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PreprintCC BY 4.0arXiv

Exchange-Driven Chiral Magnons and Weyl States in Room-Temperature Metallic XCoB2 (X= Ta, Zr and Hf) Altermagnets

  • Arafat Rahman
  • Tareq Mahmud
  • Alamgir Kabir
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Abstract

Metallic altermagnets remain rare, particularly in low-symmetry three-dimensional crystals where spin-split electronic bands and chiral magnon excitations can coexist. We report a family of metallic dyz-wave altermagnets in the orthorhombic ternary borides XCoB2 (X = Ta, Zr, Hf), which crystallize in the centrosymmetric Pnma structure with G-type collinear magnetic order. Symmetry analysis within the magnetic space group Pnm'a' (BNS No.~62.447) predicts a nonrelativistic spin splitting proportional to kykz, with symmetry-enforced degeneracy on the ky and kz nodal planes, consistent with first-principles calculations. On the kx=0 plane, the momentum-averaged spin splitting reaches 88.4, 52.3, and 70.6~meV at the Fermi level in TaCoB2, ZrCoB2, and HfCoB2, respectively, with maxima exceeding 200~meV in all three compounds. Exchange analysis shows that the altermagnetic magnon splitting originates from symmetry-inequivalent sixth-neighbour inter-sublattice interactions. The chirality splitting reaches 1.51, 2.03, and 3.10 meV below 50 meV in TaCoB2, ZrCoB2, and HfCoB2, respectively, making it accessible to inelastic neutron scattering. Monte Carlo simulations yield N'eel temperatures of 67±1.1, 330±5.7, and 307±5.0~K, placing ZrCoB2 and HfCoB*2 above room temperature. With spin-orbit coupling included, all three compounds host symmetry-protected Weyl points near the Fermi level, Fermi-arc surface states and sizable intrinsic anomalous Hall conductivities σ*zx of +342, −392, and −221~S/cm at the Fermi level, reaching maximum magnitudes of $763$, $942$, and $924$~S/cm for TaCoB2, ZrCoB2, and HfCoB2, respectively. XCoB2 therefore provides a single compensated platform carrying both magnonic and electronic chirality, one in the spin waves and the other in the Berry curvature, without any stray field.

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Cite

BibTeXRIS
BibTeX
@misc{rahman2026exchangedriven,
  title = {{Exchange-Driven Chiral Magnons and Weyl States in Room-Temperature Metallic XCoB$_2$ (X= Ta, Zr and Hf) Altermagnets}},
  author = {Arafat Rahman and Tareq Mahmud and Alamgir Kabir},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.14094},
  eprint = {2609.14094},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.14094},
  note = {CC BY 4.0},
}
RIS
TY  - UNPB
TI  - Exchange-Driven Chiral Magnons and Weyl States in Room-Temperature Metallic XCoB_2 (X= Ta, Zr and Hf) Altermagnets
AU  - Arafat Rahman
AU  - Tareq Mahmud
AU  - Alamgir Kabir
PY  - 2026
DA  - 2026/09/12
PB  - arXiv
DO  - 10.48550/arxiv.2609.14094
UR  - https://arxiv.org/abs/2609.14094
AB  - Metallic altermagnets remain rare, particularly in low-symmetry three-dimensional crystals where spin-split electronic bands and chiral magnon excitations can coexist. We report a family of metallic d_yz-wave altermagnets in the orthorhombic ternary borides XCoB_2 (X = Ta, Zr, Hf), which crystallize in the centrosymmetric Pnma structure with G-type collinear magnetic order. Symmetry analysis within the magnetic space group Pnm'a' (BNS No.~62.447) predicts a nonrelativistic spin splitting proportional to k_yk_z, with symmetry-enforced degeneracy on the k_y and k_z nodal planes, consistent with first-principles calculations. On the k_x=0 plane, the momentum-averaged spin splitting reaches 88.4, 52.3, and 70.6~meV at the Fermi level in TaCoB_2, ZrCoB_2, and HfCoB_2, respectively, with maxima exceeding 200~meV in all three compounds. Exchange analysis shows that the altermagnetic magnon splitting originates from symmetry-inequivalent sixth-neighbour inter-sublattice interactions. The chirality splitting reaches 1.51, 2.03, and 3.10 meV below 50 meV in TaCoB_2, ZrCoB_2, and HfCoB_2, respectively, making it accessible to inelastic neutron scattering. Monte Carlo simulations yield N'eel temperatures of 67±1.1, 330±5.7, and 307±5.0~K, placing ZrCoB_2 and HfCoB*2 above room temperature. With spin-orbit coupling included, all three compounds host symmetry-protected Weyl points near the Fermi level, Fermi-arc surface states and sizable intrinsic anomalous Hall conductivities σ*zx of +342, −392, and −221~S/cm at the Fermi level, reaching maximum magnitudes of $763$, $942$, and $924$~S/cm for TaCoB_2, ZrCoB_2, and HfCoB_2, respectively. XCoB_2 therefore provides a single compensated platform carrying both magnonic and electronic chirality, one in the spin waves and the other in the Berry curvature, without any stray field.
ER  -