  The two-dimensional Wigner crystal (WC) occurs in the strongly interacting
regime ($r_s \gg 1$) of the two-dimensional electron gas (2DEG). The magnetism
of a pure WC is determined by tunneling processes that induce multi-spin
ring-exchange interactions, resulting in fully polarized ferromagnetism for
large enough $r_s$. Recently, Hossain et al. [PNAS 117 (51) 32244-32250]
reported the occurrence of a fully polarized ferromagnetic insulator at $r_s
\gtrsim 35$ in an AlAs quantum well, but at temperatures orders of magnitude
larger than the predicted exchange energies for the pure WC. Here, we analyze
the large $r_s$ dynamics of an interstitial defect in the WC, and show that it
produces local ferromagnetism with much higher energy scales. Three hopping
processes are dominant, which favor a large, fully polarized ferromagnetic
polaron. Based on the above results, we speculate concerning the phenomenology
of the magnetism near the metal-insulator transition of the 2DEG.
