Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures

TL;DR

This study uses first-principles calculations to uncover how different metallic capping layers influence the perpendicular magnetic anisotropy in MgO/CoFe structures, crucial for enhancing STT-MRAM performance.

Contribution

It reveals the physical mechanism behind interfacial PMA in MgO/CoFe/capping layer structures, highlighting the role of orbital hybridization and interface interactions.

Findings

PMA arises from both MgO/CoFe and CoFe/capping layer interfaces.

Variation in PMA is due to different orbital hybridizations influenced by capping materials.

Results align with experimental trends in PMA variation.

Abstract

Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbital coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM.