Tunneling magnetoresistance of perpendicular CoFeB-based junctions with exchange bias

TL;DR

This study investigates the tunnel magnetoresistance of perpendicular CoFeB-based magnetic tunnel junctions with exchange bias, revealing higher TMR with Hf capping due to boron absorption, and analyzes temperature-dependent coercivity behavior.

Contribution

It demonstrates that Hf capping enhances TMR in perpendicular exchange-biased junctions by absorbing boron, and provides insights into coercivity behavior modeled by Stoner-Wohlfarth including thermal effects.

Findings

Hf capping yields higher TMR (47.2%) than Ta (42.6%) at room temperature.

Higher boron absorption in Hf prevents suppression of the Δ1 channel.

Temperature-dependent coercivities follow the Stoner-Wohlfarth model with thermal fluctuations.

Abstract

Recently, magnetic tunnel junctions with perpendicular magnetized electrodes combined with exchange bias films have attracted large interest. In this paper we examine the tunnel magnetoresistance of Ta/Pd/IrMn/Co-Fe/Ta/Co-Fe-B/MgO/Co-Fe-B/capping/Pd magnetic tunnel junctions in dependence on the capping layer, i.e., Hf or Ta. In these stacks perpendicular exchange bias fields of -500\,Oe along with perpendicular magnetic anisotropy are combined. A tunnel magnetoresistance of $(47.2\pm 1.4)\%$ for the Hf-capped sample was determined compared to the Ta one $(42.6\pm 0.7)\%$ at room temperature. Interestingly, this observation is correlated to the higher boron absorption of Hf compared to Ta which prevents the suppression of $\Delta_{\textrm{1}}$ channel and leads to higher tunnel magnetoresistance values. Furthermore, the temperature dependent coercivities of the soft electrodes of both samples are mainly described by the Stoner-Wohlfarth model including thermal fluctuations. Slight deviations at low temperatures can be attributed to a torque on the soft electrode that is generated by the pinned magnetic layer system.