Electric‐Field‐Controlled Interconversion of Antiferromagnetic States in a Two‐Dimensional Antiferroelectric Halide Perovskite

ABSTRACT Electric‐field control of spin‐dependent electronic structures in antiferromagnets is highly desirable for low‐power spintronic devices, however, such control remains largely unexplored. Here, we propose a promising route based on electric‐field‐driven switching between symmetry‐distinct altermagnetic (AM) and type‐IV antiferromagnetic (AFM) states, enabling reversible interconversion between spin‐split and spin‐degenerate electronic structures. First‐principles calculations identify the organic‐inorganic halide perovskite multiferroic monolayer as a candidate platform for realizing this concept. This monolayer possesses two inequivalent antiferroelectric (AFE) structures that host distinct AFM electronic states: one realizes an AM state with nonrelativistic spin splitting, whereas the other belongs to the type‐IV AFM class with spin‐degenerate bands in the nonrelativistic limit. Remarkably, an in‐plane electric field as low as 0.017 V/Å drives a transition between the two AFE phases, thereby switching the system between an AM spin‐split state and a spin‐degenerate type‐IV AFM state. Moreover, the two AFM states exhibit distinct, symmetry‐governed Kerr rotation responses, enabling optical detection of the electric‐field‐driven interconversion. These findings establish AFE interconversion as a ferroic‐order‐based route for electrically programming symmetry‐distinct AFM electronic states, providing a new route for low‐power, optically readable AFM spintronics.