The study of origin of interfacial perpendicular magnetic anisotropy in ultra-thin CoFeB layer on the top of MgO based magnetic tunnel junction

Abstract

A comprehensive microstructure study has been conducted experimentally for identifying the origin or mechanism of perpendicular magnetic anisotropy (PMA) in the ultra-thin (10 Å) CoFeB layer on the top of magnetic tunnel junction (MTJ). The high resolution transmission electron microscopy reveals that the feature of crystal structure in 10 Å-CoFeB layer is localized in nature at the CoFeB-MgO interface. On the other hand, the strain-relaxed crystalline structure is observed in the thick CoFeB (20 Å) layer at the CoFeB-MgO interface, associated with a series of dislocation formations. The electron energy loss spectroscopy further suggests that the local chemical stoichiometry of the ultra-thin 10 Å-CoFeB layer is notably changed at the CoFeB-MgO interface, compared with an atomic stoichiometry in a thick 20 Å-CoFeB layer. The origin of PMA mechanism is therefore identified experimentally as an interface effect, which can be attributed to a change of local atom bonding or lattice constant of the transition metal at the CoFeB-MgO based MTJ interface. Furthermore, such a local interfacial atom bonding change is seemly induced by the localized anisotropic strain and consistent with previous theoretical speculations and calculations. The observed experimental findings provide some perspective on microstructure and chemistry on PMA in ultra-thin CoFeB film at the MTJ interface, then deepening our understanding of the mechanism of PMA within MTJ stack and thus facilitating advancement for emerging spintronics technology.

Control of crystallization and magnetic properties of CoFeB by boron concentration

“…The cross-sectional TEM images and FFT patterns for the middle of layer of CoFeB (Fig. 1 a–g, inset 2) show the shape of textured poly-crystal/defined FFT spots up to 5% respectively, and untextured structure/ring shaped FFT pattern from 6% of boron 7 . In addition, in the XRD result shown in Fig.…”

CoFeB/MgO/CoFeB structures with orthogonal easy axes: perpendicular anisotropy and damping

“…At present, there is no doubt that PMA in MgO/CoFeB structures is an interface effect and it is correlated with the presence of oxygen atoms at the interface despite the weak spin-orbit coupling [20,25]. The origin of PMA is attributed to hybridization of the O-p with Co(Fe)-d orbitals at the interface [20] and/or to a significant contribution of thickness dependent magnetoelastic coupling [15].…”

Interfacial Transport Study of Ultra-Thin InN-Enhanced Quantum Dot Solar Cells

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