Giant perpendicular magnetic anisotropy in Mo/Boron-rich CoFeB/MgAl2O4 structure

Abstract

Perpendicular magnetic tunnel junctions (p-MTJs) with perpendicular magnetic anisotropy (PMA) are key devices for scaling magnetoresistance random access memories down to ∼10 nm. However, the magnetic anisotropy field Hk of the intensively studied CoFeB/MgO is still about 4–6 kOe for bottom CoFeB, and the corresponding magnetic anisotropy energy coefficient Keff is about 3 × 106–5 × 106 erg cm−3. In this study, we aim to realize a giant PMA in Mo (2 nm)/Co19Fe56B25 (tCoFeB)/MgAl2O4 (4 nm)/Ta (1 nm) stack. By using the Boron-rich Co19Fe56B25 layer in combination with the Boron-blocking Mo underlayer and the spinel MgAl2O4 oxide layer, we can realize giant PMA in CoFeB with Hk as high as 17.5–19.5 kOe and Keff as high as 6.9 × 106–9.4 × 106 erg cm−3. Auger electron spectroscopy depth profiles reveal that the good balance between the Boron-blocking Mo layer and the Boron-sink MgAl2O4 layer results in about 20% of the original Boron remaining in CoFeB, leading to a small magnetization and giant PMA. Our results pave the way for further scaling of MTJs and improved resistance against thermal and external magnetic field disturbance.