Abstract
$A$-site-ordered manganites $L{\text{BaMn}}_{1.96}{\text{Fe}}_{0.04}{\text{O}}_{5}$ and $L{\text{BaMn}}_{1.96}{\text{Fe}}_{0.04}{\text{O}}_{6}$ are investigated by x-ray full-profile diffraction and M\ossbauer spectroscopy. Powder samples were oriented with preferred orientation of platy crystallites in the plane of sample surface. March-Dollase function of preferred orientation was employed in analyzing both the Rietveld patterns and the M\ossbauer spectra. Combined effects of preferred orientation and vibrational anisotropy on the line-area asymmetry of M\ossbauer doublet are analyzed. Constructive and destructive interference between the effects of texture and vibrational anisotropy is observed in $L{\text{BaMn}}_{1.96}{\text{Fe}}_{0.04}{\text{O}}_{6}$ and $L{\text{BaMn}}_{1.96}{\text{Fe}}_{0.04}{\text{O}}_{5}$, respectively. Both series of the manganites show the main axis of electric-field gradient perpendicular to layers $({V}_{zz}\ensuremath{\parallel}c)$ with ${V}_{zz}g0$ in oxygen-poor series and ${V}_{zz}l0$ in oxygen-rich series. Charge-orbital order (COO) melting around Fe dopants explains the single-site spectra observed for several Ln in both ``${\text{O}}_{5}$'' and ``${\text{O}}_{6}$'' series, except ${\text{LaBaMn}}_{1.96}{\text{Fe}}_{0.04}{\text{O}}_{5}$. However, the short-range COO persists to be observed in magnetization and in x-ray patterns.
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