The impact of Hf layer thickness on the perpendicular magnetic anisotropy in Hf/CoFeB/MgO/Ta films

The impact of Hf layer thickness on magnetic anisotropy is evaluated for Hf/CoFeB/MgO/Ta multilayer films commonly used in magnetic tunnel junctions (MTJs). An easy-axis magnetization transition from the in-plane to the out-of-plane direction is observed when the thickness of Hf is greater than ∼1.5 nm in our structure. Moreover, a critical Hf layer thickness exists for strong perpendicular magnetic anisotropy on the CoFeB/MgO interface that maintains the properties required for use in MTJs. We also perform X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) to study the effects of film composition, chemical states, and crystallization on the magnetic anisotropy in Hf/FeCoB/MgO/Ta multilayers with Hf layers of various thicknesses.