Precursor Effects of the Giant Magnetoresistance Regime in Calcium Doped Manganites

Inelastic neutron scattering has been used on La1−xCa x MnO3 compound 0with 0≤x≤0.10 to describe their dynamic magnetic properties. In addition to super exchange coupling between Mn ions (ferromagnetic (F) in (a, b) planes and antiferromagnetic (AF) along the c direction), a new type of F coupling is found, induced by mobile carriers between magnetic Mn ions. It is revealed by well-defined propagative spin wave modes with a gap and a nearly isotropic dispersion law: ω=ω0+Dq2. The q-evolution of the instantaneous spin pair correlations remind F inhomogeneities embedded in the mean AF lattice. These results could be understood in a frame of an electronic phase separation.