Tuning magnon eigenmodes in topological magnets by high-energy electron beams

Magnetic topological materials provide a fertile ground for exploring emergent spin-wave excitations — magnons — and charge–spin coupling, particularly in antiferromagnets (AFM) hosting chiral magnons of interest for low-dissipation spintronics. Here we demonstrate how carrier density and disorder can drive modifications of magnon eigenmodes in the AFM Weyl semimetal MnSb₂Te₄ (MST). By tuning hole density in the p-type MST using hydrogenation [1] we have established a carrier-dependent AFM–FM (ferromagnet) phase diagram: the spin-flop (H₁) and spin-flip (H₂) fields decrease with increasing hole density, and the AFM–FM transition at H₁ is 1^st order. Our charge transport measurements reveal an activated magnon contribution to the longitudinal resistivity, 𝑅_^𝑥𝑥(𝑇)∼𝐴𝑇^1/2exp⁡(−𝐸_𝑚/𝑇), with the AFM magnon gap 𝐸_𝑚 that for H||c collapses at H₁, signaling a chirality switch of magnon eigenmodes [2]. In this work, to disentangle carrier and band-structure effects, we use 2.5 MeV electron beams to dope MST with electrons and introduce controlled disorder in the form of Frenkel (vacancy-interstitial) pairs. Post-irradiation, we find that while Néel temperature remains unchanged, the fields H₁ and H₂ increase and the abrupt chirality switching (𝐸_𝑚⁡→0) appears at a higher field (near H₂), indicating disorder-modified chiral magnon dynamics. We will present the irradiation-dose dependence of  𝐸_𝑚(H) in the Weyl MST and, to elucidate the effects of band-topology on the magnon gap, will compare it with magnon behavior in the e-irradiated topological insulator MnBi₂Te₄ (MBT).

[1] H. Deng, L. Zhao, K. Park, J. Yan, K. Sobczak, A. Lakra, E. Buzi and L. Krusin-Elbaum, Nature Comms. 13, 2308 (2022).

[2] A. Lakra, E. Buzi, J. Moon, A.N. Tamanna, K. Sobczak, K. Park, S. Takei, and L. Krusin-Elbaum, manuscript in preparation (2025).