Vibrational anisotropy and quadrupole interactions of Fe substituted onto the Mn site of the charge and orbitally ordered and disordered layered manganites LBaMn1.96Fe0.04O5 and LBaMn1.96Fe0.04O6 ( L=Y , Gd, Sm, Nd, Pr, and La)

A -site-ordered manganites LBaMn_1.96Fe_0.04O₅ and LBaMn_1.96Fe_0.04O₆ are investigated by x-ray full-profile diffraction and Mössbauer 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 Mössbauer spectra. Combined effects of preferred orientation and vibrational anisotropy on the line-area asymmetry of Mössbauer doublet are analyzed. Constructive and destructive interference between the effects of texture and vibrational anisotropy is observed in LBaMn_1.96Fe_0.04O₆ and LBaMn_1.96Fe_0.04O₅ , respectively. Both series of the manganites show the main axis of electric-field gradient perpendicular to layers (V_zz∥c) with V_zz>0 in oxygen-poor series and V_zz<0 in oxygen-rich series. Charge-orbital order (COO) melting around Fe dopants explains the single-site spectra observed for several Ln in both “ O₅ ” and “ O₆ ” series, except LaBaMn_1.96Fe_0.04O₅ . However, the short-range COO persists to be observed in magnetization and in x-ray patterns.