Unconventional spin-dynamics in a phase separate, weakly disordered perovskite manganite*

The intense investigation of perovskite manganites has revealed a variety of fascinating properties. The phenomena known as phase separation, the coexistence at different length scales of ferromagnetic, charge/orbital order has been recently recognized as an intrinsic feature of several strongly correlated electron systems. Using inelastic neutron scattering, we have studied the spin dynamics of the archetypical material (La,Pr)$_{7/8}$Ca$_{3/8}$MnO$_{3}$, where competing ground states coexist at low temperature. The low-$T$ spin wave excitations at H = 0 and 2T are drastically different. We discuss this difference in terms of magnetic excitations from ferromagnetic clusters of different length scales.