All-Antiferromagnetic Tunnel Junctions (AFMTJs)

• All-antiferromagnetic tunnel junctions (AFMTJs) are devices composed of antiferromagnetic electrodes separated by an insulator, exhibiting distinct resistance states via Néel vectors or multipolar order parameters.
• They achieve electrical functionality through momentum-dependent spin polarization, symmetry-filtered tunneling, and magnetically uncompensated interfaces despite a vanishing net magnetization.
• Current prototypes implement three operational motifs using spin-filtering barriers, bulk spin-dependent currents, or interface-controlled uncompensated surfaces to enable efficient readout and writing.

All-antiferromagnetic tunnel junctions (AFMTJs) are tunnel junctions in which both electrodes are antiferromagnets and the spacer is an insulator. In these devices, the relevant state variable is the Néel vector in collinear systems, or a higher-order multipolar order parameter in noncollinear systems, while electrical functionality is expressed through tunneling magnetoresistance (TMR), tunnel anisotropic magnetoresistance (TAMR), and current-induced torques acting on staggered magnetic order rather than on a net magnetization (Shao et al., 2023). AFMTJs are therefore the antiferromagnetic analogue of conventional magnetic tunnel junctions, but their operation depends on momentum-dependent spin polarization, Néel spin currents, symmetry-filtered tunneling, and magnetically uncompensated interfaces, all of which permit sizable readout and writing despite the vanishing macroscopic magnetization of the electrodes.

1. Definition, scope, and device archetypes

AFMTJs are commonly written schematically as $\mathrm{AFM}_1/\mathrm{insulator}/\mathrm{AFM}_2$, with two distinct resistance states associated with different relative configurations of the antiferromagnetic order parameters (Shao et al., 2023). In the simplest collinear case, the order parameter is the Néel vector $\mathbf{n}=\mathbf{m}_A-\mathbf{m}_B$; in noncollinear antiferromagnets such as PtMn$_3$, Mn$_3$Sn, Mn$_3$Pt, or Mn$_3$NiN, the operative descriptor is more naturally phrased in terms of chiral spin structure, vector spin polarization in $k$-space, or cluster multipoles such as the cluster magnetic octupole (Kang et al., 3 Sep 2025). This distinction is not semantic: it determines whether transport is most naturally understood through sublattice-resolved currents, momentum-resolved spin textures, or interface-localized uncompensated moments.

A useful taxonomy separates three operational AFM tunneling motifs. Current prototypes exploit antiferromagnets either as spin-filter insulating barriers or as metal electrodes supporting bulk spin-dependent currents. A third, explicitly interface-controlled prototype uses bulk-spin-degenerate A-type antiferromagnetic electrodes whose surfaces are magnetically uncompensated, so that the spin dependence of tunneling is generated at the interfaces rather than in the bulk (Yang et al., 15 Jun 2025). This interface-controlled class is especially important because it shows that bulk spin degener