Tunneling magnetoresistance in magnetic tunnel junctions with a single ferromagnetic electrode

Abstract

Magnetic tunnel junctions (MTJs) are key components of spintronic devices, such as magnetic random-access memories. Normally, MTJs consist of two ferromagnetic (FM) electrodes separated by an insulating barrier layer. Their key functional property is tunneling magnetoresistance (TMR), which is a change in MTJ's resistance when magnetization of the two electrodes alters from parallel to antiparallel. Here, we demonstrate that TMR can occur in MTJs with a single FM electrode, provided that the counterelectrode is an antiferromagnetic (AFM) metal that supports a spin-split band structure and/or a N\'eel spin current. Using $\mathrm{Ru}{\mathrm{O}}_{2}$ as a representative example of such antiferromagnet and $\mathrm{Cr}{\mathrm{O}}_{2}$ as a FM metal, we design all-rutile $\mathrm{Ru}{\mathrm{O}}_{2}/\mathrm{Ti}{\mathrm{O}}_{2}/\mathrm{Cr}{\mathrm{O}}_{2}$ MTJs to reveal a nonvanishing TMR. Our first-principles calculations predict that magnetization reversal in $\mathrm{Cr}{\mathrm{O}}_{2}$ significantly changes conductance of the MTJs stacked in the (110) or (001) planes. The predicted giant TMR effect of about 1000% in the (110)-oriented MTJs stems from spin-dependent conduction channels in $\mathrm{Cr}{\mathrm{O}}_{2}$ (110) and $\mathrm{Ru}{\mathrm{O}}_{2}$ (110), whose matching alters with $\mathrm{Cr}{\mathrm{O}}_{2}$ magnetization orientation, while TMR in the (001)-oriented MTJs originates from the N\'eel spin currents and different effective $\mathrm{Ti}{\mathrm{O}}_{2}$ barrier thickness for two magnetic sublattices that can be engineered by the alternating deposition of $\mathrm{Ti}{\mathrm{O}}_{2}$ and $\mathrm{Cr}{\mathrm{O}}_{2}$ monolayers. Our results demonstrate a possibility of a sizable TMR in MTJs with a single FM electrode and offer a practical test for using the antiferromagnet $\mathrm{Ru}{\mathrm{O}}_{2}$ in functional spintronic devices.