Abstract
Ca- and Sr-doped lanthanum manganese perovskites La0.95A0.05Mn0.98Fe0.02O3+δ (A = Ca, Sr) (LCM and LSM) of non-stoichiometric (NS) and stoichiometric (S) compositions were prepared by sol-gel method and investigated by 57Fe Mössbauer spectroscopy and magnetic measurements. In contrast to non-stoichiometric samples, which contain pure singles phases, a mixture of orthorhombic phases O (PnmaI), O′ (PnmaII)and O′′ (PnmaII*)are detected in samples of stoichiometric compositions. The magnetic data, supported by Mössbauer measurements, show the spontaneous formation of magnetically ordered clusters with sizes in the range 2.5–4.6 nm in all samples. The main differences between the investigated LCM and LSM systems, and in particular the less extended phase separation in LSM-S than in LCM-S is connected to the difference in ionic radii on the doping ions, the influence of the Jahn-Teller effect at the Mn+3 centres and the size distributions of the ferromagnetic clusters. Our results show, for the first time, that the O′′ (PnmaII*) phase is characterized by antiferromagnetic ordering.