Structural and magnetic disorder in La1-xSrxMnO3

Total structure Factors, that is both Bragg and diffuse scattering, have be en measured for La1-xSrxMnO3 (x = 0.2 and 0.4) at temperatures between 15 a nd 1000 K by powder neutron diffraction using the SLAD diffractometer at th e Studsvik Neutron Research Laboratory. The data have been used to simultan eously model the atomic and magnetic structures using the reverse Monte Car lo (RMC) method. The RMC models confirm that there are local lattice distor tions, involving the O octahedra surrounding Mn ions, that disappear as T d ecreases through T-c (here defined as the point of inflexion of the net mag netic moment determined from Rietveld refinement, representing the onset of long range ferromagnetic order). The distortion referred to is away from t he 'normal' Jahn-Teller distorted octahedron associated with Mn3+ and towar ds the more uniform octahedron associated with Mn4+. It involves more than a single octahedron, so the correlation length is larger than similar to 5 Angstrom. The models are consistent with the proposal that the distortions occur around Mn4+ ions, though it is not possible to say whether the extra charge is localized on a single Mn. They may therefore be considered as lat tice polarons. Both long range magnetic order (LRMO) and short range magnet ic order (SRMO) increase rapidly as T decreases through T-c, but SRMO also persists above T-c. This is evidence for the existence of magnetic polarons above T-c. For the first time we show that the SRMO is correlated with the Local lattice distortion, a higher ferromagnetic correlation bring associa ted with shorter Mn-Mn distances. Lattice and magnetic polarons are therefo re one and the same.