Evidence for the Griffiths phase in pure and Y-, Ca- and Cr-doped LaSr2Mn2O7 manganites

The paramagnetic susceptibility measured on La1−xYxSr2−yCay Mn2O7 (x, y or z=0, 0.03 and 0.1) manganites does not obey the Curie-Weiss law. The Curie constant exceeds the expected values by more than order of magnitude. Based on strong disorder we have compared the experimental data with predictions based on Griffith's singularity model. We find that this model allows for consistent interpretation of the data in contrary to a model assumes that magnetic polarons make contribution akin to cluster to susceptibility. In particular the values of Curie constant agree excellently with those theoretically expected, whereas the magnetic polarons model is less satisfactory.