Spin-wave softening and Hund's coupling in ferromagnetic manganites.

Using a one-orbital model of hole-doped manganites, we show with the help of the Holstein-Primakov transformation that finite Hund's coupling is responsible for the spin-wave softening in the ferromagnetic B-phase manganites. We obtain an analytical result for the spin-wave spectrum for [Formula: see text]. In the limit of infinite Hund's coupling, the spectrum is the conventional nearest-neighbour Heisenberg ferromagnetic spin-wave.