Possible gapless spin-liquid state in the Fe-based halide perovskite Cs4BiFeBr10 derived from the antiferromagnet CsFeBr4†

Recently, magnetic halide perovskites have gained considerable attention due to their potential applications in spintronics. Iron-based halide perovskites are a type of intrinsic magnetic material with robust long-range antiferromagnetic (AFM) ordering, which is a potential parent compound for achieving the spin-liquid state. Herein, we reported the magnetic properties of S = 5/2 spin systems CsFeBr₄ and Cs₄BiFeBr₁₀, both of which possess similar nonbonding Fe–Fe zigzag chains along the b direction. By contrast, compared to CsFeBr₄, the insertion of [BiBr₆] octahedra between Fe–Fe zigzag chains induced changes in the distance and angles of neighbor [FeBr₄] tetrahedra in Cs₄BiFeBr₁₀. Magnetic and specific heat measurements showed the presence of robust long-range AFM ordering in CsFeBr₄ single crystals, while no anomalies indicative of long-range magnetic ordering were found in Cs₄BiFeBr₁₀ single crystals. Competition between two main magnetic exchange pathways, J₁ and J₂, induced magnetic frustration in Cs₄BiFeBr₁₀ with the possible gapless spin-liquid state under low temperatures.