Large and Tunable Electron-Depletion-Based Voltage-Controlled Magnetic Anisotropy in the CoFeB/MgO System via Work-Function-Engineered Pt_<i>x</i>W_1–<i>x</i> Underlayers

Abstract

Voltage-Controlled Magnetic Anisotropy (VCMA) effect is a promising strategy for reducing energy consumption in Magnetic Random-Access Memory (MRAM) for embedded applications. However, the low efficiency of VCMA poses challenges for CoFeB/MgO-based MRAM. Although significant VCMA coefficients have been predicted based on electron depletion (ED) in the orbital population model for Fe/MgO interfaces, experimental validation remains limited. Here, we demonstrate an effective and industry-compatible approach to achieving an electrical-field tunable interfacial perpendicular magnetic anisotropy (PMA) and an enhanced VCMA coefficient by synthesizing W-based metallic alloy underlayers with varying Pt concentrations, leveraging Pt's high work function and strong electronegativity. Compared with pure W control devices, the alloy with the highest Pt concentration achieves a VCMA enhancement approximately eight times greater. Additionally, significant electron depletion in the Fe 2p_3/2 and 2p_1/2 orbitals at the CoFeB/MgO interface is observed through binding energy shifts. High-resolution X-ray photoelectron spectroscopy (HR-XPS) confirms these shifts as increased binding energies, indicating reduced electron density at the interface. These findings suggest that VCMA efficiency in MRAM devices can be enhanced by controlling the Fermi surface at the CoFeB/MgO interface under thermal equilibrium.