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Altermagnetic (AM) materials have recently attracted significant interest due to their non-relativistic momentum-dependent spin splitting of their electronic band structure which may be useful for antiferromagnetic (AFM) spintronics. So far, however, most research studies have been focused on conducting properties of AM metals and semiconductors, while functional properties of AM insulators have remained largely unexplored. Here, we propose employing AM insulators (AMIs) as efficient spin-filter materials. By analyzing the complex band structure of rutile-type altermagnets MF2 (M = Fe, Co, Ni), we demonstrate that the evanescent states in these AMIs exhibit spin- and momentum-dependent decay rates resulting in momentum-dependent spin polarization of the tunneling current. Using a model of spin-filter tunneling across a spin-dependent potential barrier, we estimate the TMR effect in spin-filter magnetic tunnel junctions (SF-MTJs) that include two magnetically decoupled MF2 (001) barrier layers. We predict a sizable spin-filter TMR ratio of about 150-170% in SF-MTJs based on AMIs CoF2 and NiF2 if the Fermi energy is tuned to be close to the valence band maximum. Our results demonstrate that AMIs provide a viable alternative to conventional spin-filter materials, potentially advancing the development of next-generation AFM spintronic devices.
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Spin-neutral currents for spintronics
Abstract Electric currents carrying a net spin polarization are widely used in spintronics, whereas globally spin-neutral currents are expected to play no role in spin-dependent phenomena. Here we show that, in contrast to this common expectation, spin-independent conductance in compensated antiferromagnets and normal metals can be efficiently exploited in spintronics, provided their magnetic space group symmetry supports a non-spin-degenerate Fermi surface. Due to their momentum-dependent spin polarization, such antiferromagnets can be used as active elements in antiferromagnetic tunnel junctions (AFMTJs) and produce a giant tunneling magnetoresistance (TMR) effect. Using RuO2as a representative compensated antiferromagnet exhibiting spin-independent conductance along the [001] direction but a non-spin-degenerate Fermi surface, we design a RuO2/TiO2/RuO2(001) AFMTJ, where a globally spin-neutral charge current is controlled by the relative orientation of the Néel vectors of the two RuO2electrodes, resulting in the TMR effect as large as ~500%. These results are expanded to normal metals which can be used as a counter electrode in AFMTJs with a single antiferromagnetic layer or other elements in spintronic devices. Our work uncovers an unexplored potential of the materials with no global spin polarization for utilizing them in spintronics.
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- Award ID(s):
- 2044049
- PAR ID:
- 10360673
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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