  An anomaly in the magnon dispersion of the amorphous ferromagnet Co$_{4}$P,
often referred to as a `roton-like' excitation, attracted much attention half a
century ago. With the current interest in heat and spin currents in amorphous
magnets, we apply modern simulation methods, combining reverse Monte Carlo to
build the atomic structure and the stochastic Landau-Lifshitz equation for spin
dynamics, to re-investigate the magnetic excitation spectrum. We find two
magnon valleys, one at the origin and another at a finite wavenumber close to
the observations, but without a magnon gap. We conclude that the second dip is
due to Umklapp scattering caused by residual long-range order, which may be an
alternative explanation of the putative roton excitation. Our study paves the
way to study magnon transport in amorphous magnets and related spintronic
applications.
