Zener Polaron Ordering Variants Induced by A-Site Ordering in Half-Doped Manganites

We have studied the magnetism of the half-doped charge ordered manganite YBaMn 2 O 6 . A formation of ferromagnetic plaquettes of four Mn atoms in the charge ordered phase below T co ∼ 480 K is inferred from high temperature magnetic susceptibility data and the magnetic structure, as determined by neutron powder diffraction at T = 1.5 K. The results indicate that new fourfold Mn paramagnetic units form between T N < T < T co , and that they order in a noncollinear mode below T N = 190 K. The magnetism of YBaMn 2 O 6 is consistent with what is expected from the Zener polarons ordering picture of the charge ordering phenomenon in manganites.