Diffuse Scattering in Manganites

J. W. Lynn

NIST Center for Neutron Research

(La-Ca)MnO is a prototype system to investigate the delicate energetic balance between the magnetic, electronic, and lattice degrees of freedom. For both small and large x correlated ferromagnetic droplets form in the background of antiferromagnetic order, while in the CMR regime (x 1/3) of central interest the system is a metallic, isotropic ferromagnet in the ground state. Upon approaching the first-order metal/insulator transition, polarons form that truncate the ferromagnetic state. These short-range polarons are correlated, and an investigation of the dynamics reveals the presence of a purely elastic component in the scattering. Hence this phase has all the characteristics of a glass. Further increase of temperature results in the scattering becoming purely dynamical above the glass transition, where the polaron correlations are also lost. The overall behavior in the CMR regime of the manganites is quite similar to that observed in the relaxor ferroelectrics such as PMN, as well as the spin and charge stripes found cuprate oxides, demonstrating a commonality of many of the underlying physical concepts of these perovskite oxides. We will review the behavior of the diffuse scattering in the manganites and related systems, and discuss the application of the new thermal triple-axis instruments at the NCNR for measurements on these materials. Further information can be found at http://www.ncnr.nist.gov/staff/jeff/