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

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.