Ligand Tunability of Emergent Non-collinear Magnetism in Cu-based Layered Hybrid Perovskites

Transition metal based layered organic-inorganic hybrid perovskites (OIHPs) exhibit diverse magnetic phenomena, yet the atomistic origin of magnetism in this class of materials remains elusive after decades of study. In this work, we demonstrate a striking ligand tunable magnetism in two new quasi-2D OIHPs (C₇H₉NBr)₂CuX₄ (C₇H₉NBr = 4-Bromobenzylammonium = A, X = Cl, Br) from comprehensive magnetic measurements and provide its microscopic understanding supported by ab initio DFT calculations. Despite being isostructural and having easy plane magnetocrystalline anisotropy (MCA), the Cl and Br analogs exhibit contrasting magnetic response. While A₂CuCl₄ shows an in-plane ferromagnetic and out-of-plane antiferromagnetic like response, A₂CuBr₄ follows the reverse trend. The origin of this intriguing behavior is argued to stem from the presence of Dzyaloshinskii-Moriya interaction (DMI) which is effectively quantified by employing spin spiral calculations. Based on the competition between DMI and MCA, we propose a canted and a transverse conical spiral spin structure for A₂CuCl₄ and A₂CuBr₄ respectively, which captures the observed magnetic response. Our study provides a framework to understand the occurrence of non-collinear magnetism and its ligand tunability in this class of OIHPs.