New magnetic structures in novel and conventional manganites

The determination of the magnetic structures of manganites has always been at the root of their fundamental understanding [1]. We studied the magnetic structures of half-doped charge ordered manganites that are either show the prototype [1] CE-type magnetic structure (Pr$_{1/2}$Ca$_{1/2}$MnO$_{3}$), or variants of this order (YBaMn$_2$O$_{6}$ [2] and Pr$_{0.6}$Ca$_{0.4}$MnO$_{3} $) with neutron diffraction. The study of Pr$_{1/2}$Ca$_{1/2}$MnO$_{3}$ (ILL, France) is the first ever done on a single crystal and it essentially confirms the pioneering picture [1], whereas the NPD studies of YBaMn$_2$O$_{6}$ [2] (PSI, Switzerland) and Pr$_{0.6}$Ca$_{0.4}$MnO$_{3}$ [3] (ISIS, UK), give two unprecedented results. The YBaMn$_2$O$_{6}$ magnetic structure corroborates the hotly debated ordering of Zener Polarons [4], and high resolution NPD data evidence a new spin reorientation transition around T$\sim$20K far below its TN$\sim170K$ in Pr$_ {0.6}$Ca$_{0.4}$MnO$_{3}$ [3] that has so far only been vaguely observed. We will discuss the consequences that these results have on the still hotly debated understanding of the connection between charge/orbital and spin orderings in the manganites. [1] Wollan, E.O. and Koehler, W.C. Rev. 100, 545 (1955) [2] A. Daoud-Aladine et al., Phys. Rev. Lett.: 101 166404 (2008) [3] A. Daoud-Aladine et al., unpublished [4] M. Coey Nature 430, 155-157 (8 July 2004)