Spin correlations and magnetoresistance in the bilayer manganite La1.2Sr1.8Mn2O7

We have studied the magnetic correlations in the x = 40% hole doped bilayer manganite La1.2Sr1.8Mn2O7 using neutron scattering. The in-plane correlations obey standard two-dimensional scaling above T-C similar to 113 K with a crossover towards three-dimensional critical behavior close to T-C, consistent with quasi two-dimensional critical fluctuations. This suggests that conventional magnetism drives the phase transition while simultaneously destroying the charge correlations observed in the paramagnetic region. (C) 2002 Elsevier Science B.V. All rights reserved.