Suppression of the Magnetic Phase Transition in Manganites Close to the Metal-Insulator Crossover

We report the suppression of the magnetic phase transition in La1-xCaxMnO3 close to the localized-to-itinerant electronic transition, i.e. at x = 0.2 and x = 0.5. A new crossover temperature Tf can be defined for these compositions instead of TC. Unlike in common continuous magnetic phase transition the susceptibility does not diverge at Tf and a spontaneous magnetization cannot be defined below it. We propose that the proximity to the doping-induced metal-insulator transition introduces a random field which breaks up the electronic/magnetic homogeneity of the system and explains these effects.