Block magnetism coupled with local distortion in the iron-based spin-ladder compound BaFe2Se3

Magnetism in the insulating BaFe2Se3 was examined through susceptibility, specific heat, resistivity, and neutron diffraction measurements. After formation of a short-range magnetic correlation, a long-range ordering was observed below T-N similar to 255 K. The transition is obscured by bulk properties. Magnetic moments (parallel to a) are arranged to form a Fe-4 ferromagnetic unit, and each Fe-4 stacks antiferromagnetically. This block magnetism is of the third type among magnetic structures of ferrous materials. The magnetic ordering drives unusually large distortion via magnetoelastic coupling.