New High‐ T _c Charge‐Transfer Multiferroicity in the Quasi‐2D Antiferromagnet CrSbS ₃

ABSTRACT Low‐dimensional magnets, particularly 2D systems, offer a rich platform for realizing unconventional multiferroic mechanisms, especially when multiple polarization channels coexist. In the quasi‐2D antiferromagnet CrSbS ₃ , which crystallizes in the centrosymmetric orthorhombic space group Pnma and orders magnetically at T _N ≈ 90 K, two independent polarization mechanisms are uncovered. A weak spontaneous polarization (P ₁ ) emerges near T _E ≈ T _N at zero field, driven by partial Cr charge transfer. Synchrotron XRD refinements reveal anomalies in bond valences and average Cr─S bond length, XAS detects subtle modifications in local electronic states, and Raman spectroscopy uncovers anomalous phonon softening, indicating a charge‐transfer‐driven reconstruction of the lattice and phonon. In addition, second‐harmonic generation (SHG) measurements exhibit a clear enhancement below T _E , directly confirming inversion‐symmetry breaking and supporting the emergence of the spontaneous polarization P ₁ . Further, neutron diffraction reveals a C‐type antiferromagnetic structure described by the magnetic space group Pnm'a , which breaks inversion symmetry and induces an additional polarization (P ₂ ) under applied magnetic fields. Critical exponent analysis ( β ≈ 0.23(2)) highlights quasi‐2D magnetism. These results establish CrSbS ₃ as a rare high‐ T _c / T _N (∼90 K) type‐II multiferroic, where charge, spin, lattice, and phonon degrees of freedom cooperatively produce robust ferroic responses in a 2D framework.