\textbf{Magnetic structure and its role in the possible Weyl state in topological semimetal Sr}$_{\mathbf{1-y}}$\textbf{Mn}$_{\mathbf{1-z}}$\textbf{Sb}$_{\mathbf{2}}_{\, \, }$(0\textless y,z\textless 0.1)

Very recently, Liu et al (\textit{arxiv.org/pdf/1507.07978, (2015)}) discovered the first magnetic topological semimetal Sr$_{1-y}$Mn$_{1-z}$Sb$_{2\, \, }$(0\textless y,z\textless 0.1), in which a possible Weyl state arising from time reversal symmetry breaking is expected. However, the origin of ferromagnetic (FM) behavior of this material has not been clarified. By employing the neutron diffraction at the four-circle diffractometer HB3A, HFIR, we found a long-range FM order with Mn moments along $b$-axis below $T_{C}=$565 K, followed by another magnetic transition to a canted $C$-type antiferromagnetic (AFM) order at $T_{FM-AFM}=$ 304 K. In the canted $C$-type AFM state, the Mn moments are aligned with the $a$-axis along with a canting toward the $b$-axis, leading to a net FM moment lying along the$ b-$axis. The Mn moments along the $a-$ and $b$-axes at 5 K are found to be 3.789(3) and 0.741(4) \textmu $_{B}$, respectively. The discovered FM order in Sr$_{1-y}$Mn$_{1-z}$Sb$_{2}$, either the FM ordering at 304\textless $T$\textless 565 K or the FM component of the canted AFM order for $T$\textless 304 K, is sufficient to break time-reversal symmetry likely creating a Weyl semimetal.