A large unidirectional magnetoresistance in Fe–Sn heterostructure devices

Unidirectional magnetoresistance (UMR) is an attractive magnetic-field sensing technique as it enables us to detect the in-plane direction of the external magnetic field with a single element. However, the UMR amplitude is typically several orders of magnitude smaller than those of other directional magnetoresistances exhibited in ferromagnetic thin films, hindering sensing applications using the UMR. For a directional magnetic sensor using the UMR, an in-depth understanding of the mechanisms of the UMR and its enhancement are highly desirable. In this study, the structural dependence of the UMR in Fe–Sn heterostructure devices is investigated. We find a weak dependence of the UMR on interface configuration in the oxide cap/Fe–Sn heterostructures on various oxide substrates. In contrast, the normalized UMR amplitude is enhanced by a factor of 27 with increasing Fe–Sn layer thickness from 4.0 to 100 nm. These results suggest that the magnetothermal effect dominates the large UMR in the Fe–Sn heterostructure devices.