Ferromagnetism and Spin-Polarized Luminescence in Lead-Free CsEuCl₃ Perovskite Nanocrystals and Thin Films

The emergence of next-generation spintronic and spin-photonic technologies will be aided by the development of materials showing strongly coupled magnetic, electronic, and optical properties. Through a combination of magneto-photoluminescence and magnetic circular dichroism spectroscopies we demonstrate strong magneto-optical responses from CsEuCl₃ perovskite nanocrystals and thin films in the near-UV/visible region, stemming from the f-d transitions centered at the B-site Eu²⁺ cations. We show that this material undergoes a ferromagnetic phase transition at ∼3 K in both the nanocrystal and thin-film samples, resulting in complete spin alignment and indicating intrinsic ferromagnetism. We also report the observation of spin-polarized photoluminescence in the presence of a magnetic field at cryogenic temperatures, saturating with a large polarization ratio (ΔI/I = (I_L - I_R)/(I_L + I_R)) of nearly 30% at modest magnetic fields (∼2 T). These results highlight CsEuCl₃ as an intrinsically ferromagnetic, luminescent metal-halide perovskite with potentially interesting implications for future spin-based technologies using perovskites.