Electric-field effects on thickness dependent magnetic anisotropy of sputtered MgO/Co40Fe40B20/Ta structures

TLDR

The study examined CoFeB layers of 2 nm or thinner in MgO/CoFeB/Ta stacks. Applying an electric field at room temperature reverses the easy axis from in‑plane to perpendicular as CoFeB thickness falls below 2 nm, tunes perpendicular anisotropy and coercivity, and even induces superparamagnetism in layers thinner than ~0.9 nm, with the field effect persisting below the blocking temperature.

Abstract

We have investigated the effect of applied electric field EG on thickness dependent magnetic anisotropy of sputtered Co40Fe40B20 sandwiched with MgO and Ta. The range of CoFeB thickness explored is 2 nm and below. As the thickness is reduced, the easy axis of magnetization becomes perpendicular from in-plane. We show that perpendicular magnetic anisotropy of in-plane samples and coercivity of perpendicular samples can be modified by applying EG at room temperature. Furthermore, superparamagnetic behavior is observed for CoFeB layers with further reduced thickness below ≈0.9 nm, where electric-field effect is also observed below their blocking temperature.