High Throughput Discovery of 2D Ferromagnetic and Multiferroic Transition Metal Oxyhalides and Nitrogen Halides

Two-dimensional (2D) transition metal oxyhalides and nitrogen-halides (TMBXs, where TM = transition metal, B = O-group and N-group elements, X = halogen) have emerged as promising candidates for exploring multiferroic orders and spintronic applications. In this study, we conduct a systematic first-principles high-throughput screening combined with machine learning to identify novel 2D ferromagnetic and multiferroic materials within TMBX family. From a comprehensive dataset comprising 672 TMBX monolayers, we identify 78 ferromagnetic systems, of which 38 exhibit high Curie temperatures (TC ≥ 200 K), significantly expanding the known library of 2D magnetic materials. A machine learning model is developed to elucidate the key factors governing ferromagnetism, revealing that the second-nearest neighbor exchange interaction (J2) plays a dominant role in determining TC. Furthermore, we discover seven ferromagnetic-ferroelectric multiferroic systems, revealing unique polarization switching pathways. Notably, spin transport simulations using the nonequilibrium Green's function formalism demonstrate exceptional spin filtering capabilities (~ 100 %) and giant bias-dependent tunneling magnetoresistance (> 105 %). These findings deepen the fundamental understanding of 2D multiferroics and establish a solid platform for future experimental exploration and the development of next-generation spintronic devices.