  A few years ago we predicted theoretically that in systems with nesting of
the Fermi surface the spin-valley half-metal has lower energy than the spin
density wave state. In this paper we suggest a possible way to distinguish
these phases experimentally. We calculate dynamical spin susceptibility tensor
for both states in the framework of the Kubo formalism. Discussed phases have
different numbers of the bands: four bands in the spin-valley half-metal and
only two bands in the spin density wave. Therefore, their susceptibilities, as
functions of frequency, have different number of peaks. Besides, the
spin-valley half-metal does not have rotational symmetry, thus, in general the
off-diagonal components of susceptibility tensor are non-zero. The spin density
wave obeys robust rotational symmetry and off-diagonal components of the
susceptibility tensor are zero. These characteristic features can be observed
in experiments with inelastic neutron scattering.
