Enhanced current-perpendicular-to-plane giant magnetoresistance effect in half-metallic NiMnSb based nanojunctions with multiple Ag spacers

Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) heterostructure devices using half-metallic NiMnSb Heusler alloy electrodes with single, dual, and triple Ag spacers were fabricated. The NiMnSb alloy films and Ag spacers show (001) epitaxial growth in all CPP-GMR multilayer structures. The dual-spacer CPP-GMR nanojunction exhibited an enhanced CPP-GMR ratio of 11% (a change in the resistance-area product, ΔRA, of 3.9 mΩ μm²) at room temperature, which is approximately twice (thrice) of 6% (1.3 mΩ μm²) in the single-spacer device. The enhancement of the CPP-GMR effects in the dual-spacer devices could be attributed to improved interfacial spin asymmetry. Moreover, it was observed that the CPP-GMR ratios increased monotonically as the temperatures decreased. At 4.2 K, a CPP-GMR ratio of 41% (ΔRA = 10.5 mΩ μm²) was achieved in the dual-spacer CPP-GMR device. This work indicates that multispacer structures provide an efficient enhancement of CPP-GMR effects in half-metallic material-based CPP-GMR systems.