Fully compensated ferrimagnetism with high magnetic transition temperature in stable two-dimensional unconventional stoichiometric CrI crystal

Two-dimensional (2D) fully compensated collinear magnetic materials offer significant advantages for spintronic applications, including robustness against magnetic field perturbations, no stray fields, and ultrafast dynamics. Among these materials, fully compensated ferrimagnets are particularly promising due to their unique characteristics such as magneto-optical effect, completely spin-polarized currents, and anomalous Hall effect. Here, we performed a structural search on 2D unconventional stoichiometric CrI crystals using a global optimization algorithm. The most stable CrI-P21/m monolayer is a fully compensated ferrimagnetic semiconductor with a band gap of 1.57 eV and a high magnetic transition temperature of 592 K. The spontaneous spin splitting in CrI-P21/m originates from the inequivalent local coordination environments of Cr¹ and Cr² ions, yielding a mismatch in their 3d orbitals splitting. Notably, carrier doping at a concentration of 0.01 electrons or holes per atom enables reversible spin polarization, generating a fully spin-polarized current in CrI-P21/m. This performance makes it a highly promising candidate for spintronic devices. Our findings not only provide a structural paradigm for discovering fully compensated ferrimagnets but also open a new avenue for designing zero-moment magnetic materials with intrinsic spin splitting.