MAGNETIC COHERENCE IN THE PARAMAGNETIC STATE OF MIXED-VALENCE MANGANITES

Small-angle neutron scattering measurements have been carried out on a ferromagnetic La0.75Sr0.25MnO3 single crystal. In the paramagnetic st ate, the observed variation of the neutron intensity above q = 0.1 Ang strom(-1) indicates the presence of nanometre size scattering objects. This in turn indicates the existence of magnetic coherence above T-c, a situation comparable to that encountered in Fe and Ni. A model invo lving a new expression for the spin correlation function has been deve loped, which gives very good fit to the data. This is however not cons istent with the presence of spin polarons in the paramagnetic state of LaSrMnO ferromagnetic manganites. (C) 1998 Elsevier Science B.V. All rights reserved.