Tunneling Magnetoresistance in Magnetic Tunnel Junctions with a Single Ferromagnetic Electrode

Magnetic tunnel junctions (MTJs) are key components of magnetic random-access memories. Normally, they consist of two ferromagnetic (FM) electrodes separated by insulating barrier and exhibit a tunneling magnetoresistance (TMR) effect that is a change in MTJ’s resistance when magnetization of the two FM 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 Néel spin current. Using RuO₂ as a representative example of such antiferromagnet and CrO₂ as a FM metal, we perform quantum-transport calculations and predict a giant TMR effect in all-rutile RuO₂/TiO₂/CrO₂ MTJs. The calculated TMR ratio of about 1000% in the (110)-stacked 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)-stacked MTJs originates from the Néel spin currents and different effective TiO₂ barrier thickness for the two magnetic sublattices. Our results demonstrate a possibility of a sizable TMR in MTJs with a single FM electrode and offer a practical test for using AFM RuO₂ in functional spintronic devices.