  In this work we study the propagations of normal frequency modes for quantum
hydrodynamic (QHD) waves in the linear limit and introduce a new kind of
instability in a double-degenerate plasma. Three different regimes, namely,
low, intermediate and high magnetic field strengths are considered which span
the applicability of the work to a wide variety of environments. Distinct
behavior is observed for different regimes, for instance, in the
laboratory-scale field regime no frequency-mode instability occurs unlike those
of intermediate and high magnetic-field strength regimes. It is also found that
the instability of this kind is due to the heavy-fermions which appear below a
critical effective-mass parameter ($\mu_{cr}=\sqrt{3}$) and that the responses
of the two (lower and upper frequency) modes to fractional effective-mass
change in different effective-mass parameter ranges (below and above the
critical value) are quite opposite to each other. It is shown that, the
heavy-fermion instability due to extremely high magnetic field such as that
encountered for a neutron-star crust can lead to confinement of stable
propagations in both lower and upper frequency modes to the magnetic poles.
Current study can have important implications for linear wave dynamics in both
laboratory and astrophysical environments possessing high magnetic fields.
