  We report results of magnetization and ac susceptibility measurements down to
very low fields on a single crystal of the perovskite manganite,
La$_{0.82}$Ca$_{0.18}$MnO$_3$. This composition falls in the intriguing
ferromagnetic insulator region of the manganite phase diagram. In contrast to
earlier beliefs, our investigations reveal that the system is magnetically (and
in every other sense) single-phase with a ferromagnetic ordering temperature of
$\sim$ 170 K. However, this ferromagnetic state is magnetically frustrated, and
the system exhibits pronounced glassy dynamics below 90 K. Based on measured
dynamical properties, we propose that this quasi-long-ranged ferromagnetic
phase, and associated superspin glass behavior, is the true magnetic state of
the system, rather than being a macroscopic mixture of ferromagnetic and
antiferromagnetic phases as often suggested. Our results provide an
understanding of the quantum phase transition from an antiferromagnetic
insulator to a ferromagnetic metal via this ferromagnetic insulating state as a
function of $x$ in La$_{1-x}$Ca$_x$MnO$_3$, in terms of the possible formation
of magnetic polarons.
