Rhea Hoyer
Altermagnetism constitutes a novel class of collinear magnets exhibiting direction-dependent electron and magnon spectra in reciprocal space with d-, g- or i-wave symmetry [1].
In this talk, I will discuss magnons in altermagnets, particularly how spin splitting emerges, how it can be controlled and give rise to spin transport, and how relativistic effects contribute to the spectrum and transport.
We build a macrospin model for dipolar-coupled magnetic island arrays engineered with altermagnetic symmetries [2]. Dipolar coupling prevents the strict SOC-free limit of altermagnetism, but although SOC splits the magnon dispersion, the magnon spin expectation values show a d-wave-like pattern across the Brillouin zone. This residual altermagnetic character enables direction-dependent spin dynamics and anisotropic spin transport in mesoscopic artificial magnets.
In the g-wave altermagnetic candidate hematite (α-Fe2O3), we show the nonrelativistic spin-split magnon spectra [3]. Spin-orbit coupling (SOC) is important for the magnetic ordering of this material, hence we investigate the SOC-induced dispersion change in the two temperature-dependent magnetic phases of hematite. In both the easy-axis phase below, and the weak ferromagnetic phase above the Morin transition we find that SOC effects are confined to the Brillouin zone center. Crucially, SOC does not mask the altermagnetic splitting at high energies and finite wave vector near the zone edge. This makes hematite an excellent candidate for experimental verification of its altermagnetism, recently confirmed by inelastic neutron scattering [4].
Applying uniaxial strain to hematite reduces its space group from R-3c to C2/c and drives a transition from a g-wave to a d-wave altermagnetic class [5]. This lifts two of the four symmetry‑protected nodal surfaces, reshapes the nonrelativistic magnon dispersion, and enables both spin‑splitter and spin‑Seebeck currents under a thermal gradient, phenomena forbidden in the g‑wave phase.
When looking into relativistic magnon thermal transport in a toy model altermagnet, we find that the time-reversal symmetry breaking allows for a spontaneous crystal thermal Hall effect, as well as a spin Nernst effect, without the application of a magnetic field [6].
These results establish altermagnets as a versatile platform where symmetry, strain, and nanostructuring can be employed to engineer magnon spin transport and thermal‑Hall effects.
[2] R. Hoyer et al., Altermagnetism in magnetic nanoisland arrays, in preparation (2026)
[3] R. Hoyer et al., Altermagnetic splitting of magnons in hematite α-Fe2O3, Phys. Rev. B 112, 064425 (2025) (Editors’ suggestion)
[4] Q. Sun et al., Observation of Chiral Magnon Band Splitting in Altermagnetic Hematite, Phys. Rev. Lett. 135, 186703 (2025)
[5] R. Hoyer et al., Spin Seebeck effect of magnons in strained hematite, in preparation (2026)
[6] R. Hoyer et al., Spontaneous crystal thermal Hall effect in insulating altermagnets, Phys. Rev. B 111, L020412 (2025)