Vibrational anisotropy and quadrupole interactions of Fe substituted onto the Mn site of the charge and orbitally ordered and disordered layered manganites LBaMn_(1.96)Fe_(0.04)O_5 and LBaMn_(1.96)Fe_(0.04)O_6 (L = Y, Gd, Sm, Nd, Pr, and La)

摘要

A-site-ordered manganites LBaMn_(1.96)Fe_(0.04)O_5 and LBaMn_(1.96)Fe_(0.04)O_6 are investigated by x-ray full-profile diffraction and Mossbauer spect oscopy. 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 Mossbauer spectra. Combined effects of preferred orientation and vibrationaf anisotropy on the line-area asymmetry of Mossbauer doublet are analyzed. Constructive and destructive interference between the effects of texture and vibrational anisotropy is observed in LBaMn_(1.96)Fe_(0.04)O_6 and LBaMn_(1.96)Fe_(0.04)O_5 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 "O_5" and "O_6" series, except LaBaMn_(1.96)Fe_(0.04)O_5. However, the short-range COO persists to be observed in magnetization and in x-ray patterns.