Impact of Fe$_{80}$B$_{20}$ insertion on the properties of dual-MgO perpendicular magnetic tunnel junctions

TL;DR

This paper investigates how inserting Fe80B20 at the interfaces of dual-MgO free layers in magnetic tunnel junctions affects their magnetic and transport properties, demonstrating a method to optimize MTJ performance for high-temperature applications.

Contribution

It introduces a novel approach to tune the properties of dual-MgO free layer MTJs using Fe80B20 insertion, enabling improved performance after high-temperature annealing.

Findings

Ultrathin Fe80B20 enhances perpendicular magnetic anisotropy and maintains low damping.

Thicker Fe80B20 layers degrade TMR and PMA, increase damping.

The method allows property tuning of MTJs up to 400°C annealing.

Abstract

We explore the impact of Fe80B20 inserted at both Co$_{20}$Fe$_{80}$B$_{20}$/MgO interfaces of dual-MgO free layers (FLs) in bottom-pinned magnetic tunnel junctions (MTJs). MTJ stacks are annealed for 30 min at 350 $^\circ$C and 400 $^\circ$C in a vacuum after film deposition. Current-in-plane tunneling measurements are carried out to characterize magnetotransport properties of the MTJs. Conventional magnetometry measurements and ferromagnetic resonance are conducted to estimate the saturation magnetization, the effective perpendicular anisotropy field and the Gilbert damping of dual-MgO FLs as a function of the Fe$_{80}$B$_{20}$ thickness and annealing temperatures. With ultrathin Fe$_{80}$B$_{20}$ (0.2 - 0.4 nm) inserted, perpendicular magnetic anisotropy (PMA) of FLs increases with similar tunnel magneto-resistance (TMR) and low damping values. As Fe$_{80}$B$_{20}$ layer thickness further increases (0.6 - 1.2 nm), both TMR and PMA degrade, and damping increases dramatically. This study demonstrates a novel approach to tune properties of MTJ stacks with dual-MgO FLs up to 400 $^\circ$C annealing, which enables MTJ stacks for various applications.