Observation of above-room-temperature ferromagnetism in chemically stable layered semiconductor RhI₃

Two-dimensional (2D) ferromagnetic semiconductors with a room-temperature Curie temperature (T _c) are required for next-generation spintronic devices, but the current candidates suffer from a low T _c and poor chemical stability. Here, a new layered compound RhI₃ is discovered to be an above-room-temperature ferromagnetic semiconductor. This compound crystallizes in a monoclinic crystal system of space group C2/m, with the unit cell of a = 6.773(8) Å, b = 11.721(2) Å, c = 6.811(8) Å and β = 108.18(4) °. The structure consists of honeycomb rhodium layers separated by iodine–iodine van der Waals gap. Chemically stable RhI₃ possesses an optical bandgap of 1.17 eV. Its robust ferromagnetism with a T _c of above 400 K, which is far higher than 61 K for the well-known CrI₃ and the highest among the bulk 2D ferromagnetic semiconductors. The robust intrinsic ferromagnetic response is attributed to the Rh²⁺ and exchange interactions between I-p and Rh-d electrons induced by iodine vacancies. This work reveals that RhI₃ is a prime candidate for spintronic devices above room temperature and provides a strategy to obtain high temperature 2D ferromagnetic semiconductors by introducing vacancies. (paper)