Abstract
We report the magnetic structure and spin excitations of Mn3Ge, a breathing kagome antiferromagnet with transport anomalies attributed to Weyl nodes. Using polarized neutron diffraction, we show the magnetic order is a k=0 coplanar state belonging to a Γ9 irreducible representation, which can be described as a perfect 120°C antichiral structure with a moment of 2.2(1) μB/Mn, superimposed with weak collinear ferromagnetism. Inelastic neutron scattering shows three collective Q=0 excitations at Δ1=2.9(6) meV, Δ2=14.6(3) meV, and Δ3=17.5(3) meV. A field theory of Q≈0 spin waves in triangular antiferromagnets with a 120°C spin structure was used to classify these modes. The in-plane mode (α) is gapless, Δ1 is the gap to a doublet of out-of-plane spin excitations (βx,βy), and Δ2, Δ3 result from hybridization of optical phonons with magnetic excitations. While a phenomenological spin Hamiltonian including exchange interactions, Dzyaloshinskii-Moriya interactions, and single-ion crystal field terms can describe aspects of the Mn-based magnetism, spin-wave damping [Γ=25(8) meV] and the extended range of magnetic interactions indicate itinerant magnetism consistent with the transport anomalies.
| Original language | English |
|---|---|
| Article number | 054403 |
| Journal | Physical Review B |
| Volume | 102 |
| Issue number | 5 |
| DOIs | |
| State | Published - Aug 1 2020 |
Funding
We greatly appreciate the technical support from T. Dax, R. Erwin, S. Shannon, and M. T. Hassan at the NIST Center for Neutron Research. We thank Shu Zhang for illuminating discussions and patient hearing of ideas. This work was supported as part of the Institute for Quantum Matter, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award No. DE-SC0019331. Y.C. and J.G. contributed equally to this work. J.G. acknowledges support from the NSERC Postdoctoral Fellowship Program. C.B. was supported by the Gordon and Betty Moore Foundation through the EPIQS program GBMF-4532. A portion of this research used resources at the High Flux Isotope Reactor and Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. We also acknowledge the support of the National Institute of Standards and Technology, U.S. Department of Commerce. The identification of any commercial product or trade name does not imply endorsement or recommendation by the National Institute of Standards and Technology. This work is also partially supported by CREST (JPMJCR18T3), Japan Science and Technology Agency (JST), by Grants-in-Aids for Scientific Research on Innovative Areas (15H05882, 15H05883, and 15K21732) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan, by Grants-in-Aid for Scientific Research (19H00650), and by New Energy and Industrial Technology Development Organization.