We have studied the magnetism of the half-doped charge ordered manganite ${\mathrm{YBaMn}}_2{\mathrm{O}}_6$. A formation of ferromagnetic plaquettes of four Mn atoms in the charge ordered phase below $T_{\mathrm{CO}}\sim 480\mathrm{K}$ is inferred from high temperature magnetic susceptibility data and the magnetic structure, as determined by neutron powder diffraction at $T=1.5\mathrm{K}$. The results indicate that new fourfold Mn paramagnetic units form between $T_N<T<T_{\mathrm{CO}}$, and that they order in a noncollinear mode below $T_N=190\mathrm{K}$. The magnetism of ${\mathrm{YBaMn}}_2{\mathrm{O}}_6$ is consistent with what is expected from the Zener polarons ordering picture of the charge ordering phenomenon in manganites [A. Daoud-Aladine et al., Phys. Rev. Lett. 89, 097205 (2002)].

• Received 22 August 2007

DOI:https://doi.org/10.1103/PhysRevLett.101.166404