Manganite charge and orbitally ordered and disordered states probed by Fe substitution into Mn site in image, image and image (image, Gd, Sm, Nd, Pr, La)

The layered manganese oxides LnBaMn1.96Fe0.04OyLnBaMn1.96Fe0.04Oy (Ln=YLn=Y, Gd, Sm, Nd, Pr, La) have been synthesized for y=5,5.5y=5,5.5 and 6. In the oxygen-saturated state (y=6)(y=6) they exhibit the charge and orbital order at ambient temperature for Ln=YLn=Y, Gd, Sm, but unordered egeg-electronic system for Ln=LaLn=La, Pr, Nd. Fourfold increase of quadrupole splitting was observed owing to the charge and orbital ordering. This is in agreement with the jumplike increase in distortion of the reduced perovskite-like cell for the charge and orbitally ordered manganites compared to the unordered ones. Substitution of 2% of Mn by Fe suppresses the temperatures of structural and magnetic transitions by 20–50 K. Parameters of the crystal lattices and the room-temperature Mössbauer spectra were studied on 40 samples whose structures were refined within five symmetry groups: P4/mmmP4/mmm, P4/nmmP4/nmm, PmPm-3m3m, IcmaIcma and P2/mP2/m. Overwhelming majority of the Fe species are undifferentiated in the Mössbauer spectra for most of the samples. Such the single-component spectra in the two-site structures are explained by the preference of Fe towards the site of Mn(III) and by the segmentation of the charge and orbitally ordered domains.