Visualizing Magnetostructural Order in Rare‐Metastable Polymorph ε‐Fe ₂ O ₃ Through Domain‐Resolved Raman Spectroscopy

Understanding and controlling magnetic domains is central to advancing spintronic and magnetoelectric technologies. However, direct, noninvasive imaging of these domains in complex oxides remains elusive, limited by the complexity, invasiveness, or environmental constraints of established techniques. Here, we demonstrate that Raman‐active phonons can serve as optical fingerprints of magnetostructural domains in the rare‐metastable polymorph ε‐Fe 2 O 3 , a high‐anisotropy ferrimagnet synthesized as hexagonal flakes via chemical vapor deposition. Mapping a symmetry‐sensitive phonon using micro‐Raman spectroscopy reveals a striking sixfold domain pattern arising from 60° crystallographic twins, showing a close spatial correspondence between lattice orientation and magnetic‐domain behavior. Temperature‐dependent Raman mapping shows that the domain contrast weakens near the Curie‐temperature range, concomitant with the collapse of magnetic coercivity, while field‐dependent longitudinal magneto‐optic Kerr‐effect imaging reveals reversible magnetic‐domain reconfiguration under applied magnetic fields. Raman‐identified domains were further confirmed by independent structural and magnetic probes. Overall, Raman spectroscopy provides a nondestructive optical probe of magnetostructural‐domain fingerprints across a wide thermal range, offering a route to correlate lattice symmetry with magnetic behavior in metastable ferrimagnets.