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

Abstract

The layered manganese oxides Ln BaMn 1.96 Fe 0.04 O y ( 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 e g -electronic system for Ln = 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: P 4 / mmm , P 4 / nmm , Pm - 3 m , Icma and P 2 / 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.