn_3+xSn_1−x phase, where excess Mn substitutes at Sn sites and alters its intrinsic helical ordering. In this study, we present a Bi flux-assisted recrystallization method for synthesizing high-quality nominal Mn₃Sn single crystals. Our approach yields stoichiometric and homogeneous samples with the largest residual resistivity ratio (RRR > 23) and sharper magnetic phase transitions, confirming their high purity. While the triangular AFM phase at room temperature is independent of sample quality, the helical magnetic ordering exhibits strong quality dependence, with additional helical phases emerging between 250 K and 280 K. At low temperatures, the system retains a semimetallic nature, as evidenced by the lower Sommerfeld coefficient (γ), differential conductance (dI/dV) spectra, and magnetoresistance measurements. These findings highlight the interplay between chemical composition and magnetic phase transitions in Mn₃Sn and establish a direct link between its helical ordering and electronic structure tuning. Our results not only provide a pathway for producing high-quality Mn₃Sn single crystals but also offer a valuable platform for exploring unresolved aspects of its helical phases and potential applications in AFM spintronics.