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 A(2)CuCl(4) by incorporating ortho-, meta-, and para-fluorine substitution in the benzylamine structure. Two-dimensional (2D) polar ferromagnet (3-FbaH)(2)CuCl4 (3-FbaH(+) = 3-fluorobenzylammonium) is successfully obtained, which crystallizes in a polar orthorhombic space group Pca2(1) at room temperature. In contrast, both (2-FbaH)(2)CuCl4 (2-FbaH(+) = 2-fluorobenzylammonium) and (4-FbaH)(2)CuCl4 (4-FbaH(+) = 4-fluorobenzylammonium) crystallize in centrosymmetric space groups P2(1)/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)(2)CuCl4. Preliminary magnetic measurements confirm that these three perovskites possess dominant ferromagnetic interactions within the inorganic [CuCl4](infinity) layers. Therefore, (3-FbaH)2CuCl(4) 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.

Automated summary

This study investigates the influence of positional isomerism on the crystal structure of fluorobenzylammonium copper(II) chloride perovskites. The position of the fluorine atom is found to be a key factor driving the polar behavior. By substituting different positions with fluorobenzylamine, a polar ferromagnet with potential as a type I multiferroic is successfully obtained, providing new insights for the development of high-performance 2D copper(II) halide perovskite multiferroic materials.