Enabling high giant magnetoresistance in ultrathin-free-layer spin valves

Abstract

Emerging spin-orbit-torque devices based on spin valves require an ultrathin (e.g., $\lesssim$2 nm) magnetic free layer to maximize the torque per moment. However, reducing the free-layer thickness deteriorates the giant magnetoresistance (GMR) signal for electrical readout. Here, we demonstrate that the addition of a 1-nm Cu seed layer enables high GMR ratios of 5-7% at free-layer thicknesses of $\lesssim$2 nm by promoting high-quality, textured growth of spin valves. Our work offers a pathway for engineering high-signal GMR readout in spin-orbit-torque digital memories and neuromorphic computers.

Figures (4)

• Figure 1: (a) XRR data (symbols) and fits (solid curves) for Ti- and Ti/Cu-seeded Co(30 nm) films. The fits were used to extract the interfacial width $\sigma$ (diffuseness or roughness). (b) XRD of Ti- and Ti/Cu-seeded Co(3.0 nm)/Cu(3.5 nm)/Co(3.0 nm) stacks.
• Figure 2: Sheet conductance for Ti/SV and Ti/Cu/SV plotted against the Co free-layer thickness.
• Figure 3: (a,b) Representative GMR curves from the Ti/SV and Ti/Cu/SV series with free-layer thicknesses of (a) $5.5$ nm and (b) $1.5$ nm. (c) GMR ratio as a function of Co free-layer thickness for Ti/SV and Ti/Cu/SV.
• Figure 4: GMR ratio as a function of Cu seed-layer thickness with a Co free-layer thickness of 5 nm.