Tunneling magnetoresistance in magnetic tunnel junctions with a single ferromagnetic electrode

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 RuO₂ as a representative example of such antiferromagnet and CrO₂ as a FM metal, we design all-rutile RuO₂/TiO₂/CrO₂ MTJs to reveal a nonvanishing TMR. Our first-principles calculations predict that magnetization reversal in CrO₂ 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 CrO₂ (110) and RuO₂ (110), whose matching alters with CrO₂ magnetization orientation, while TMR in the (001) -oriented MTJs originates from the N\'eel spin currents and different effective TiO₂ barrier thickness for two magnetic sublattices that can be engineered by the alternating deposition of TiO₂ and CrO₂ 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 RuO₂ in functional spintronic devices.