Low Gilbert Damping in Perpendicularly Magnetized W/CoFeB/MgO Films with High Thermal Sustainability*

To advance the field of spintronics, it is imperative to study worthwhile materials to improve performance. For technologies such as magnetoresistive random access memory (MRAM), the recent focus has been on materials with perpendicular magnetic anisotropy (PMA) due to their reduced critical switching current and higher memory density. Interfacial PMA structures such as NM/CoFeB/MgO (where NM is a nonmagnetic metal) have been shown to be an effective structure. One of the most common interfacial PMA structures uses Ta, but annealing at temperatures exceeding 350 °C causes the Ta/CoFeB/MgO structures to breakdown. In this work, we developed and demonstrated a PMA structure of W/CoFeB/MgO that can sustain annealing temperatures up to 400 °C. The magnetization dynamics were captured with a time-resolved magneto-optical Kerr effect (TR-MOKE) technique. It was found that the Gilbert damping in W/CoFeB/MgO samples reached a minimum at an annealing temperature of 350 °C. Additionally, the damping of the W/CoFeB/MgO structure annealed at 400 °C increased to only ~0.02. This suggests that W/CoFeB/MgO, with enhanced thermal stability, are viable alternatives to Ta/CoFeB/MgO for spintronic devices.