Sub‐Nanometer Thick Wafer‐Size NiO Films with Room‐Temperature Ferromagnetic Behavior

<jats:title>Abstract</jats:title><jats:p>Adding ferromagnetism into semiconductors attracts much attentions due to its potential usage of magnetic spins in novel devices, such as spin field‐effect transistors. However, it remains challenging to stabilize their ferromagnetism above room temperature. Here we introduce an atomic chemical‐solution strategy to grow wafer‐size NiO thin films with controllable thickness down to sub‐nanometer scale (0.92 nm) for the first time. Surface lattice defects break the magnetic symmetry of NiO and produce surface ferromagnetic behaviors. Our sub‐nanometric NiO thin film exhibits the highest reported room‐temperature ferromagnetic behavior with a saturation magnetization of 157 emu/cc and coercivity of 418 Oe. Attributed to wafer size, the easily‐transferred NiO thin film is further verified in a magnetoresistance device. Our work provides a sub‐nanometric platform to produce wafer‐size ferromagnetic NiO thin films as atomic layer magnetic units in future transparent magnetoelectric devices.</jats:p>