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

Zener Polaron (ZP) ordering [1] provides a still polemic [2] and elusive interpretation of the charge ordering (CO) phenomenon in A site disordered half doped (A$_{1/2}$Ca$_{1/2}$) MnO$_3$, which is classically pictured by the Goodenough model (GM) of Mn$^{3+}$ and Mn$^{4+}$ CO [3,4]. ZP ordering considers instead the ordering of pre-formed ferromagnetic Mn pairs sharing an charge and keeping Mn in a Mn$^{+3.5}$ valence state. The recently synthesized A site cation ordered ABaMn$_2 $O$_6$ were shown to not present the generic magnetic CE state found of (A$_{1/2}$Ca$_{1/2}$)MnO$_3$ [5]. We present our magnetic structure determination of YBaMn$_2$O$_6$: the non- collinear magnetic order obtained unexpectedly reveals ferromagnetic plaquettes of four Mn attributable to larger 4-Mn ZPs, whose presence additionally fits very well the effective paramagnetic moments inferred from susceptibility measurements. The results unambiguously reveal the possible existence of ZP ordering variant in charge ordered manganites. [1] A. Daoud-Aladine et al., Phys. Rev. Lett. 89, 097205 (2002) [2] S. Grenier et al., Phys. Rev. B 69, 134419 (2004) [3] J. B. Goodenough, Phys. Rev. 100, 564 (1955) [4] P.G. Radaelli et al., Phys. Rev. B, 55, 3015 (1997) [5] T. Arima et al., Phys. Rev. B 66, 140408 (2002)