Tunneling magnetoresistance in magnetic tunnel junctions with a single ferromagnetic electrode (2310.02139v1)

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) that 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 counter electrode is an antiferromagnetic (AFM) metal that supports a spin-split band structure and/or a N\'eel spin current. Using RuO${2}$ as a representative example of such antiferromagnet and CrO${2}$ as a FM metal, we design all-rutile RuO${2}$/TiO${2}$/CrO${2}$ MTJs to reveal a non-vanishing TMR. Our first-principles calculations predict that magnetization reversal in CrO${2}$ 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 CrO${2}$ (110) and RuO${2}$ (110), whose matching alters with CrO${2}$ magnetization orientation, while TMR in the (001) oriented MTJs originates from the N\'eel spin currents and different effective TiO${2}$ barrier thickness for the two magnetic sublattices that can be engineered by the alternating deposition of TiO${2}$ and CrO${2}$ 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 altermagnet RuO$_{2}$ in functional spintronic devices.