  Understanding the stability limitations and defect formation mechanisms in 2D
magnets is essential for their utilization in spintronic and memory
technologies. Here, we correlate defects in mono- to multilayer CrSBr with
their structural, vibrational and magnetic properties. We use resonant Raman
scattering to reveal distinct vibrational defect signatures. In pristine CrSBr,
we show that bromine atoms mediate vibrational interlayer coupling, allowing
for distinguishing between surface and bulk defect modes. We show that
environmental exposure causes drastic degradation in monolayers, with the
formation of intralayer defects. Through deliberate ion irradiation, we tune
the formation of defect modes, which we show are strongly polarized and
resonantly enhanced, reflecting the quasi-1D electronic character of CrSBr.
Strikingly, we observe pronounced signatures of spin-phonon coupling of the
intrinsic phonon modes and the ion beam induced defect modes throughout the
magnetic transition temperature. Overall, we demonstrate that CrSBr shows air
stability above the monolayer threshold, and provide further insight into the
quasi-1D physics present. Moreover, we demonstrate defect engineering of
magnetic properties and show that resonant Raman spectroscopy can serve as a
direct fingerprint of magnetic phases and defects in CrSBr.
