The magnetism of La1.2Sr1.8Mn2O7

The critical behaviour of La1.2Sr1.8Mn2O7 has been revisited by means of st atic macroscopic magnetic properties measurements. We present a renewed ins ight on its equilibrium properties near the critical point (T-C similar to 108 K) including the determination of the fundamental characteristics of a magnetic system (anisotropy, critical exponents and crossovers in the vicin ity of the Curie temperature). It appears that two-dimensional correlations above T-C do not spread very fast, and that thus the critical fluctuations regime occurs in a moderately narrow temperature range, assessing the thre e-dimensional nature of the ferromagnetic ordering. The higher temperature contributions to the physical properties, due to stacking defects, are inte rpreted within the context of the extensive studies carried out on thin fil ms.