A few perovskite-like and fluorite-like samples in which M=Pr, Sm or Tb substitutes for La have been characterised by electron magnetic resonance (EMR) spectroscopy and other techniques. Ferromagnetic (FM) systems form with the fresh biphasic sample with M =Sm only, but not after recalcination, when it becomes monophasic. These systems could be formed of Magnetic Bound Polarons due to the thermally excited J=1 Sm2+ ions present as impurity in the former case. FM systems form also with the M = Tb sample, but only after catalytic use. In this case FM systems could be composed of Tb4+ ions forming during sample re-oxidation. All these EMR observations have been correlated with the catalytic performance of these samples. (c) 2005 Elsevier B.V. All rights reserved.