Magnetic correlations in the bilayer manganite La1.2Sr1.8Mn2O7

Neutron scattering has been used to study the magnetic correlations in the double-layer manganite La1.2Sr1.8Mn2O7, which exhibits colossal magnetoresi stance in the vicinity of the ferromagnetic transition at T-c = 112 K. Over a large temperature range above T-c, there is evidence for two-dimensional magnetic correlations which peak in intensity at the transition. Although the in-plane correlations are predominantly ferromagnetic, a strong canting of spins in neighboring planes within the bilayers, at an angle that is de pendent on both the temperature and magnetic field, is observed. There are indications of a crossover to three-dimensional critical scattering very cl ose to T-c, but the nature of the phase transition has yet to be determined . (C) 1998 American Institute of Physics.