Electric field-tunable ferromagnetism in a van der Waals semiconductor up to room temperature

Ferromagnetic semiconductors, coupling charge transport and magnetism via electrical means, show great promise for spin-based logic devices. Despite decades of efforts to achieve such co-functionality, maintaining ferromagnetic order at room temperature remains elusive. Here, we address this long-standing challenge by implanting dilute Co atoms into few-layer black phosphorus through atomically-thin boron nitride diffusion barrier. Our Co-doped black phosphorus-based devices exhibit ferromagnetism up to room temperature while preserving its high mobility (~ ${1000\mathrm{cm}}^2{V}^{-1}{s}^{-1}$ ) and semiconducting characteristics. By incorporating ferromagnetic Co-doped black phosphorus into magnetic tunnel junction devices, we demonstrate a large tunnelling magnetoresistance that extends up to room temperature. This study presents a new approach to engineering ferromagnetic ordering in otherwise nonmagnetic materials, thereby expanding the repertoire and applications of magnetic semiconductors envisioned thus far.