Dependency of Tunneling-Magnetoresistance Ratio on Nanoscale Spacer Thickness and Material for Double MgO Based Perpendicular-Magnetic-Tunneling-Junction

Abstract

It was found that in double MgO based perpendicular magnetic tunneling junction spin-valves ex-situ annealed at 400 degrees C, the tunneling magnetoresistance ratio was extremely sensitive to the material and thickness of the nanoscale spacer: it peaked at a specific thickness (0.40 similar to 0.53 nm), and the TMR ratio for W spacers (similar to 134%) was higher than that for Ta spacers (similar to 98%). This dependency on the spacer material and thickness was associated with the (100) body-centered-cubic crystallinity of the MgO layers: the strain enhanced diffusion length in the MgO layers of W atoms (similar to 1.40 nm) was much shorter than that of Ta atoms (similar to 2.85 nm) and the shorter diffusion length led to the MgO layers having better (100) body-centered- cubic crystallinity.