  For broad nanoscale applications, it is crucial to implement more functional
properties, especially those ferroic orders, into two-dimensional materials.
Here GdI$_3$ is theoretically identified as a honeycomb antiferromagnet with
large $4f$ magnetic moment. The intercalation of metal atoms can dope electrons
into Gd's $5d$-orbitals, which alters its magnetic state and lead to Peierls
transition. Due to the strong electron-phonon coupling, the Peierls transition
induces prominent ferroelasticity, making it a multiferroic system. The strain
from undirectional stretching can be self-relaxed via resizing of triple
ferroelastic domains, which can protect the magnet aganist mechnical breaking
in flexible applications.
