Exchange bias effect in martensitic epitaxial Ni-Mn-Sn thin films applied to pin CoFeB/MgO/CoFeB magnetic tunnel junctions

TL;DR

This paper demonstrates that epitaxial Ni-Mn-Sn thin films exhibit an intrinsic exchange bias effect that can be used to pin magnetic tunnel junctions, with a measurable bias field that diminishes with temperature.

Contribution

It introduces the use of Ni-Mn-Sn as an intrinsic exchange bias layer for magnetic tunnel junctions, enabling independent switching of ferromagnetic electrodes.

Findings

Exchange bias of about 130 Oe at 10 K.

Bias field decreases with temperature.

Bias vanishes above 70 K.

Abstract

The exchange bias effect is commonly used to shift the coercive field of a ferromagnet. This technique is crucial for the use of magnetic tunnel junctions as logic or memory devices. Therefore, an independent switching of the two ferromagnetic electrodes is necessary to guarantee a reliable readout. Here, we demonstrate that the intrinsic exchange bias effect of Ni-Mn-Sn can be used to apply a unidirectional anisotropy to magnetic tunnel junctions. For this, we use epitaxial Ni-Mn-Sn films as pinning layers for microfabricated CoFeB/MgO/CoFeB magnetic tunnel junctions. We compare the exchange bias field ($H_{\text{EB}}$) measured after field cooling in $-10$\,kOe external field by magnetization measurements with $H_{\text{EB}}$ obtained from tunnel magnetoresistance measurements. Consistent for both methods we find an exchange bias of about $H_{\text{EB}}=130$\,Oe at 10\,K, which decreases with increasing temperature and vanishes above 70\,K.