Manganite charge and orbitally ordered and disordered states probed by Fe substitution into Mn site in LnBaMn1.96Fe0.04O5, LnBaMn1.96Fe0.04O6 and LnBaMn1.96Fe0.04O5.5 (Ln=Y, Gd, Sm, Nd, Pr, La)

摘要

The layered manganese oxides LnBaMn1.96Fe0.04Oy (Ln=Y, Gd, Sm, Nd, Pr, La)have been synthesized for y=5, 5.5 and 6. In the oxygen-saturated state (y=6)they exhibit the charge and orbital order at ambient temperature for Ln=Y, Gd,Sm, but unordered eg-electronic system for Ln=La,Pr,Nd. Fourfold increase ofquadrupole splitting was observed owing to the charge and orbital ordering.This is in agreement with the jumplike increase in distortion of the reducedperovskite-like cell for the charge and orbitally ordered manganites comparedto the unordered ones. Substitution of 2 percents of Mn by Fe suppresses thetemperatures of structural and magnetic transitions by 20 to 50 K. Parametersof the crystal lattices and the room-temperature M\"{o}ssbauer spectra werestudied on forty samples whose structures were refined within five symmetrygroups: P4/mmm, P4/nmm, Pm-3m, Icma and P2/m. Overwhelming majority of the Fespecies are undifferentiated in the M\"{o}ssbauer spectra for most of thesamples. Such the single-component spectra in the two-site structures areexplained by the preference of Fe towards the site of Mn(III) and by thesegmentation of the charge and orbitally ordered domains.