Abstract:
Disordered binary magnetic alloys in a magnetic field are
investigated in the Heisenberg–Mattis model. The Green's function
is calculated for arbitrary wave vectors and energies in the case
of a weakly dilute ferromagnet. It is shown that the presence of
the magnetic field leads in this case only to the appearance of a
gap in the spectrum of the elementary excitations. The equation of
motion for the generalized coordinates of the model is used to
obtain the long-wavelength spectrum of the elementary excitations
for arbitrary concentrations of one of the components. In the case
of complete disorder, the magnetic field strongly changes the
spectrum of the elementary excitations. It is shown that for
${\mathbf k}=0$ the energy spectrum is analogous to the spectrum of a
ferromagnet.