Magnetic and Dielectric Properties of CoFeB Multilayer Thin Films With Oxide Capping Layer

Ferromagnetic multilayer thin films with oxide capping layer have potential applications in voltage-controlled magnetic devices. Here, we present the optimization of the magnetic and dielectric properties of CoFeB/MgO thin films with different capping layers (Ta, Al
₂
O
₃
, and HfO
₂
). We find that the samples with oxide capping layers show a higher perpendicular magnetic anisotropy (PMA) than those with a Ta capping layer. Meanwhile, a high dielectric constant of 58 is obtained in samples capped with 30 nm of HfO
₂
. This high dielectric constant is attributed to the formation of an oxygen vacancy-related capacitive double layer in the HfO
₂
film according to X-ray diffraction analyses and current–voltage measurements. Finally, we find that the optimal annealing temperature, which allows for both high PMA and dielectric constant, is between 250 °C and 290 °C. Our results could contribute to designing high-performance materials for controlling interfacial magnetic properties in novel spintronic devices.