Block magnetism coupled with local distortion in the iron-based   spin-ladder compound BaFe2Se3
  Magnetism in the insulating BaFe$_2$Se$_3$ 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 $T_{\rm N}\sim 255$ K. The transition is obscured by bulk properties. Magnetic moments ($\parallel a$) 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. 
Yusuke Nambu, Kenya Ohgushi, Shunpei Suzuki, Fei Du, Maxim Avdeev,   Yoshiya Uwatoko, Koji Munakata, Hiroshi Fukazawa, Songx...
cond-mat.str-el cond-mat.supr-con