Spin-wave spectrum of an amorphous ferromagnet

The spin-wave spectrum of an amorphous Heisenberg ferromagnet is calculated by a diagrammatic expansion making use of a transformation suggested by Taylor and Wu. The upper limit of the spectrum is found to occur at frequencies below those of the corresponding crystalline system, while the low-frequency part of the spectrum is enhanced. Internal van Hove singularities are absent in the spin-wave spectrum of the amorphous ferromagnet.