p-Orbital Ferromagnetism Arising from Unconventional O - Ionic State in a New Semiconductor Sr 2 AlO 4 with Insufficiently Bonded Oxygen.

Oxygen in solids usually exists in an O ^2- ionic state. As a result, it loses its magnetic nature of a single atom, wherein two unpaired electrons exist in its outer 2p orbitals. Here, it is shown that an unconventional stable ionic state of O ^- is realized in a new semiconductor material Sr ₂ AlO ₄ , leading to an intrinsic p-orbital ferromagnetism stable until ≈900 K. Experimental and theoretical investigations have clarified that one-fourth of the oxygen atoms in Sr ₂ AlO ₄ are insufficiently bonded in the crystal structure, resulting in a unique O ^- -state and p-orbital ferromagnetism. To date, the O ^- state is reported to exist only in non-equilibrium conditions, and p-orbital magnetism is only suggested in impurity bands with small ferromagnetic moments. The present work provides a new route for creating ferromagnetism in semiconductors and exploring new p-orbital physics and chemistry. In addition, the material shows elastic-mechanoluminescence that may enable unprecedented mechano-photonic-spintronics.
(© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)