Quantum Bi‐Stability and Robust Room‐Temperature Spin Excitation in a Single‐Ion Magnet

The search for single‐ion magnetism (SIM) has been largely focused on hybrid metal–organic systems. Here, the spin‐relaxation mechanism of SIM is demonstrated in a pure inorganic transition‐metal oxide, , an Ising‐chain magnet, employing neutron diffraction and inelastic neutron scattering (INS), complemented by SpinW simulation and a machine‐learning framework. Interestingly, the SIM mechanism persists even in the presence of long‐range magnetic ordering, a phenomenon rarely observed. This pioneering investigation shows that bistability between the two quantum states is maintained at zero magnetic field, driven by a dominant Orbach spin‐relaxation mechanism with an effective energy barrier meV. This behavior arises from strong spin–phonon coupling in the presence of negative axial anisotropy ( meV) and the high‐spin () Co(II) ion. Furthermore, it is observed that magnon excitations persist up to room temperature, reflecting low‐dimensional magnetic interactions and extended magnetic correlations within the oxide lattice. The interplay between single‐ion magnetism and room‐temperature spin excitations underscores the tunability of magnetic anisotropy in oxide lattices. This work presents a new magnetic domain where anisotropy‐protected single‐ion memory coexists with room‐temperature magnons, allowing materials to combine information storage with collective spin transport.