Analysis of current-in-plane giant magnetoresistance using Co2FeAl0.5Si0.5 half-metallic Heusler alloy

Current-in-plane giant magnetoresistance (CIP-GMR) devices receive revived interest for high-sensitivity magnetic sensors. However, further improvement in MR ratios is necessary to achieve sufficiently magnetic field sensitivity. The usage of half-metallic Co-based Heusler alloy ferromagnetic (FM) layer has been demonstrated to be effective in enhancing GMR in current-perpendicular-to-plane (CPP) configuration; however, only small MR ratios are obtained in the CIP configuration. To understand the origin of the disappointingly low MR in the CIP configuration using the Heusler alloy FM layers, we investigated magnetotransport properties of CIP-GMR devices using half-metallic Co2FeAl0.5Si0.5 (CFAS) Heusler alloy and conventional CoFe alloy as ferromagnetic (FM) layers in combination with Ag or Cu as nonmagnetic (NM) spacer layer. Regardless of high lattice and electronic band matching at the CFAS/Ag interface, CFAS/Ag CIP spin valves (SVs) shows the MR ratio of only 1.2% at RT, which is much smaller than those of reference CoFe/Cu and CoFe/Ag SVs, 21.6 and 8.4%, respectively. Current density distribution simulations suggest that large current shunting occurs in the Ag layer due to significant resistivity gap between CFAS and Ag, which limits the generation of highly spin-polarized current from the CFAS layer, resulting in the very small MR ratios. To enhance the MR ratio in CIP-GMR using half-metallic materials, resistivity matching between FM layers and NM layer is required in addition to the high electronic band match that has been considered as key factors to obtain high MR ratio in CIP-GMR.