Magneto‐Electric Directional Anisotropy in Polar Soft Ferromagnets of Two‐Dimensional Organic–Inorganic Hybrid Perovskites

Polar Ferromagnet Induced by Fluorine Positioning in Isomeric Layered Copper Halide Perovskites

We present the influence of positional isomerism on the crystal structure of fluorobenzylammonium copper(II) chloride perovskites A₂CuCl₄ by incorporating ortho-, meta-, and para-fluorine substitution in the benzylamine structure. Two-dimensional (2D) polar ferromagnet (3-FbaH)₂CuCl₄ (3-FbaH⁺ = 3-fluorobenzylammonium) is successfully obtained, which crystallizes in a polar orthorhombic space group Pca2₁ at room temperature. In contrast, both (2-FbaH)₂CuCl₄ (2-FbaH⁺ = 2-fluorobenzylammonium) and (4-FbaH)₂CuCl₄ (4-FbaH⁺ = 4-fluorobenzylammonium) crystallize in centrosymmetric space groups P2₁/c and Pnma at room temperature, respectively, displaying significant differences in crystal structures. These differences indicate that the position of the fluorine atom is a driver for the polar behavior in (3-FbaH)₂CuCl₄. Preliminary magnetic measurements confirm that these three perovskites possess dominant ferromagnetic interactions within the inorganic [CuCl₄]_∞ layers. Therefore, (3-FbaH)₂CuCl₄ is a polar ferromagnet, with potential as a type I multiferroic. This work is expected to promote further development of high-performance 2D copper(II) halide perovskite multiferroic materials.