  We investigate the propagation characteristics of electrostatic waves in a
magnetized pair-ion plasma with immobile charged dusts. It is shown that
obliquely propagating (OP) low-frequency (in comparison with the negative-ion
cyclotron frequency) long-wavelength "slow" and "fast" modes can propagate,
respectively, as dust ion-acoustic (DIA) and dust ion-cyclotron (DIC)-like
waves. The properties of these modes are studied with the effects of
obliqueness of propagation $(\theta)$, the static magnetic field, the ratios of
the negative to positive ion masses $(m)$ and temperatures $(T)$ as well as the
dust to negative-ion number density ratio $(\delta)$. Using the standard
reductive perturbation technique, we derive a Korteweg-de Vries (KdV) equation
which governs the evolution of small-amplitude OP DIA waves. It is found that
the KdV equation admits only rarefactive solitons in plasmas with $m$ well
below its critical value $m_c~(\gg1)$ which typically depends on $T$ and
$\delta$. It is shown that the nonlinear coefficient of the KdV equation
vanishes at $m=m_c$, i.e., for plasmas with much heavier negative ions, and the
evolution of the DIA waves is then described by a modified KdV (mKdV) equation.
The latter is shown to have only compressive soliton solution. The properties
of both the KdV and mKdV solitons are studied with the system parameters as
above, and possible applications of our results to laboratory and space plasmas
are briefly discussed.
