Structure, phase transitions, 55Mn NMR, 57Fe Mössbauer studies and magnetoresistive properties of [formula omitted

Abstract

The influence of substitution of Fe ions for manganese on the structure, phase transitions, magnetoresistance, 55Mn NMR and 57Fe Mössbauer spectra in the ceramic La0.6Sr0.3Mn1.1−xFexO3 (x=0–0.15) samples has been studied by X-ray diffraction, electron microscopy, magnetic, 55Mn NMR and 57Fe Mössbauer methods. The real rhombohedral perovskite structure (R3¯c) is established to contain the different valence manganese ions (Mn3+ and Mn4+), anion and cation vacancies as well as nanostructural clusters with Mn2+ located in the A-sites. Temperature dependences of the a lattice parameter, a(T), demonstrate the anomalies near the Curie temperature, Tc. Wide asymmetric 55Mn NMR spectra confirm the high frequency electron double exchange between Mn3+ and Mn4+ ions and irregularity of their surrounding by other ions and defects. According to the Mössbauer spectroscopy data, Fe3+ ions (~80%) substitute for Mn3+ and partially Mn4+ in the B-positions. The rest of Fe3+ (Fe2+) ions and clusters with Mn2+ are located in the A-positions. The temperatures of metal–semiconductor and ferromagnet–paramagnet phase transitions are reduced with increasing x, and the magnetic irregularity increases due to the weakening high-frequency Mn3+↔Mn4+ double exchange by Fe3+ ions. The amount of ferromagnetic phase is also reduced. The anomalous hysteresis is interpreted as a result of anisotropy of exchange interaction between the ferromagnetic matrix and antiferromagnetic cluster containing MnA2+ ions. The phase diagram demonstrates the strong correlated interrelation among magnetic, transport and magnetoresistance properties.