2-DIMENSIONAL INTRINSIC AND EXTRINSIC FERROMAGNETIC BEHAVIOR OF LAYERED LA1.2SR1.8MN2O7 SINGLE-CRYSTALS

The low-field magnetization M and susceptibility chi are reported for the two-layered Ruddleson-Popper phase SrO(La1-xSrxMnO3)(2) for x=0.4 (denoted La1.2Sr1.8Mn2O7) with an in-plane magnetic easy axis. As T ap proaches the Curie temperature (T-C=116 K) on cooling, where the metal -insulator transition occurs in zero field, chi diverges as H-1/delta' , with delta=21+/-5. Also, near an extrinsic Curie transition attribut ed to similar to 0.1% fraction of intergrowths at T=2.47 T-C, M scale s as (1-T/T)(beta), with beta=0.25+/-0.02. These results can be unders tood within the context of two-dimensional XY models, and provide some perspective of the layered manganites.