Magnetism in SmBaMn
2O
5 was investigated on a single crystal by magnetic and
neutron diffraction measurements. This is an oxygen deficient
perovskite with a layered ordering of Sm and Ba cations. Mn atoms are coordinated with five oxygens forming a square pyramid and they are ordered in a checkerboard pattern of expanded-compressed pyramids in the ab-plane. The neutron diffraction study revealed a ferrimagnetic ordering of Mn moments below T
N=134 K. Macroscopic measurements reveal a very anisotropic behavior.