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 YBaMn2O6. A formation of ferromagnetic plaquettes of four Mn atoms in the charge ordered phase below T-CO similar to 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 YBaMn2O6 is consistent with what is expected from the Zener polarons ordering picture of the charge ordering phenomenon in manganites [A. Daoud-Aladine , Phys. Rev. Lett. 89, 097205 (2002)].