Composition-Driven Control of Magnetic Anisotropy in Hybrid Organic-Inorganic Metal Halides.

Two-dimensional (2D) magnetic materials provide a fertile platform for exploring low-dimensional magnetism and anisotropy-driven magnetic ordering, yet achieving continuous and controllable tuning of magnetic anisotropy remains a significant challenge. Here, we report a systematic chemical strategy to modulate magnetic anisotropy in a family of quasi-2D-layered hybrid organic-inorganic perovskites, (PEA)2Mn1-xCuxCl4 (0 ≤ x ≤ 1). Single crystals spanning the full compositional range were grown via a slow evaporation method, yielding phase-pure materials that exhibit continuous solid-solution behavior without phase segregation. Structural characterization confirms a common layered framework across all compositions, with gradual lattice evolution upon Mn2+/Cu2+ substitution. Comprehensive DC and AC magnetization measurements performed along orthogonal crystallographic directions reveal a progressive transformation of the magnetic ground state from Ising-type antiferromagnetism in (PEA)2MnCl4 to XY-type ferromagnetism in (PEA)2CuCl4. Intermediate compositions display coexistence of antiferromagnetic and ferromagnetic interactions, accompanied by a continuous crossover from easy-axis to easy-plane magnetic anisotropy. Field-dependent measurements further demonstrate a coherent evolution of spin-flop behavior, hysteresis, and saturation magnetization across the series. These results establish chemical substitution as an effective and versatile route for engineering magnetic anisotropy in hybrid perovskites, positioning transition-metal-based 2D HOIPs as a chemically programmable platform for tunable low-dimensional magnetism and future spintronic applications.