Does magnetization in thin-film manganates suggest the existence of magnetic clusters?

We report results of quantitative magnetization studies on epitaxial thin films of La0.60Y0.07Ca0.33MnO3-delta and La(1-x)square(x)MnO(3-delta), with square standing for vacancy on the La site. The magnetization in all samples shows significant field dependent broadening of the ferromagnetic transition. Classical mean-field analysis of magnetization data in applied fields above a few Tesla leads to a magnetic duster size of the order of a few unit cells. The density of such a magnetic cluster correlates with the doping concentration x in the compound series La(1-x)square(x)MnO(3-delta). In thin films of La0.60Y0.07Ca0.33MnO3-delta, a magnetic field dependent, non-Curie-Weiss susceptibility was found in the paramagnetic state, indicating local ferromagnetic cluster formation above macroscopic ferromagnetic ordering temperature. (C) 1996 American Institute of Physics.