Unusual Magnetic Behavior in BaMn$_{2}$Sb$_{2}$

We have performed experimental investigation on magnetic properties of BaMn$_{2}$Sb$_{2}$ single crystals grown using the flux method. X-ray diffraction measurements show that BaMn$_{2}$Sb$_{2}$ forms the ThCr$_{2}$Si$_{2}$-type tetragonal structure at room temperature. Single crystal neutron diffraction refinement indicates the G-type antiferromagnetic (AFM) ordering below T$_{N}$. However, the transition temperature T$_{N}$ is strongly sample dependent, varying from 280 K to 800 K. At a fixed temperature and magnetic field, the DC magnetization is also strongly time dependent. These results indicate that the magnetic properties of BaMn$_{2}$Sb$_{2}$ are extremely sensitive to sample and measurement history. Possible origins will be discussed.