Unravelling the origin of ferromagnetism and critical scaling behavior in orbital altermagnetic candidate CuBr 2 derived lead free Ruddlesden–Popper halide perovskite (PEA) 2 CuBr 4

Abstract A comprehensive understanding of the interplay between lattice structure and magnetic interactions in layered hybrid organic–inorganic metal halide perovskites is essential for guiding their rational design and functional integration into next-generation spintronic devices. Although CuCl {}₂ -based compounds exhibit superior thermal stability, the recently predicted one-dimensional orbital altermagnet CuBr {}₂ derived (PEA) {}₂ CuBr {}₄ (PECB) remains largely unexplored. A systematic investigation of PECB is carried out to elucidate its critical behavior and the nature of the ferromagnetic (FM)–paramagnetic phase transition, complemented by detailed structural and optical measurements. Different methods were employed to estimate the critical exponents near the paramagnetic to FM phase transition such as modified Arrott plots, the Kouvel–Fisher method, and the scaling hypothesis. The extracted critical exponents, β=0.263±0.021 , γ=0.854±0.007 , and δ=4.327±0.002 , were evaluated through these methods. These critical exponents are consistent with the values obtained from the scaling hypothesis and further validated by the Widom scaling relation, thereby confirming their reliability. Additionally, we examine the origin of ferromagnetism in this class of materials, emphasizing the influence of organic–inorganic coupling and lattice-mediated exchange interactions. The magnetic ground state is elucidated using DFT calculations. Our comprehensive investigation reveals that the halide perovskite PECB exhibits rich and unconventional magnetic behavior, thereby opening new pathways for the rational design and exploration of layered magnetic systems with promising prospects for spintronic applications.