MAGNETIC COHERENCE ABOVE THE CURIE-POINT IN FERROMAGNETIC LASRMNO MANGANITES

Small-Angle polarised Neutron Scattering (SANS) measurements have been carried out on a ferromagnetic La0.75Sr0.25MnO3 single crystal. In th e vicinity of the Curie point a substantial neutron intensity above q = 0.05 Angstrom(-1) appears which indicates the presence of nanometre size inhomogeneities mainly of magnetic origin. The neutron spectra ca nnot be explained with a picture of spin clusters moving in a paramagn etic background, i.e. magnetic polarons. Rather, a model describing an average magnetic coherence extending over several Mn spins leads to v ery good fits to the data. This situation is comparable to that encoun tered in Fe or Ni close to T-c but not completely similar. Indeed, mag netic coherence above T-c is significantly stronger in the manganites where an unusual spin correlation function had to be used to fit the d ata.