Diffuse magnetic scattering above TC in quasi-two-dimensional La1.2Sr1.8Mn2O7 -: art. no. 134440

The exchange interaction introduced independently by Heisenberg and Dirac in 1926 is key to understanding magnetic properties of materials, including technologically relevant colossal magnetoresistive (CMR) manganites. Here we show that the diffuse magnetic scattering above the magnetic transition temperature can yield exchange parameters. We have measured the magnetic diffuse scattering from the quasi-two-dimensional bilayer manganite La1.2Sr1.8Mn2O7 which shows CMR behavior close to the ordering temperature T-C. By fitting the experimentally measured intensity distribution of the diffuse scattering in the (h0l) plane to model mean-field calculations, we have been able to determine the nearest-neighbor exchange interaction between the Mn ions in the a-b plane and also that between the two planes of the bilayer.